A honey bee visits a lyreleaf jewelflower (Streptanthus carinatus)
A honey bee visits a lyreleaf jewelflower (Streptanthus carinatus)
Two years ago I witnessed an extraordinary example of a natural embrace between a flower and its specialist pollinator. On the steep slopes of a rain forest of abundant but often hidden flowers, I stood overlooking the Caribbean terminus of the Panama Canal in the Republic of Panama. Bees, wasps, butterflies, and flies flew past me in the forest understory. A pair of blue-crowned motmots called, adding to the din of other birds and wailing cicadas. In the distance, a troop of black howler monkeys bellowed. The local gardens and forest edges overflowed with brilliant orange and red Heliconia blossoms, and flamboyant hummingbirds streaked past my head between their sips of nectar.
My longtime friend and fellow melittologist Dr. David Roubik and I were here as orchid and bee experts to help make the Disneynature feature film Wings of Life. Dave had allowed the producer and film crew to temporarily invade his private rain-forest enclave. Although I’d worked with dozens of independent-film producers, this was my first big Hollywood-style production, complete with line producer, dolly and jib operators, focus-puller, grips, and various assistants. For our shoots, as many as twenty people were on location.
For one scene, we needed a few bucket orchids. They grew in the nearby forest, but it would have been impossible to find in time, so we ordered several plants from a Panama City orchid man. Luckily, he had rare bucket orchids that had large flower buds the day before our shoot. Orchid flowers come in a phantasmagorical array of shapes, colors, and sizes. They epitomize the notion behind my favorite Aussie expression that “flowers like to tart themselves up.” The delicate Coryanthes (C. panamensis) orchids had survived a jolting five-hour drive west from Panama City. Dave and I removed the plants from the Land Rover and lashed their rounded pseudobulbs—with delicate, palmlike leaves—to the base of a buttressed tree. We watered them, then waited overnight like expectant fathers. Would the three precious buds on their slender stalks open into normal flowers? Would male orchid bees from the adjacent forest follow their scent and find the blooms?
At 7:00 a.m. the next morning, Louie Schwartzberg, our Hollywood director, peered over my shoulder smiling. Another expectant father. “Where are the bees?” he asked. “We need to stay on schedule and begin filming.” I mumbled that the flowers were only partially open and not yet releasing any scent. Louis walked away only to return a few minutes later. My heart sank. Were the plants damaged from their long ride? By 9:00 a.m., the wait was over. Before our eyes two gorgeous, fist-size yellow blossoms slowly opened, then filled their bucket basins with slimy drip-tip secretions. Dave Roubik stood beside me with a knowing smile. The flowers were now fully open and they smelled great, spicy but subdued cinnamon with a ripe orange burst tucked inside. Now, we waited.
As if on cue, from the forest edge came a half dozen brilliant green, metallic blue and red orchid bees, male Euglossa. They hovered in midair downwind from our orchids. One after one, they alighted, then scraped at the petals, gathering the orchids’ scent chemicals. Then, doing a methodical, quick shuffle hovering in the air, they transferred the fragrances into the slits on their swollen hind legs. The compounds would attract females later in their lives. One bee slipped on the flower’s rim and fell into the pooled liquid inside the orchid’s bucket. This “accident” had been the orchids’ pollination strategy all along. The bee struggled and moved its legs and tried to crawl through the slippery trough. After several minutes it reached a tiny floral step, a platform serving only for a bee on its way through a narrow passageway to freedom. While holding the bee in a grip at the portal, the orchid glued two pollen packets (pollinia) precisely onto the bee’s back. The little bee peered out, flailing with its front legs. We could not know in advance how long the bee would be held in place by the orchid turnstile. My best, uneducated guess was that this would take only five or ten minutes.
Two hours later, the bee stopped moving. Was it dead from exhaustion? This couldn’t be happening. Louie was clearly troubled. Keith Brust, our director of photography, looked concerned. Maybe Louie could have the CGI (computer-generated imagery) artists work their animation magic so we wouldn’t need an actual bee emerging from the orchid’s stranglehold. Surprising us all (except Dave) the little bee that could gave a mighty push and freed itself from the orchid’s viselike grip. While the cameras rolled, the bee flew off, carrying two golden pollen sacs on its back. Everyone breathed a sigh of relief. Our money shot was in the can, as directors are fond of saying. That day we earned our Hollywood stripes as orchid bee wranglers.
Most orchids are mistresses of deceit. Like the bucket orchid, the majority of the world’s estimated thirty thousand orchid species secrete no nectar and lack accessible pollen grains to entice and feed their bees. Instead, orchid pollen grains are shrink-wrapped inside globose packets—by pairs, fours, and sixes. These pollination bombshells are then glued to their pollen carrier. The sperm-filled pollinia usually get attached to a nutritionally challenged or sex-starved bee. With great precision the flower “knows” what it is doing. It also uses only a specific part of an insect’s body, where its sperm packets cannot be removed by the pollinator. Pollinia are then moved to the right part of the next orchid on a future flower visit by the bee or other pollinator. The pollinator is searching, always searching, and the orchid has evolved so that lights and bells go off in the insect’s brain when it smells or sees an orchid of a particular kind. The evolutionary strategy is not to waste pollen on the wrong type of orchid, but it is also the product of an eerie foray into the mind of an animal by a plant. Like the bucket orchid, many other orchids have evocative and mysterious fragrances. In turn, male orchid bees have scraper hairs along with special storage glands inside their legs to gather up the floral chemical treasures.
A male Euglossa bee spends every day for weeks or months gathering up and storing fragrant chemicals inside pouches almost like a cowboy’s saddlebags on his hind legs. These aromatic treasures come from tropical orchids with tongue-twisting names such as Coryanthes, Gongora, and Stanhopea. Some members of the Philodendron family (Araceae), including Spathiphyllum, also offer bee-enticing odorants. In the absence of flowers, males collect the smelly resins from oozing tree wounds, fungi, a few non-orchid flowers, or even animal excrement. Once the correct mixture of chemicals is acquired within their hind legs, the bees use them to attempt to dominate—as alpha males of many larger animals often do—a site to which females arrive for mating. For the orchid bee, it is a perch site on a tree or woody, upright stem in the forest.
The orchid bees’ mating rituals have been described as bizarre, but are really quite low key and even a bit pedestrian. They wait for hours for their potential mate to appear and occasionally interact with other males, mostly to show who’s who and maintain their territorial positions. Males of each species form a loose group of males that constantly vie to copulate with females. Such “dance ensembles” are known as bee leks, but are hard to find and observe. These orchid bees position themselves a few feet off the ground on tree trunks and then spend many hours performing a stereotyped behavior. A perching male will buzz loudly to fan its wings, visibly lifting slightly off the tree on the tips of its legs. The males apparently release small puffs of their leg chemicals into the air, which they have carefully removed from a hind leg and put on their “wing comb” or the wings themselves, or another part of their body, depending on the kind of orchid bee. The smells and possibly the place, along with the movements or colors of bees, get the attention of both males and females of a single bee species. Most important, it attracts virgin females.
Sometimes male Eulaema bees engage in extensive “jousting matches” in which these insect knights circle head-on at each other, going round and round for many minutes. Perhaps they are sizing up each other, not unlike rival bull elk during the fall rut. After the jousting match plays out, one male, presumably exhausted by having to hold a flight pattern for hundreds to thousands of times, while narrowly avoiding full head banger jousts with its rival, teeters off into the forest. The females do no such acrobatics, nor are they duped to find a male where they were expecting food or a flower (male perches are never near flowers). A female lands on the perch beneath the male, copulation takes place, and almost before the coupled pair hits the ground, the female is back to her foraging and nesting activities, and the male continues as ever. We know the female mates only once, but who knows what these orchid-perfume-besotted bee knights are up to. . . . We look back in time to the 1960s to find out.
Male orchid bees are easily fooled. In 1964, Mrs. Calaway Dodson, the wife of an orchid biologist, was sitting inside her hotel room in Manaus, Brazil—the gateway city to the Amazon—applying her favorite perfume. The perfume contained a trace of cineole, which smells like crushed Eucalyptus leaves. On that fateful morning, the window was wide-open and the humid tropical air ebbed and flowed into the room. A brilliant green male Euglossa, a bee that had followed the alluring scent trail from the nearby forest, entered the room, where it investigated the open perfume bottle. Dodson called to her husband, who came to identify the mysterious intruder. Dr. Dodson determined that the bee was attracted to the flowerlike scent, then watched it collect the fragrance just as if the perfume were a real orchid blooming in the tropical forest. The rest is history. Soon, dozens of orchid floral scents had been extracted and chemically analyzed using gas chromatography and mass spectrometry. Surprisingly, cineole is a common ingredient in many orchids, as well as other flowers.
A pivotal field test of the chemical by another orchid biologist, Robert Dressler of the Smithsonian Tropical Research Institute (STRI), took place at Panama’s Cerro Campana. Putting out cineole and other synthetic orchid baits, Dressler was soon enveloped in a quietly buzzing swarm of two hundred orchid bees, aerialist living jewels. The bees did not harm Dressler, since male bees have no stings. Instead, they were interested in collecting the cineole to enhance their own sex appeal. STRI tropical ecologist David Roubik has set out blotters soaked in various orchid fragrance chemicals in unbroken monthly surveys since 1979, perhaps the longest-ever-insect-population census. The presence of three forest preserves within a day’s drive of his Panama base makes the census possible. Some bees have increased in abundance, but on average he encounters fifty or so hovering orchid bee males at one time, or from three hundred to seven hundred bees in a typical four-hour morning’s census, and fifteen to thirty species in a day. Only male bees are attracted to the chemical baits. Only twice, after surveying nearly a half million bees, says Dave, has he seen females. The females do the usual “bee behavior” foraging for pollen and drinking nectar from blossoming trees and tropical wildflowers, and they do occasionally take a sip of salt from an animal source. The other strictly female bee thing they do is collect nesting material, almost always sticky resins but also mud and some vertebrate feces. It is advantageous for them to be as picky in selecting these materials as in selecting their food and that of their offspring, not to mention their mates. Female orchid bees have ways of assessing “good genes” in their prospective mates, which explains why all this jungle pickiness takes place.
It is not unusual for bee biologists or ecotourism operators to use synthetic chemical baits to attract flamboyant male orchid bees. This is a crowd-pleasing demonstration from Mexico through Brazil. You might be lucky enough to find one of the attracted bees carrying a bright yellow backpack of orchid pollinia from an earlier floral encounter. As different orchids package their pollinia in various shapes and sizes, you can learn to discriminate between a Lycaste and a Catasetum pollinarium based on the number of packets, their shape, size, and whether they have stalks attaching them to the adhesive patch clinging to the bee. Synthetic orchid chemicals are applied to pieces of blotter paper or sponges at chest height on trees from 8:00 a.m. until noon, preferably along a ridgetop. If there is a bit of a breeze, and any bees are nearby, they’ll arrive a few minutes after baiting starts. If you visit or live near a Costa Rican, Panamanian, Ecuadorian, or Amazonian rain forest, give it a try. It’s mesmerizing to be the pied piper for a throng of brilliant metallic euglossine bees. Unlike birds, they have few common names, but some could easily be fashioned. For instance, Hanson’s red-tailed blue bee or Dodson’s fire bee or Dressler’s brassy two-tone. The imperial bee of Panama holds court in the rain forest, and ignites our fascination.
Orchid bees may appear to be flashy celebrities visiting extravagant orchids, but most pollination goes on without notice or fanfare. We met smaller flower-loving beetles in chapter 1 as they munched on white food bodies, the modified petal-like tips of blossoms of the western spicebush (Calycanthus occidentalis). Many blossoms have adaptations catering specifically to members of the order Coleoptera. Rove and sap beetles are attracted to flowers with fruity odors and colors that mimic ripe fruits. Dozens of beetles pile in and begin to feed on loose pollen and the protein-rich food bodies. While eating and defecating, males and females pair up, mating with abandon. Once the food is gone, they clamber out, flying to the next pollen party, unknowingly carrying the pollen on their bodies.
For beetle flowers, the main strategy is to be redundant; that is, to have lots of spare parts. If a few of their succulent petals or stringy stigmas are devoured, plenty are left for pollination and fertilization. Their ovules are ensconced below, out of harm’s way from the clamoring beetles and their chewing mouthparts. Our room-trashing beetles are typically those found visiting Magnolia- and Annona-type blossoms, which are beetle-pollinated-only flowers. It’s a common floral ploy. Botanist Peter Bernhardt reviewed the scientific literature in 2000 and found that thirty-four families of flowering plants contain at least one species pollinated exclusively by beetles, and an additional twenty-two families have species pollinated by a mix of beetles and other insects. Peter also brought to my attention a nineteenth-century cartoon by the French caricaturist J. J. Grandville (1803–47). This entertaining antique image shows a group of partying beetles sitting inside a poppy flower smoking opium.
Why is this relevant? Some of our favorite garden blooms, including the Asian poppy (Papaver orientale), are beetle-pollinated and all came originally from the Middle East. Visit Israel in March and you will find the hairy scarab beetles Amphicoma and Anthypna copulating inside those poppy flowers as well as the blooms of crown anemones (Anemone coronaria), giant orange buttercups (Ranunculus asiaticus), pheasant’s eyes (Adonis), and even one of the wild tulips that gave us some of our showier garden hybrids. What do these flowers have in common? Most make lots of stamens and many tiny ovules, and those beetles really go for orange-crimson petals with black centers. In South Africa, members of the iris family host over eighty kinds of monkey beetles (another group of scarabs), which hold orgies inside gaudy red, orange, or cream-colored, scentless flowers. At first glance, most beetles seem unlikely pollinator candidates. After all, their bodies are hard, smooth, and shiny. Their wing covers—the elytra—are smooth, usually without the hairs needed to hold and transport pollen. Most flower-pollinating scarabs, and other species such as the beautiful jewel beetles (Buprestidae), do, however, sport thick hair tufts on their legs and undersides. This is the architectural result of insect pollen-foraging strategies.
Not all beetles are vandals. A large number, mostly scarabs and jewel beetles, treat their flowers with respect. The flowers also provide a “cruising zone,” a rendezvous site for lusty males that visit flowers in rapid succession, searching for mates. Often, intense, prolonged fights occur among males for access to virgin females. Male and female beetles may remain “en copula” on the same flower for hours as the female placidly eats pollen.
Flies get universally bad press (far worse than beetles). Almost everyone believes that the fly that just executed a perfect six-point landing on his or her plate of Aunt Emma’s prizewinning potato salad is carrying a few billion drug-resistant deadly plague-causing bacteria. Some flies do tote around a few nasty microbes, and others are blood-feeding offenders, including certain female mosquitoes, which transmit life-threatening diseases. However, most flies are benign, even helpful. I’d go as far as saying flies are essential to our well-being and survival.
The order Diptera, the familiar insects we know as flies, is old and diverse. Worldwide, there are an estimated 160,000 species. Of these, roughly 10,000 fly species in at least 71 of 150 dipteran families routinely visit more than 550 kinds of flowers. The predominant flies that frequent flowers are hoverflies and flower flies (syrphids), horseflies (tabanids), and carrion and flesh flies (muscids and calliphorids). There are also highly specialized, long-tongued flies such as the odd-looking humpbacks (Acroceridae) and the long-tongued and elegant tangle-vein flies (Nemestrinidae). Flies are the second most important pollinators of flowering plants, after bees. Even female mosquitoes pollinate blooms. Yes, they are seeking vertebrate blood, but they like nectar and pollinate while visiting the small, green flowers of the northern bog orchids (Platanthera obtusata) for their sugar-rich nectar.
In Arizona and Sonora, I locate flower-visiting flies by triangulating on the high-pitched whine of bee flies (Bombyliidae), whose long-tongued, fuzzy females resemble miniature bumble bees on stilts. In Africa, there are weird horseflies (Tabanidae) with tongues 0.8 to 1.6 inches long. The real champion of exaggerated mouthparts is the tangle-vein fly Moegistorhynchus longirostris, with its 3.3-inch-long tongue compared to its 0.4-inch-long body. It is a floral-nectar specialist, visiting the flowers of at least twenty species in the iris (Iridaceae), geranium (Geraniaceae), and orchid families.
Flower flies (Syrphidae) are my favorites. Syrphids are colorful, diverse, and fascinating flower visitors, insects that are fun to watch. They help ensure that we and other animals do not starve. Flower flies, including the familiar “H-bee,” or drone fly (Eristalis tenax), live in most habitats. Their females visit blooms to sop up pollen grains whose protein allows them to develop their egg clusters. Drone flies are so hooked on eating pollen they are innately attracted to the color yellow. A fly presented with a yellow piece of paper touches it with her proboscis. Many of the world’s more than six thousand flower fly species are brilliantly colored, patterned in brown, black, yellow, and white. Because of their bold stripes, black and yellow aposematism (warning coloration), and their hovering or darting flight maneuvers, they are often mistaken for stinging bees or wasps by their predators and people alike. That cream-colored stalk of bear grass (Xerophyllum tenax) blooming on a mountain in Oregon or Washington may be pollinated by over twenty different hoverfly species.
Still don’t like flies or think we could get by without them? If no wriggling fly maggots lived in rotting plant debris on the ground or in cultivated cacao plantations, the world would be without chocolate bars, delectable bonbons, or cocoa powder! Cacao trees (Theobroma cacao and other species) bear tiny, whitish-pink flowers that emerge directly from their trunks as small clusters. Female midges (Forcipomyia) no bigger than the head of a pin find their way, likely by scent, to the tiny blooms, seeking nectar and pollen food and transporting some grains to other blossoms. Five to eight months later the tiny florets have turned into football-shaped fruits containing the large seeds that are fermented, roasted, and finely milled for the delicious concoctions that chocoholics crave.
Certain blossoms incarcerate their flies overnight. In graduate school, I would drive along Highway 128 south of Lake Berryessa in the Napa Valley and adjacent hills. Here, tall oak trees were festooned with vines. These climbing vines, native to California, are perennial woody vines in the Aristolochiaceae, or Dutchman’s-pipe, family. Their flowers are unusual. Some call them birthworts, as the sacklike flower reminds some people of the shape of a fetus. Aristolochia californica blossoms are almost two inches tall, hollow, and bent in half, looking like miniature, fat tobacco pipes. Thin, parallel, purple lines run from pedicel to the floral opening of these mostly greenish flowers. Three paired, brownish-yellow lips flare open at the entrance to the cavelike floral interior. The blossoms remain open for four or five days before withering. Walking past living curtains of hundreds of draping Aristolochia, I always noticed their distinctive lemony scent, produced inside their flared lips.
On the first day they open, the citrus aroma, and possibly their color, attracts minute flies. Fungus gnats (family Mycetophilidae) alight on the floral lips and walk inside. About a half inch from the base of the flower is a deep purple band. This is nectary tissue, and the temporarily imprisoned flies drink nectar from its glistening droplets, sometimes depositing eggs. Above, the anthers release their powdery yellow pollen. Translucent green tissue around the uppermost region of the flower acts as a window that attracts the flies. On the first day the Aristolochia stigma is receptive and pollen is released. By the second day the glandular hairs forming the nectar ring have dried up, and the pollen-dusted flies exit the now senescing flowers.
Aristolochia californica offers a relatively mild treatment of its fly captives, unlike the forced one- or two-day internment used by various aroids, including almost two hundred species of voodoo lilies (Amorphophallus), the dragon arum from Europe, or the Sumatran A. titanum, the world’s largest flowering stem (it’s a maypole supporting thousands of itty-bitty flowers), with a stalk up to nine feet tall and a powerful stench to match, which attracts carrion-feeding flies. Technically, A. titanum is a collection of many smaller flowers. Its grand architecture is really a huge version of the lowly skunk cabbage and philodendrons mentioned previously. Inside the flowers of A. titanum, also known as the corpse flower, are complex, downward-pointing hairs, which gradually lose their turgidity, allowing the flies to escape. With them the small flies carry their dusting of pollen on the second day of the flowers’ life history. Dutchman’s-pipes such as Aristolochia californica seem to be an early stage in this continuum from always-open and accessible blooms, to the traps of Amorphophallus, which imprison their flies for long periods.
A world away, I encountered the world’s largest flower, which is also fly-pollinated. I traveled with friends, and we had been driving from the coastal city of Kota Kinabalu within Sabah, East Malaysia. We visited tourist locales including Mt. Kinabalu, Poring Hot Spring, the Mesilau Nature Park, and a nearby butterfly farm and insect zoo. But we were after a different rain-forest treasure, the famous Rafflesia arnoldii, one of thirteen to fourteen Rafflesia species unique (endemic) to Indonesia and Malaysia.
Rafflesia arnoldii is a stupendous flower, unlike anything else you will ever see. Surprisingly, the main body of the plant is entirely hidden. It is a parasite of another plant and grows internally. Inside host vines of the genus Tetrastigma in the grape family (Vitaceae), the parasitic monstrose flower and its host live only in undisturbed rain forests. Rafflesia is a flowering plant without leaves, stems, or roots and no green chlorophyll pigments. Almost funguslike it extracts nutrients from its host’s woody vines. Over a period of up to ten months, a bulge forms on the vine and the round, cabbage-size flower buds appear. After this long gestation-like development, the flowers open, but remain viable for only a few days. The immense single flowers are often three feet in diameter and weigh a hefty twenty-four pounds each.
This was the holy grail of floral biology for me. Sure, I’d read about Rafflesia in books and seen photographs. But, experiencing them firsthand in the wild was different; it had been high on my bucket list. We had just passed the small village of Tambunan. Out of my peripheral vision came a fleeting glimpse of something big and red. “Look at that!” I sputtered, bringing our rental car to a skidding stop in the roadside gravel. What, a painted Rafflesia? Sure enough, in front of a small wooden house was a sign crudely painted with the likeness of the crimson giant. Advertising pays. I said, “Selamat pagi,” bidding a hearty good morning to the Malay woman greeting us from the doorway of her home. I negotiated in rudimentary Bahasa Malaysia language for a tour. Were any giant, stinky flowers (Bunga Patma) nearby? Could we perhaps visit and photograph them? My heart was pounding with excitement. I paid the fee of a few Malaysian ringgits, bid her a hearty “Terima kasih,” and our trio of hopeful flower-gawkers was off on our quest. Her agile, ten-year-old son ran us down a forest path leading away from their home.
Behind a low wooden fence lay our prize. I stepped over the low fence and sat next to one of the two wide, maroon flowers. My breaths came rapidly. Rafflesia arnoldii at last! They were two feet across and ten inches thick, leathery tough and otherworldly. They looked like something from the set of a Hollywood 1950s science fiction B movie. Each flower had five broad, flattened arms like a fat starfish. The central disk was surrounded by an incurved thickened bowl. An eight-inch hole led into the darkened interior. Inside were dozens of strange reddish spikes and many anthers, with their slimy, white secretions. Intensely reddish brown, its disk was interrupted by hundreds of irregular creamy patches dotting the entire flower. The smell wasn’t too bad. Yes, it did smell a bit like overripe roadkill, but its deathlike stench was less intense than I’d anticipated. Well, maybe these two flowers were a bit older, not as fresh and appealing as they might have been.
There doesn’t seem to be detectable heat production within Rafflesia blossoms. The long-distance lure for the flies must be their death-and-decay odor plume, and once the insects are close, the blotchy red and white colors and surface texture take over, mimicking the corpse of a large animal. Limited field research has been conducted on the rare, giant flowers, and their separate males and female blossoms which require carrion flies to move pollen from flower to flower. The main pollinators are carrion (bluebottle) flies of the genera Lucilia and Chrysomya. Mostly female flies obtain dorsal loads of viscous liquid pollen perhaps by visiting male Rafflesia flowers. Pollen-laden flies next visit the female blossoms, where they must squeeze inside a groove where the pollen contacts stigmatic areas. No nectar rewards are offered to the flies, only the false promise of a rotting corpse, delectable juices, and a place to lay their eggs.
Let’s examine wasp/flower relationships. Naturalists in the Victorian period were the first to notice that wasps and flies are often found at the same flowers because these two, dissimilar groups of insects appreciate similar odors and color patterns. Sometimes very different animals pollinate and share the same flower. Flowers that appeal to flies and wasps usually lack sweet perfumes and seem dull to our eyes (greenish or brownish, or sort of iodine). Nonetheless, the relatively stinky and icky-colored blossoms offer nectar in large, accessible drops we know are rich in amino acids (the building blocks of proteins). What particular group of insects pollinates most of these “in-between” flowers?
Brown’s peony (Paeonia brownii), in the northwest portion of America (Idaho, Oregon), offers nodding brown cups with yellow rims. Its odor seems almost acrid, and it has big nectar glands that produce lots of dilute sugars and amino acids. When it first blooms, after the snow and ice retreat in April, the most important pollinators are fat, long-tongued flies (Criorhina caudata). You can easily mistake them for small bees, and their hairy coats carry hundreds of peony pollen grains from flower to flower. The flies, though, are fickle. By mid to late April they’d rather visit blooming balsamroots and delphiniums. Is the peony bereft of pollinators? No, the slack is taken up by at least six kinds of wasps that emerge late in spring. They aren’t very hairy and carry far fewer pollen grains than can bees, but they make up for reduced pollinating capacity in their sheer numbers. A single peony flower may be visited by three hungry wasps at the same time.
Based on fossil and DNA evidence, we suspect that one group of small wasps (the pemphredonines) were likely direct ancestors of all hunting wasps and our modern vegetarian bees. We like to think of true wasps as winged hunters of caterpillars, beetles, or flies—carnivores. While wasps are easily observed drinking nectar from various flowers, most don’t mess around with pollen. Under the microscope you find that the hairs on a wasp’s body are straight shafts, while bee hairs are branched, hooked, almost feathery to both gather and hold pollen grains. The branched hairs make up the fine fur coats that many bees wear, which also keep them warm on cold days. Think of bumble bees, which often are out foraging on dreary days.
If few wasps have a mutualistic dance with flowers, then few flowers also attempt to attract and reward these meat eaters. In Europe and North America, figwort (Scrophularia) flowers, cup-shaped, brownish blooms, are visited by social wasps, including native and introduced yellow jackets (Vespula). In my Tucson front yard are beardtongue (Penstemon) blossoms visited by fast-flying bees and masarid wasps. Elsewhere grow passionflowers (Passiflora) or helleborine orchids (e.g., Epipactis), visited frequently and pollinated by wasps. Springtime brings blooms of fritillaries (Fritillaria) to Turkish hillsides. It’s reported that British gardeners are upset when their Fritillaria graeca blooms. The brownish flowers smell like rancid meat, and Vespula wasps come to investigate. It seems that wasps visit brown or green flowers, many of which give off “green-leaf volatiles,” the same chemicals released by plants when being attacked by aphids or caterpillars. Perhaps this is another form of chemical mimicry and floral larceny, which may attract a predator to rid the plant of one of its pests.
The awkward generalization that wasps do not specialize upon flowers has a few exceptions. In North American and African deserts we find a family of flower-loving wasps, the masarids (Masaridae), with long, charming clubbed antennae. Females feed their offspring pollen, not animal fare such as paralyzed spiders, beetles, or caterpillars. The large, slender, brown or black-and-yellow wasps visit native wildflowers including scorpionweed (Phacelia), eagerly gathering up pollen and nectar. Masarids construct nests of pebbles, resin, and mud, then stock their nests with pollen and nectar like most bees. A truly nonconformist wasp.
Everything’s topsy-turvy in Australia. In the woodlands and bush of this drying continent a group of bizarre orchids depend entirely upon the libido of male wasps for pollination. The females are wingless and expect their males to feed them nectar during their mating flights. These flowers sport lip petals that resemble the bodies of female ichneumon and flower wasps. Hundreds of females mimic Australian orchids with iodine-colored flowers. The plants possess evocative common names because the weird flowers resemble tongues (Cryptostylis), spiders (Caladenia), birds (Chiloglottis), and hammers (complete with movable hinge—Drakaea). The male wasps, a bit randy, search the shrubby expanses for receptive females, but pounce on the orchid flowers instead, trying to copulate with them. Botanists and floral biologists call this type of pollination pseudo-copulation. Television audiences are enthralled with nature documentaries featuring the wasps and orchids as the males hang on, not giving up easily with their floral surrogate mate.
Let’s move now from the bizarre and unusual wasps to the sublime but often overpraised butterflies. Certainly butterflies (largely the diurnal Lepidoptera) are icons of beauty. One often watches with pure joy as those sprites flit their way erratically across a blooming meadow. Since antiquity, butterflies have delighted people everywhere. In modern times they appear on every imaginable object as decorative elements and are widely used in advertising and corporate logos. The butterflies have a special meaning to us. The Greek word psyche means “life,” “breath,” or “human soul,” and we find it in modern English words such as psychology. Psyche, as a Roman demigoddess, was represented as a fair young maiden with the wings of a butterfly, not unlike Tinker Bell in the Walt Disney version of J. M. Barrie’s 1904 play Peter Pan. Many cultures find inspiration in the butterfly’s metamorphosis from a lowly crawling caterpillar into the pupal resting stage and finally its glorious emergence and flight into the world as a brightly colored, winged adult butterfly or moth.
Ancient Irish and Mexican/Guatemalan folklore holds that butterflies were souls of the recently deceased. This soul-like depiction was also used in the Oscar-nominated 1983 American and British film El Norte (not to be confused with the 1994 Rob Reiner film of a similar name). Today we can appreciate the winged beauties at hundreds of commercial butterfly houses. In captivity, their chaotic flights are restricted and calmed. They slowly and methodically visit flowers, fruit baits, and sugar-water feeders. We can watch their behavior up close. They even land on our noses and fingers. In Africa, one particular mountain butterfly will land on you if you are wearing something red.
But large butterflies don’t always make the best pollinators; they can be beautiful pollen klutzes. Pollen doesn’t stick easily to their broad, dry, and scaly wings. They are also too leggy, standing up high and rarely contacting anthers or stigmas when they feed from open-topped sunflowers and similar blooms. Even the monarch butterfly and milkweed pollination story is a bit of a stretch. Monarch and queen butterflies (Danaus plexippus and D. gilippus) lay their eggs under milkweed leaves, and their larvae are ravenous. However, adult monarch butterflies, while nectaring at blossoms of native milkweeds (Asclepias), are not dependable pollinators. Their skinny legs rarely slip into the floral grooves, a complex floral mechanism in Asclepias, with just the right orientation. Either their legs don’t get stuck temporarily (remember orchid bees at bucket orchids), or they aren’t strong enough to pull themselves free. Small butterflies are sometimes found hanging dead from the parasols of milkweed umbels, which become death traps. Larger bees and spider wasps (Pompilidae) usually pollinate the milkweeds. Their legs acquire chains of milkweed pollinia.
One group of tropical butterflies, however, are truly pollen specialists. The steamy forests of Costa Rica and Panama are home to a partnership between tropical butterflies and unusual flowering vines in the gourd and pumpkin family (Cucurbitaceae). Here, Psiguria and Gurania vines dangle low to the ground and present strange flowers that attract brightly colored butterflies known as zebra, tiger, or postman longwings (Heliconius). In the same forests, Heliconius also visit the genera Psychotria and Palicourea, of the same plant family as coffee, for nectar and pollen. Together, those butterfly blooms have long, tubular, usually bright orange corollas. In the morning, the butterflies search for flowers that, once located, occupy much of their time, as they drink nectar and acquire large dollops of sticky pollen. Those tropical vines lodge their oily pollen at the bases of the butterfly tongues, making them efficient pollinators.
Photographs of longwing butterflies with their comical big pollen loads always make me smile. They remind me of people with milk mustaches. After acquiring their pollen, longwings often steep their pollen in pools of nectar, allowing amino acids and proteins to leach into the nectar. The resulting nectar smoothie is an ingenious feeding method not used by other butterflies. Added pollen nutrients in their diets allow Heliconius adults to live for as long as nine months, much longer than the average two-week butterfly life span. Of course, not all butterflies visit only flowers. Many visit bird or mammal dung, or even carrion, for liquid nutrients. Especially in the tropics, you may come across dozens of male butterflies “puddling” together at damp roadside mud. Here, they gather essential mineral nutrients—a kind of nectar of mother earth. The minerals are subsequently passed to the females during mating as nuptial gifts.
The less familiar members of Lepidoptera, the moths, fly mostly at night. The diversity of form, color, behavior, and lifestyle of the world’s magnificent moths far exceeds that of their much-beloved diurnal relatives. In the United States, about seven hundred kinds of butterflies can be found, compared to an estimated ten thousand of moths. Most of them lead secretive lives, and many, without fanfare, remain nameless and unknown to science. Only a few moths cause direct mischief and economic loss, such as the few caterpillars that actually eat woolen fabrics in our closets, or those attacking row crops such as corn, and the budworm defoliators of our forest. Yet, perhaps because of their largely secretive, nocturnal habits, the only moth we think we know (or like) is helpless, the long-domesticated silk moth (Bombyx mori) of China. Caterpillars of the silk moth eat only mulberry leaves, and the adults, like those of many moths, eat nothing at all. . . . We need to view moths in an entirely different light to truly appreciate these marvelous insects.
My favorites are the sleek hawk moths or sphingids (Sphingidae). I appreciate them not only for their swept-back wings and fighter-jet look, fast flight, and aerobatic maneuvers, but their intriguing feeding relationships with the blooms they visit. One of the best places to watch “hummingbird moths” are isolated patches of angel’s trumpet or sacred datura (Datura) along mostly dry creek beds in southern Arizona. The blooms of Datura wrightii are delightful. The greenish-yellow buds rise above the leaves, unrolling and expanding at sunset to become nearly twelve-inch-flared and six-inch-wide goblets in less than thirty minutes. Immediately, the lush sweet scent of the blossoms commands your attention. From afar, the moths are noticing it, too, flying in to drink the dilute sweet floral nectar. It has been claimed that the Datura nectar is spiked with nightshadelike poisons, thereby drugging its floral visitors. Common sphinx moth visitors include the omnipresent white-lined sphinx (Hyles lineata) and the somewhat rarer tomato or tobacco hornworms (Manduca sexta or M. quinquemaculata). You may know their hornworm larvae as the ravenous cigar-size, green caterpillars with their thorny tails, defoliating your tomato plants. The larger Manduca hover and drink with extended six-inch proboscides (the correct plural term for the Latin name for “tongue”), but the smaller Hyles dive headfirst into the floral tubes to reach the nectar with their shorter tongues. All depart from the flowers with a light dusting of pollen grains on their tongues and legs—unless they are duped by porch lights, bug zappers, or candles, coming to an untimely early death. Outdoor security lights have spelled the end of night for these insects as much as they have for us.
Growing nearby may be a rare and glorious look-alike blossom, possibly part of a mimicry complex among flowers to lure the same moths. On only a few nights each year, the brilliant white blooms of La reina de la noche (Peniocereus greggii and P. striatus) top the cryptic gray and skinny stems of this rare Sonoran cactus. They bloom during the hottest time of the year when little else dares to flower. Some chemicals in the queen’s fragrance are shared with that of jimsonweed (Datura)—including benzyl alcohol and linalool, part of the odor mimicry suite, and there is a hint of wintergreen, the compound known as methyl salicylate.
Fat Manduca moths visit and pollinate Peniocereus, but their visits are more infrequent than those to Datura. Early the next morning, as the heat and sunlight cause the blossoms to close forever, metallic green sweat bees and honey bees swoop in for the remaining pollen and nectar.
In 1862 naturalist Charles Darwin (1809–82) made a famous prediction about a special duo, a flower and its moth. Growing as newly grown curiosities at Kew Gardens near London and in the greenhouses of Victorian elite plant collectors were magnificent new arrivals from Madagascar, including the star or comet orchids (Angraecum sesquipedale) and other fanciful blooms. Darwin was a serious student of orchids. He was sent a live plant by the great orchid collector James Bateman (1811–97) before 1862. Darwin examined the big, waxy-whitish flower and noted it had a long spur that contained a few drops of nectar within its tip. That nectar tube was nearly a foot long. In a letter to Joseph Hooker (then director of the botanical gardens at Kew), Darwin remarked, “I have just received such a Box full from Mr. Bateman with the astonishing Angraecum sesquipedale with a nectary a foot long—Good Heavens what insect can suck it.” Darwin predicted that there must be an insect, likely a hawk moth, with a great proboscis, long enough to reach far into the depths of the spur to extract nectar, somewhere undiscovered on the island of Madagascar. The problem was that no such long-tongued insect, moth, or other visitor had ever been found in Madagascar, and especially not at star orchid blooms in the wild.
Many people, including his fellow scientists and orchid collectors, believed he was wildly wrong, but Darwin held firm to his prediction. From his other observations of form and fit between bloom and pollinator, research and original observations that became his now classic 1862 book, On the Various Contrivances by Which Orchids are Fertilised by Insects, he believed his ideas about star orchids were correct.
Sure enough, after his death and more than twenty years after Darwin originally made the prediction, a large hawk moth (Xanthopan morganii praedicta) was discovered in Madagascar. Latin scholars and etymologists will note the subspecies praedicta in the moth’s name. Science requiring extensive and costly fieldwork takes a lot of time. Darwin predicted the missing moth pollinator, but field observations and photos of Madagascar hawk moths sucking nectar from this comet orchid, and related species, began to appear only in the 1980s. Research has continued and we now have videos of these elegant big moths feeding at their star orchids.
Across the deserts of the southwestern United States, they stick up like white candelabras, hundreds of massed creamy-white flowers pointed skyward. They are the blossoms of yuccas, or Spanish bayonets, used by landscape architects, and favorites of painters, photographers, and hikers. Fresh blooming stalks are the resting places of a small but essential group of moths. Find a tall yucca stalk in bloom and give it a sharp whack. If you are observant, you may notice a few 0.4-inch-long white moths freed from their floral hideaways. These are the yucca moths (especially the genus Tegeticula), which are obligate specialists on yucca blossoms and will use nothing else. The female moths have bizarre elongate mouthparts called tentacles. Once inside a yucca flower she scoops up masses of the sticky pollen with those tentacles and forms it into a ball. The same tentacles carry the pollen “meatball” to the stigma, then jams it home. This is one of the few cases of active, one could almost say deliberate, pollination in nature. Even bees don’t go to such extremes for their flowers.
Why are only female yucca moths such passionate pollinators? After providing stud service to the Yucca flower the Tegeticula moth turns around and lays her eggs deep inside the ovary. The Yucca plant is trading sex (pollination) for food, some of its own developing seeds. Remarkably, not all the munched seeds are destroyed by the feeding caterpillars. University of Arizona researcher Judie Bronstein and her students discovered that the tiny Yucca embryos are hidden within the thickened rims of the black, triangular seeds and escape destruction. The bright pink caterpillars tunnel and eat their way through the thin centers of the seeds stacked like poker chips. The larvae are doing the seeds a favor by scarifying them so rainwater will penetrate more quickly when they drop to the ground and are ready to sprout.
Recently, we’ve learned that senita cacti are also pollinated deliberately by a different moth, Upiga virescens. This insect, along with yucca moths and some female fig wasps, is the only known example of an active, purposeful flower pollinator aside from us human plant breeders.
We’ve already glimpsed the secret lives of orchid bees and their remarkable host flowers, but we now turn to the lives of their more widespread, less glamorous relatives, who outnumber them by the thousands. Other than the masarid wasps and a few butterflies and flies, bees are the only insects that visit flowers to actively collect pollen as the sole food for themselves and/or their developing brood. Bees also carry nectar back to their nests. It’s kept inside their stomachs, while they carry the pollen grains on their legs or occasionally on their thoraxes. Leafcutters and related bees (Megachilidae) may also have Velcro-like aprons on the underside of their abdomen, while some of our spring mining-bees (Andrenidae) have pollen-carrying hairs on their hind legs. With the exception of a few tropical bees that ingest protein from carrion and dung, almost all of the thousands of bee species are strictly vegans.
Bees are world-champion pollinators because of their ancient specialization upon flowers (70–100 million years ago, according to the earliest fossils), and their ability to learn and manipulate complex floral signals, shapes, colors, and odors. Moreover, they can fly, sometimes for miles, to their foraging sites. They also have finely branched hairs coating much of their bodies. The interstices catch and hold the pollen grains. With other hairs and leg parts modified into combs and scrapers, they quickly and efficiently groom themselves, packing the nutritious pollen onto their fluffy hind legs or undersides. Bees recover most but, fortunately for the plant, not all the pollen on their bodies. Many plants deposit pollen where the bees can’t reach it or forget to look for it. Less than 1 percent of the grains become lodged between leg bases, under tongues, or on a narrow stripe down the bees’ backs. The refugee pollen resides in those safe sites and is carried from flower to flower. This is essential for flowering-plant reproduction. For millions of years plants have been hiding their pollen on bees in places where they can’t groom it off, where it remains until accidentally brushed onto the receptive stigmas of flowers.
Most of the world’s twenty thousand described bee species, like ants and their wasp ancestors, are ground nesters. Bees are often mistaken for wasps. The habitats where bees prefer to live, and where we find their highest diversity, are the sandy, well-drained soils of deserts and savannas of the world. Tropical soils are too wet most of the year, so the social bees living there nest inside trees, sealing their nests with fast-drying and water-repellent resins. In any given habitat about 10–20 percent of the bee species are specialist cavity nesters in broken, pithy stems (such as elderberry or dried blackberry canes), small cervices, or vacant beetle galleries in wood. If you have a wooden deck at home, you may know that carpenter bees (Xylocopa) use their powerful jaws to excavate galleries in wood. Most wood-nesting bees, however, aren’t able to dig their own tunnels. Ironically, they depend on the life cycles of flower-visiting beetles, especially long-horned (Cerambycidae) and jewel beetles (Buprestidae). The beetle grubs burrow and eat their way through tree trunks and branches. When the grub changes into a winged adult, it chews an escape hole, leaving its former nursery to female leafcutter and mason bees, which move in and begin nesting.
Most bees are floral generalists that visit many different species of flowers for pollen and/or nectar. In deserts, these specialist bees predominate. They include cactus-loving bees, mallow bees, and sunflower specialists. Some confine their shopping to one closely related group (a genus) of wildflower or shrub species.
A common misconception about bees is that they are all social, live in populous colonies, and make honey—the whole Winnie-the-Pooh scenario. In fact, there are only eleven species of true honey bees (Apis) and but one widespread honey-making bee (Apis mellifera), which evolved in the Oriental region (it later spread on its own to Africa and Eurasia and later everywhere else, thanks to us). The tropics have over five hundred species of stingless bees (meliponines), and they hoard enough honey to make honey harvesting (beekeeping) by humans worthwhile. About forty-seven species of bumble bees (Bombus) live in the United States, with some two hundred fifty species worldwide. They are also social honey-makers but store only a few teaspoons of honey, so digging up their nests isn’t worth their defensive (and painful) stings. They are perhaps loved by their enemies for their brood, while their flower-visiting behavior is what makes them ever so important to plants, other animals, and people.
Some flowers protect their pollen from pollen robbers and other insects that make poor pollinators. Almost 8 percent of the world’s 250,000–300,000 known flowering plant species play this hide-and-seek pollen game with bees. Pluck a tomato flower from your vegetable garden and examine it with a loupe. The central part of the flower is a bright yellow “cone” of five anthers encircling the female pistil. Each anther tip has holes, the apical pores. This is the only way the small, light, and dry pollen grains can escape. Imagine the flower is a botanical saltshaker. Tomato flowers offer only pollen. No glands ooze sweet nectar. Tomatoes aren’t the only crop plants to make saltshaker flowers. Blueberries, cranberries, chilies, eggplants, and kiwis have them as well, but blueberry, cranberry, and chili flowers also secrete nectar.
Female bumble bees, and a few other bees, seek out flowers that have perforated anther tips. One of my favorite activities is to sit quietly near a nightshade (Solanum) or partridge pea (Senna) patch in the Sonoran Desert. Before sunrise female bees begin arriving to forage for pollen inside these nectarless flowers. A bee lands on a flower near me. She bites into the anther cone with her jaws (mandibles) and curls into a C shape with her thorax covering the anther pores. I hear a funny sound, like someone giving me the raspberry, but it’s coming from the bee. The bee is emptying the anthers with her sonic vibrations! The comical sounds I hear are an ancient pollen-harvesting technique used by bees around the world on this kind of blossom, called buzz pollination. The bees are living tuning forks. Using the powerful flight muscles inside their midsections, the muscles that power the wings in flight, they contract them with wings held flat and unmoving over their backs. The sound and vibrational frequencies are about three hundred to five hundred cycles per second (Hz). If you’re a musician, you know these sounds to be in the range of the musical notes A or middle C.
Buzz flowers cater to a specialized group of bees in the know. Ordinary bees and other insects cannot extract the pollen grains from these blossoms. The bees’ sonic buzzes get the pollen grains bouncing into each other inside the anthers. The pollen grains reach their escape velocity and stream forcefully out of the anthers by the hundreds of thousands in a few tenths of a second. Measurements of buzzing bees reveal they impart 30 g (1 g is equal to acceleration due to gravity at the earth’s suface) to the pollen inside the anthers. By comparison, fighter pilots can withstand about 9 g-force with training and by wearing a special pressurized anti-g-LOC suit. An untrained person typically blacks out and loses consciousness, due to blood loss from the brain, at only 5 g.
You can put buzz pollination to use in your daily life. If you grow tomatoes in a home garden and you don’t have bumble bees around, try this. Get the appropriate A or C tuning fork, an electric toothbrush, or a new commercial product called the VegiBee. This novel device is essentially a modified electric toothbrush with some clever marketing. Now, you are the sonicating bee as you move from tomato flower to flower. Your reward will be tasty, homegrown tomatoes a few weeks later. It’s quite an accomplishment. You can do what commercial honey bees can’t. They aren’t equipped to buzz pollinate or don’t learn the behavior needed to sonically harvest pollen from porose anthers.
Wild pollinators, including leafcutter, mason, stingless, digger, sweat, and bumble bees, along with the wasps, beetles, flies, butterflies, and others we’ve heard about, all contribute to modern agriculture, literally every third mouthful of food we eat or drink. In the United States, annually about $3 billion of agricultural productivity is made possible by the foraging and pollinating activities of unmanaged wild insects visiting flowers of more than 125 American crops and about 1,400 worldwide. Managed honey bee colonies contribute the remainder of the approximately $10–$15 billion annual US total agricultural production. In the tropics, the stingless bees are the rising stars in pollination. Their colonies are smaller, forage freely but in a smaller range, are less heavy and also easier to manage, and are now being propagated and moved to different crops.
To balance our pollinator portfolio and not become entirely, and dangerously, reliant upon the ecosystem services of one introduced insect, the European honey bee, researchers have domesticated and developed new agricultural pollinators from a bevy of natives and one introduced bee. In the 1930s farmers in Utah noticed that they had some new livestock in their buildings, literally living inside the wooden beams and roofs of their barns. Eurasian immigrant bees had arrived and were spreading fast. The new bees were alfalfa leafcutter bees (Megachile rotundata), and they took up residence in nail holes and crevices in weathered lumber.
Alfalfa farmers were quick to notice that these small, black, housefly-size bees were supremely efficient pollinators of their major crop, alfalfa. They started drilling and hammering holes in their barns like mad. Given a choice, honey bees don’t preferentially visit alfalfa blossoms, but the diminutive leafcutter bees pushed alfalfa yields from 198 pounds of cleaned alfalfa seed per acre to an astounding 2,000 pounds per acre. Today, alfalfa-seed farmers buy five-gallon buckets, each containing about ten thousand leafcutter bee cells, for about $100 from bee brokers or bee ranchers in Canada. They deploy them on mobile trailer shelters among the blooming expanses of their alfalfa fields. The leafcutter bees live inside paper straws or prefabricated Styrofoam boards. These alien bees make possible the nearly $5 billion annual value of the US alfalfa crop. You may not realize the importance of alfalfa seed grown into alfalfa plants and used for hay as livestock fodder. These and other bees help put meat on our tables as well as adding delicious fruits and many edible seeds to our diets.
A native bee of the Pacific Northwest is the blue orchard bee (Osmia lignaria), or more colorfully, BOB. These industrious bees visit and pollinate the blossoms of many tree fruits in the rose family. The bees are especially fond of sweet cherry blossoms for their pollen and nectar. A few dozen female BOBs living in cardboard straws and small shelter boxes within an orchard can do the work of an entire honey bee hive containing up to thirty thousand bees.
Bumble bees are the pollinator of choice for pollinating greenhouse tomatoes and green peppers around the world. My favorite farming operation to visit is a three-hour drive from my home. Here, north of Willcox, Arizona, four hundred acres are under glass, an immense tomato factory. EuroFresh Farms, a formerly Dutch-owned and operated facility, hydroponically produces one of every six tomatoes on the vine clusters sold in US markets. Workers ride electric carts on rails to harvest the tomatoes, then electric tomato trains bring the ripe fruit to the sorting and packing house. None of this could happen without bumble bees (Bombus impatiens) to buzz pollinate and set the crop. Bumble bees are raised by insectary companies in other states, then flown and driven to EuroFresh Farms. The bees are licensed for their pollinating services per cubic yard, and the spent colonies are traded out every few weeks for fresh younger colonies.
European honey bees are the de rigueur pollinator for the majority of today’s agricultural crops. They can be raised and the colonies divided at will to produce more bee colonies. Since the 1860s and the Civil War era, beehives (known as Langstroth hives) have been used by beekeepers. Their interchangeable-frame technology enables apiculturists to easily extract honey, along with managing and inspecting their bees. The commercial migration of a million or so of our just over 2 million managed honey bee colonies follows the American bloom, mirroring the seasonal progression of crops and wildflower blooms across the nation. Most commercial beekeepers don’t earn their living from the backbreaking labor needed to produce honey. Instead, they lease their Lilliputian livestock to agricultural growers. Today, the primary imperative in commercial beekeeping is to get your eighteen-wheel semitrailer truckloads (carrying about four hundred hives each) to Southern California in February, just ahead of the ephemeral almond bloom. Beekeepers no longer reward growers with a five-gallon bucket of tasty honey for allowing them to place their bees on nectar-rich croplands.
Pollination contracts are signed a year in advance, and the money is good. For the California almond-bloom gold rush, beekeepers rent their hives to almond growers for $150 or as much as $200 each. Each year there is an increasing shortage of available honey bee colonies, caused by colony collapse disorder (CCD), neonicotinoid insecticides (neonics), mites, diseases, and other factors. The hives rest four to a pallet and are placed one or two per acre, for just two or three weeks during the hasty almond bloom. With about seven hundred thousand acres of prime California agricultural land planted in almond orchards, this is indeed big business in bees. Honey bees pollinate most of the world’s agricultural crops. Honey bees, however, are too often credited with pollinating buzz-pollinated crops, including blueberries and cranberries, which are largely pollinated by wild bumble bees, unbeknownst to the growers, who pay for leased honey bee pollination services.
If you live in North America, you may have witnessed the incredible flights and flower visits of those tiny marvels the hummingbirds (Trochilidae). Weighing only 0.07 to 0.70 ounces (a penny weighs just 0.08 ounce) and beating their wings at up to two hundred times per second, they are the only birds able to hover, fly backward, or upside down. With their diminutive size and outlandish metabolism, they constantly need energy, the sugar rush they get from floral nectar. To be able to sleep and not perish at night from starvation, they tune down their metabolism and become torpid, their heartbeat and breathing slowing down. Each morning, breaking their nighttime torpor, they go in search of new flowers to power their flight and sustain their lives.
In Sonoran Desert washes we find spectacular red-bloomed plants visited by hungry migratory and resident hummingbirds. Chuparosa bushes (Justicia californica) are visited by numerous chupamiel (“honey sippers,” poetically in Spanish). On adjacent hillsides, hundreds of coach-whip-stemmed ocotillos (Fouquieria splendens) point skyward. Beginning in March, for a month, their branch tips burst forth in riotous torchlike, red blooms. The plants are eagerly patrolled and defended by territorial male Anna’s, black-chinned, and rufous hummingbirds, while the females try to sneak in for an unmolested drink.
These bird blossoms share several common features. First, they are brightly colored, in the case of chuparosa and ocotillo, brilliant red. Flowers visited by hummingbirds can also be yellow, orange, or other colors. Their nearly odorless flowers are thin and tubular, perfectly adapted to the fit of the narrow, long beak of a hovering hummingbird, but provide no place for a bee to land. The flowers are reinforced with strong veins to resist the “poking” bills. The scant pollen is usually deposited in small patches on the crown of the bird’s head or at the base of its bill. The flowers that hummingbirds visit are attuned to their visitors’ energy needs. These flowers produce abundant but weak nectar, usually 17–25 percent total dissolved sugars. Hummingbirds need to drink often. When these feisty, little birds aren’t sipping nectar, they are chasing down tasty fruit flies and other small insects around flowers, providing essential proteins and fats in their diets. In North America, at least 130 flowering plants are dependent upon various kinds of birds for their reproduction.
You can predict in a science-based way what kind of pollinator might drop in to visit any flower just by looking at it and paying attention. Taking note of a flower’s color, shape, food rewards, and type of scent will go a long way toward predicting what animal (or wind or water) might pollinate a wildflower, or a flower in your garden. In the past this has been called the pollination syndrome approach. Applied to our ocotillo blossom above, it reveals a high likelihood that a tubular red, orange, or yellow blossom with abundant but dilute nectar and no scent will attract hummingbird visits but hardly any from bees, butterflies, or bats. The pollination syndrome concept has, however, been controversial among academic floral ecologists. I find it to be a wonderful and evocative entrée into “thinking like a pollinator” and understanding flowers.
Around the world, we find many other bird-pollinated flowers. True, hummingbirds are confined to our western hemisphere, but if you take a holiday to Hawaii, you might glimpse vibrant-colored birds with long, curved beaks, bills that fit certain blooms. These birds and blooms are found nowhere else. Hawaiian honeycreepers (Drepanididae, related to canaries) were once abundant in all Hawaiian forests, with 51 species. Today, due to forest destruction, predation from feral imported animals, and avian malaria, a dozen species are already extinct, with another fourteen imperiled.
Of these birds, perhaps emblematic of the group is the scarlet-colored ‘I‘iwi (Vestiaria coccinea), the third most commonly observed honeycreeper. The ‘I‘iwi has a sharply down-curved bill like most of the honeycreepers, an adaptation for probing into its preferred blossoms in search of nectar. The flowers are modified so that when the birds drink, a tiny amount of pollen is dusted onto their foreheads and transferred to the next flowers as they feed. The ‘I‘iwi is a spectacular sight when perched or feeding on the brilliant blue flowers of opelu (Lobelia grayana) at the Waikamoi Preserve on the island of Maui. Among the floral hosts of the honeycreepers are 125 species of lobelioids in six genera, e.g., Clermontia, Cyanea, Lobelia, and Trematolobelia. Several species of those genera are extinct on certain islands and endangered on others. All have curved floral tubes that closely fit the beak curvature of the various honeycreepers. If you visit Waimea Canyon on the island of Kauai, you can watch at least three different honeycreepers (including the ‘I‘iwi) gorging on nectar in the bright scarlet bowls that bloom on the Kauai bottlebrush tree (Metrosideros waialealae). It’s a cousin of eucalyptus and myrtle.
Traveling down under, you find other beautiful birds with a sweet beak for nectar. During a stay with my family in bushlands near Canberra, Australia, I fondly remember hearing and seeing a noisy friarbird (Philemon corniculatus) feeding on nectar from the stout, curved, red, orange, or purple blossoms of Grevillea species. Here, we find abundant honeyeaters, sunbirds, Australian chats, and various colorful lorikeets, the latter a group of true parrots. You may have visited a zoo, such as the St. Louis Zoo, and had the pleasure of watching and feeding surreal rainbow lorikeets, enjoying them lap up sugar water from a cup with their brushy tongues.
In all, about 170 honeyeater species (Meliphagidae) are found throughout the Old World section of the Pacific basin. The family is extinct in Hawaii, but 70 species live in Australia proper. The dominant pollinating passerines (perching birds) in Australia belong to the honeyeaters, sunbirds (Nectariniidae, one tropical species but charming), thornbills (Acanthizidae), and silvereyes (Zosteropidae). None deliberately eat pollen. Pollen eating is restricted to true lorikeets (7 species in Australia and about 55 species through the Pacific basin).
The sunbirds are small songbirds, including about 132 species, more common in Africa and tropical Asia than in Australia. In the Republic of South Africa, you might be rewarded with visits of brilliant yellow, purple, and green, metallic-plumed sunbirds such as the variable sunbird (Cinnyris venustus) feeding from flowers of cape honeysuckle, or from aloes in Tanzania. Arborescent forms of aloes, the tree aloes, are favorites of sunbirds across much of southern Africa. Other nectar-feeding birds from tropical islands in the Indian Ocean, the western Pacific, subtropical Africa, and back in Australia are the charming little passerines the white-eyes (Zosteropidae). Although insectivorous, they can be found feeding on flowers for nectar. One, the mountain black-eye (Chlorocharis emiliae) is frequently encountered feeding at Rhododendron blossoms on the slopes of Mt. Kinabalu, Sabah, Malaysia.
In almost all flowers pollinated by birds the stickiest pollen is deposited on the base of the bill (as in many hummingbirds), while the “drier,” less greasy pollen (usually in the form of lobed or spiny pollen grains) is deposited between the feather barbules on the bird’s forehead or breast. The main exception is the African bird-of-paradise plant (Strelitzia reginae), routinely planted as an ornamental in Orange County, California. In their native African homelands birds alight on the massive orange and blue blooms to sip nectar. The perch isn’t a good one. Rather, it evolved to make the birds’ feet slip. As the birds try to retain their grip, the sticky, white pollen clumps end up between the birds’ toes. Well, it doesn’t happen this way in the California gardens because the local nonadapted birds don’t know how to work the flowers. Most of the pollen stays put, and these garden ornamentals rarely produce fruits.
Something strange is happening at hummingbird feeders across southeastern Arizona. A few decades ago, bird-watchers living in Portal, Arizona, dutifully filled their hummingbird feeders with fresh sugar water every evening, to be ready for the early-bird hummingbird onslaught the next morning. By morning, however, their feeders were always drained dry. What was going on? The same thing has been happening in Tucson since about 2006. Who were the thirsty and mysterious nocturnal marauders?
They’re bats! These intelligent animals had learned a new foraging trick and seem to be able to communicate the location of feeders to other bats in their roosts. Why spend a lot of energy flying many miles looking for cactus blooms when you can rob from sugar-water feeders conveniently supplied by birders? Each summer the bats dependably return to raid the bird feeders from about mid-August until early October. Two species of nectar bats, the southern long-nosed bat and the Mexican long-tongued bat (Leptonycteris yerbabuenae and Choeronycteris mexicana) are migrants to southern Arizona from regions farther south in Sonora, Mexico. Along US and Mexican flowering-nectar corridors the nectar bats roost by day in caves and mines, then by night forage dozens of miles to feed upon the sweet nectar of agaves (also called century plants) and columnar cacti.
A Mexican long-tongued bat (Choeronycteris Mexicana) drinking nectar from flowers of a century plant (Agave p. palmeri)
Charismatic nectar bats have pointed faces like sleek greyhound dogs—unlike most bats. They also have long—up to half their body length—brush-tipped tongues. Watching them feed at the broad panicles of agaves, or the goblet-shaped, white flowers of saguaro, is awe-inspiring. What happens in the blink of an eye has been slowed down with high-speed cinematography in recent television documentaries. In less than one second, the bat hovers at the blossom and thrusts its entire head and neck into the bloom. Backing out of the flower, its fur is coated with pollen, later groomed off and eaten. Interestingly, these bats do not forage alone but in groups of dozens. Wave after wave come to the melon-scented saguaro or coconut-like Palmer’s agave (Agave palmeri) across the Sonoran and Chihuahuan Deserts of Arizona, New Mexico, and northern Sonora, Mexico. Both kinds of flowers offer copious amounts of nectar and lots of tasty pollen. Each saguaro flower may have as many as four thousand anthers and up to a teaspoon of nectar.
Just because you’re not a bat and can’t fly doesn’t preclude flower-visiting in your feeding repertoire. A small but diverse group of wingless but adept climbing mammals routinely visit flowers for nectar and pollen. Perhaps the most amazing nonflying mammal to visit flowers is the honey possum (Tarsipes rostratus). An Australian, toothless marsupial, it is only 3–4 inches long and weighs about half as much as a house mouse. These animals have a long snout and tongue to reach into their favorite blossoms. The tongue is tipped with brushlike cells. Mostly nocturnal, they climb into the leathery foliage to reach the nectar contained inside the intricate, tall blooms of Banksia, Adenanthos, and Calothamnus. The honey-possum homelands are restricted to the heaths and shrublands of Western Australia.
In the Karoo region of South Africa, rodent pollinators, including two gerbils, visit the African lily (Massonia depressa). Rodent pollination in the southern hemisphere was first recorded on Protea shrubs (relatives of the Aussie Banksia). Also in South Africa, long-nosed cape rock shrews (Elephantulus edwardii), also known as elephant shrews because of their long noses, lick the nectar of the African pagoda lily (Whiteheadia bifolia) and pollinate its nondescript, small, green flowers. Within the southern hemisphere, there could be as many as fifty-nine species of nonflying mammals, rodents, that visit almost a hundred different plants for their sticky snacks.
Well, not begonias, exactly, but a few flowers are visited by reptiles, lizards in fact. It happens most often on islands where pollinators are few and colonizing plants evolved in association with hardy animals that had the opportunistic eating habits required for survival under harsh, insular conditions. While the dinosaurs of the Cretaceous period may have watched early bees buzz by 100 million years ago, scientists now have examples of living flowers pollinated by lizards, of all things. The remote island of Mauritius in the Indian Ocean is a distant twelve hundred miles from the southeastern coast of Africa. Once the home of the flightless dodo bird, Mauritius has plenty of other botanical and zoological oddities.
Many strange flowering plants live there and nowhere else. Several Mauritian plants have highly unusual nectars. One is truly bizarre. A kind of bellflower without a better common name, Nesocodon mauritianus has bloodred nectar. Two other endemic Mauritian species have red and yellow nectars. Even a nonchalant weekend gardener would recognize sanguineous nectar as peculiar. All floral nectars are colorless, right? What possible function could colored, or fluorescent, nectars have? Several Swiss researchers think they have the answer. Found nowhere else, cliff-loving day geckos (Phelsuma ornata) on Mauritius are regular visitors to the bellflowers and mallows, and their blooms. The colorful red and yellow nectars in these accessible flowers seem to function as honest signals to the geckos. The climb is worth the effort since sweet nectar is present. Additionally, the nectar may contain bitter chemicals meant to keep away omnipresent nectar-robbing ants, while remaining tasty fare for the lizards. Around the world, as many as sixty plants species, belonging to fourteen families, may have colored nectars.
Living on the Poor Knights islands near New Zealand are other lizard pollinators. Duvaucel’s gecko (Hoplodactylus duvaucelii), New Zealand’s largest native gecko, is a regular flower visitor. It feeds on Poor Knights flowers including ngaio (Myoporum laetum), the Poor Knights lily (Xeronema callistemon), with its large, red bottlebrush floral clusters, and the glorious red-flowered myrtle pohutukawa (Metrosideros excelsa). These twelve-inch-long geckos climb the plants in search of their abundant sweet nectar. Curiously, Duvaucel’s gecko has evolved modified throat scales in response to its new flower-loving (anthophilous) behaviors. These are believed to be an adaptation to better catch, hold, and disperse pollen grains, in much the same way that bees evolved branched hairs, differentiating from the unbranched, simple hairs of their wasp ancestors.
Most of the lizard pollinators are geckos and are expert climbers, just like those little, nonflying mammals the pollinating honey possums and elephant shrews. Climbing skills, not wings, give these animals access to a new banquet of flower foods. It is not too surprising to learn that a few lizards raid flowers for nectar and may become semidependable pollinators. On some islands of the Seychelles, in the Indian Ocean, certain geckos (Phelsuma) visit rare palms including the “coco de mer” (Lodoicea maldivica), which produces the largest nut on the planet (its shell can be carved into a drinking bowl), and the mature fruit looks surprisingly like the lower half of a nubile woman (perhaps at least in the mind of a lonely sailor). It’s hard to believe that each huge fruit (weighing in at sixty-six pounds) is produced by a thirsty lizard, and/or the wind, playing Cupid.
It isn’t just lizards, beetles, bees, and the tropical breezes that pollinate palm trees. People pollinate palms, too, and they have been doing so for millennia. Humans, or at least winged deities, as pollinators are figured in a twenty-five-hundred-year-old bas-relief carved into an Assyrian temple wall and now owned by the British Museum in London. The technique for pollinating date palms is something of an anachronism. Yes, it has been mechanized, but orchardists haven’t changed the technique, invented three to seven thousand years ago. Today, just as their fathers and grandfathers did before them, in villages across Iraq, Iran, Syria, and Egypt, adolescent boys climb date palms (Phoenix dactylifera). Kids pollinating date palms anywhere is no fun. Date-palm fronds and trunks have curved and brittle spines that easily break off into unprotected flesh. With a curved, short metal knife the boys cut away the tough outer sheath (spathe) protecting the delicate receptive female flowers within. They cut off the tips of the flowering stems and carefully insert branches of pollen-laden male flowers they brought with them. Those laborious actions are repeated for each branch on the female trees and for every tree in the tall date-palm orchards. Pollen from the male blossoms fertilizes the female flowers. The delectable sugary dates follow months later.
Although not climbed by armies of barefoot young boys, the many acres of Medjool Date Palms, familiar to Southern California drivers zooming through the Mojave Desert cities of Indio and Twentynine Palms, are still pollinated by hand by farmworkers climbing on skinny wooden ladders into the feathery crowns of the tall palms.
It’s a logical progression. People can and have learned to become pollinators, too. By necessity, we have learned to pollinate flowers to produce foods and bring their special beauty into our lives. Humans learned to pollinate flowers in antiquity, in the case of date palms and likely other agricultural crops, to increase yields. Sometimes in the past, entire cultures have forgotten how to do it, forgotten the secrets of hand-pollinating flowers, assuring yields and seeds for future plantings. For modern, especially Western, cultures, people fulfilled pollinator roles following the realization of flowering-plant sexuality by England’s Nehemiah Grew (1641–1712), the binomial and plant sexual classification system of Linnaeus (1707–78), and the marvelous book and copper-plate flower engravings of Germany’s Christian Konrad Sprengel (1750–1816). A big jump in the use, spread, and appreciation of garden hybrid roses and numerous lilies followed soon after. Irishman Arthur Dobbs investigated the garden tulip and hand-pollinated them around 1750. This amazing man was also a North Carolina landowner and former governor, a neighbor of Jonathan Swift’s, the discoverer of the Venus flytrap (Dionaea muscipula), and ardently dedicated to the search for a Northwest Passage through the Canadian Arctic.
We can think of the last two hundred years as a frenzied time of people hybridizing different things, or creating new varieties of garden and cut flowers. Surprisingly then, even with the popularity of gardening, few modern American gardeners know how to make the simplest crosses, or even how to pollinate squash or zucchini blossoms in need of pollen when the right bees (Peponapis or Xenoglossa) aren’t around.
Later in this book, we will learn the origins and extent of plant breeding. The corporate and academic plant breeders and agronomists today make carefully controlled crosses between parental plants. They bag flowers to isolate female blossoms and to collect and store their pollen. Sometimes they shoot DNA-laden gold particles into the nuclei of leaves or tissue-culture plantlets to bypass the sexual process, creating new strains or hybrids. Today, in places in China women climb high into apple trees, brushes and pollen in hand, and provide a workforce of human bees. Their lands are now poisoned with insecticides and too few honey bees or wild bees are left to pollinate the flowers that can become fruit. That is one explanation of this peculiar plight. Another, perhaps equally likely, is that nobody considered the self-infertility of apple clones. A given clone is compatible only with certain other varieties and cannot produce a single seed or fruit from its own pollen.
Closer to home, I’m willing to bet that gardeners might learn new tricks and try their hand at being bees and other pollinators. Indigenous North American farmers and some recent Hispanic immigrants living in the southwestern United States have not completely abandoned or forgotten their ancestral gardening ways. Get out your VegiBee or old-fashioned artist’s brush for cucurbits and other vegetables. Try creating your own blue rose or fancy tulip, something that hasn’t arisen in nature.
Out of necessity, curiosity, and our innate drive to create and manage beauty, with almost godlike manipulative powers in the case of modern plant breeding, we are pollinators. Begun in the Fertile Crescent countries seven millennia ago with date palms, and longer for the cereal crops, our “matchmaker” talents with the flowers of agricultural plants continue into modern times, kept alive by seed-saving farmers. Throughout the history of Homo sapiens we have been and are on-again, off-again pollinators, intermittent go-betweens in the world of flowering plants. Curiously, we do something that flower-visiting insects, birds, bats, and others won’t do, or can’t do. We collect, multiply, and hoard the plants we love for the unique beauty of their flowers, to ornament the land around our homes, our interior living and work spaces, and, of course, each other.
