A butterfly’s wing is covered with tiny overlapping scales. These gave rise to the name Lepidoptera, from the Greek for “scaly wing.”
Butterflies may well be the best loved of all insects. For millennia, they have attracted the attention and admiration of people around the world. This is not surprising as they are large and showy for insects, and they do not bite or sting. Their metamorphosis from caterpillar to winged adult has captured the imagination of many writers and artists, and this process has come to symbolize beauty, freedom, and transformation. What many people do not realize is just how important butterflies are as pollinators of plants and food sources for other animals, not to mention their role in important scientific discoveries.
At the same time, butterflies are in trouble. Butterfly populations undergo normal fluctuations from year to year, and there can be large differences in both abundance (number of butterflies) and diversity (number of different kinds of butterflies) in any given landscape. Although these fluctuations often account for year-to-year differences, evidence is mounting that many butterflies are now declining at unprecedented rates.
The good news is that as a gardener or land manager, you can help by providing habitat and limiting the use of insecticides. When you understand why butterflies are an important part of the ecosystem and why they are currently in trouble, you can make choices in your own garden that will make a real difference in conserving these amazing creatures.
Butterflies and moths make up the second largest order of insects, the Lepidoptera, with some 160,000 recognized species worldwide. Moth species make up the vast majority of this total. Butterfly species number approximately 20,000 globally, with 800 of those in North America. Moth species number 11,000 or so in North America.
A butterfly’s wing is covered with tiny overlapping scales. These gave rise to the name Lepidoptera, from the Greek for “scaly wing.”
The name Lepidoptera comes from the Greek words lepidōtos (scaly) and pteron (wing), in recognition of the thousands of tiny overlapping scales that cover the wings much like shingles on a roof. Each scale is a single color, and collectively these scales create the complex color patterns seen on a butterfly’s wing. These scales also distinguish butterflies and moths from other insects.
Found in many different habitats, butterflies successfully live in environments from the rain forests of the equator to the northern tundra and from deserts to the highest peaks in the American West. It is no wonder that they play a role in ecosystems and have captured the imaginations of children, scientists, artists, and gardeners.
Butterflies and moths are closely related and can sometimes be difficult to tell apart. Butterflies are often thought of as brightly colored and flying by day while moths are perceived to be more muted in their appearance and fly by night. While this may hold as a broad-brush division, it is not entirely true and exceptions abound. Moths such as burnets, foresters, tigers, and ctenuchas are day flying and colorful, as are some hawk moths. On the other hand, the butterflies known as grass skippers may appear mothlike with small and fuzzy brown, tan, or dark gray bodies.
It is easier to separate moths from butterflies when they are at rest. Butterflies tend to hold their wings either partially open in a V shape or pressed together, upright over their bodies. With wings together, they can look like tiny sailboats. Most moths, on the other hand, hold their wings flat, like paper airplanes, or slightly pitched, with the forewings over the hind wings, covering their body like a tent. Moths also tend to be stouter and hairier than butterflies. And butterfly antennae are a single filament with a clubbed, bulblike tip, while antennae of moths can be either feathery (for males) or a single filament that tapers to a point (for females).
This regal fritillary (Speyeria idalia) illustrates the basic features of a butterfly: wings held upright like a sailboat and antennae with clubbed, bulblike tips.
Male moths—such as this male luna moth (Actias luna)—have feathery antennae that help them detect female sex pheromones.
At first sight, this may appear to be a butterfly, but wings held flat give it away as a moth—a mournful thyris (Thyris sepulchralis)—and the single-filament antennae as a female.
While moths have always been known to pollinate plants, the role of butterflies as pollinators has been debated. But now a growing body of evidence suggests that counter to what many researchers have long believed, butterflies are significant pollinators of at least some plants.
Butterflies are known to pollinate some types of flowers. Pollen is clearly visible on the legs of this obscure skipper (Panoquina panoquinoides).
For plants, pollination—the sharing of pollen among their own flowers or with those of other plants—is an essential step in producing seed and reproducing. Plants, however, cannot move about in order to accomplish this transfer. Approximately 20 percent of flowering plants release and receive their pollen on the wind; grasses are a primary example of wind-pollinated plants. But the vast majority of flowering plants (the other roughly 80 percent) rely on animals, mostly insects, to move their pollen from flower to flower.
For some animals, particularly bees, the pollen is a source of food, which is reason enough in itself to visit a flower. But for many other insects, as well as birds and other animals, the nourishment that draws them is nectar. Nectar is the primary food source for most adult butterflies and moths. Brightly colored flowers or heady fragrances advertise the presence of nectar, and special color patterns and markings help direct the pollinators quickly to their reward. While moving around and feeding, the animals inadvertently pick up pollen grains, which they transfer to other flowers of the same plant species. Plants can help ensure that just the right pollinator visits their flowers by hiding nectar deep within the flower; in this way they also ensure that the visitor seeking that nectar contacts the pollen in just the right way.
Numerous birds pollinate: hummingbirds in the Americas, sunbirds in Africa, honeyeaters in Australia and the Pacific islands. Mammals are also known to pollinate plants. Several species of bats pollinate trees in the tropics, and others pollinate saguaro cacti in the deserts of the southwestern United States. Non-flying mammals that pollinate include sugar gliders in Australia and lemurs on Madagascar; those lemurs, at more than five pounds, may be the heaviest pollinators in the world.
The most significant pollinators, however, are tiny: bees (order Hymenoptera), beetles (Coleoptera), flies (Diptera), and butterflies and moths (Lepidoptera). Bees are by far the dominant pollinators of crops, and it is generally agreed that in temperate areas of the world bees are the most important pollinators for plants of all kinds. Flies are more important for pollination in high-elevation and high-latitude regions, while beetles are more important as pollinators in tropical and equatorial areas, and are major pollinators of rain forest trees.
Which brings us to butterflies. Although not as centrally critical for pollination as bees are, moths and butterflies do play a significant role in the pollination of flowering plants. Plenty of established evidence indicates that moths can be important pollinators, but some have questioned whether butterflies are pollinators at all. Butterflies certainly pick up pollen when visiting flowers for their nectar; grass skippers have been observed carrying pollen, and in photographs pollen can clearly be seen on the legs and bodies of skippers. Skippers may well be important pollinators of prairie areas, since their short legs and stout hairy bodies lend themselves to moving pollen from flower to flower. Similarly, monarch butterflies (Danaus plexippus) may be seen with pollinia—small bundles of pollen—hanging from their legs, picked up from the milkweed flowers they visit.
The six-spot burnet (Zygaena filipendulae) rests on a fragrant orchid (Gymnadenia conopsea), one of several European orchids that are adapted for pollination by moths.
For any animals to be successful pollinators, they must carry pollen from the flower of a particular kind of plant to another flower of the same kind. Bees are efficient pollinators in part because they demonstrate considerable flower constancy, moving consistently among flowers of the same species and even returning again and again to a single species in separate foraging flights to gather more pollen. Although butterflies show less constancy to flower species, they are consistently drawn to flowers from which they can efficiently get nectar. Butterflies and moths may not be as effective as bees at moving pollen and thereby pollinating plants, but even so, it has been documented that many plants benefit from the pollen transfer they accomplish.
In North America, the western prairie fringed orchid (Platanthera praeclara) is pollinated by several species of hawk moths in Midwest prairies; the mountain parnassian butterfly (Parnassius smintheus) pollinates Senecio and other yellow flowers in the daisy family in montane areas of the western states and northward through Canada into Alaska; and in the meadows and forests of the Pacific Northwest, swallowtail butterflies (Papilio species) are pollinators of the Columbia tiger lily (Lilium columbianum). In Central America, the firecracker plant (Russelia species), a shrub with vibrantly colored flowers, is pollinated by the orange-barred sulphur butterfly (Phoebis philea); the shrub’s weeping branches cause its flowers to hang in a way that makes the flowers difficult for other insects to pollinate.
Europe also has a number of plants, in particular orchids, that are pollinated by Lepidoptera. The fragrant orchid (Gymnadenia conopsea) and the closely related short-spurred fragrant orchid (G. odoratissima) are both pollinated by owlet and forester moths. The greater and lesser butterfly orchids (Platanthera chlorantha and P. bifolia) may be misnamed, as owlet and hawk moths are their most frequent visitors. Each of these orchids produces copious amounts of nectar, unlike the pyramidal orchid (Anacamptis pyramidalis)—which doesn’t produce any, and which still somehow attracts enough butterflies and moths to achieve adequate pollination.
Another example of butterfly-pollinated flowers comes from the fynbos shrublands of South Africa’s Cape Province. What makes this instance most notable is that one butterfly, the Table Mountain beauty (Aeropetes tulbaghia), is the pollinator of a group of about fifteen unrelated but visually similar flowers; such dependence on a single species of pollinator is rarely found in plants, let alone in a group of different species. These flowers all bloom in late summer and have large red flowers with straight, narrow nectar tubes; the butterfly appears to be attracted primarily to the red color of the flowers, while the nectar tubes discourage birds that would otherwise visit red flowers. At least one of these species, the rust red orchid (Disa ferruginea), does not offer nectar but instead, in order to attract the butterfly, mimics species that do.
Butterfly-pollinated plants often display a similar set of features. They tend to bloom during the day and to provide nectar at the bottom of a long, narrow tube or spur. The flowers, growing singly or clustered together in a group, often have a sweet odor and typically provide a large enough surface for a butterfly to land on. The flowers are also in colors that butterflies can see, usually red through violet and often ultraviolet. To make it even easier for butterflies to find the nectar (and thus further aid the plant’s reproductive success), some plant species have evolved nectar guides—colorful lines or markings on the flower that help direct the pollinator to the nectar. In some cases, these nectar guides contain ultraviolet patterns that only particular flower visitors can see. Flower species with nectar guides are more frequently visited by pollinators than those without guides.
The Table Mountain beauty (Aeropetes tulbaghia) is the pollinator of a group of about fifteen unrelated but visually similar red flowers.
Butterflies and their caterpillars are a very important food source for many types of birds. This willow warbler (Phylloscopus trochilus) has a beak full of caterpillars, likely to feed its young.
One thing to remember as you plant and nurture your butterfly garden is that some of the animals you are providing for will be eaten by other larger animals. While we have yet to measure the full importance of butterfly populations as a food source, they undoubtedly play an integral role in providing sustenance to a variety of life on the planet. Many birds and lizards, as well as spiders, dragonflies, and other invertebrates in your garden, eat butterflies and moths. Try not to be too concerned, as this is part of nature. The fact is that if the population of butterflies is healthy, they can withstand this predation. If you see predation, it means you are providing for a robust population of butterflies and moths and that they in turn are feeding other necessary creatures. You are not just gardening for butterflies; you are providing for a wider ecosystem.
Birds are an important predator of butterflies, particularly in the caterpillar stage. Warblers and other songbirds seek out caterpillars to sustain the high energy levels required to complete their spring migration. Songbirds would not survive without invertebrates—including butterfly and moth caterpillars—to feed their young. Parasites also feed on caterpillars. Some wasps and flies lay their eggs on top of or within a caterpillar; after hatching, the parasitic larvae burrow into the host and slowly eat it from the inside, eventually killing the caterpillar and emerging as adults. Stink bugs search for caterpillars in foliage, stabbing their prey with strawlike mouthparts and dissolving the tissues so they can suck up a nutrient-rich soup, and wasps and hornets sting and immobilize caterpillars to be brought back to the nest. Ground beetles and tiger beetles prey on both caterpillars and adult butterflies, using speed and enormous mandibles to capture their prey. Small mammals such as mice, chipmunks, and ground squirrels also dine on caterpillars. Beyond caterpillars, pupae undoubtedly serve as food to many of the same predators, but observations of pupal predation are not as common.
Adult butterflies are important food for many animals including bats, lizards, birds, and frogs, as well as spiders. Dragonflies and robber flies snatch butterflies midflight, while praying mantids, ambush bugs, and flower spiders lurk among blooms to seize butterflies when they land. Sometimes a predator catches only wing fragments; in fact, you may find a butterfly with a noticeable triangular, beak-shaped wedge missing from its hind wing.
Even humans can be considered butterfly predators. People in many countries eat pupae and larvae of moths, although here in North America we may be most familiar with caterpillars as “food” in the form of the agave worm in a tequila bottle.
Caterpillars are voracious eaters. Some are large and obvious, such as this tetrio sphinx (Pseudosphinx tetrio) caterpillar, while others are noticeable only by the chewed leaves.
When growing a butterfly garden, you need to be prepared to have some plants chewed and eaten since more than 99 percent of all moths and butterflies feed on plants. The goal is to put plants in the landscape that butterflies will lay their eggs on and that will in turn be consumed by caterpillars. Caterpillars are voracious eaters, and as herbivores they are critically important to the transfer of energy through the food chain. Not only do they make energy harnessed by plants available to higher organisms by becoming food for other animals, they also return nutrients to the soil through their abundant excretions (known as frass).
Because of their voracious appetites, caterpillars are helpful in controlling plant populations. Some species are even being used as biocontrol agents for controlling noxious invasive weeds; for example, in the western United States tansy ragwort (Senecio jacobaea), a threat to farmers due to its livestock toxicity, is being controlled with the cinnabar moth (Tyria jacobaeae).
Aristotle called butterflies psyche, Greek for “soul.” This name lives on in the name Glaucopsyche, a genus in the gossamer-winged family that includes the silvery blue, Glaucopsyche lygdamus.
The beauty and brilliance of butterflies have captured the imaginations of countless people throughout the ages. Artistic depictions of butterflies appear in 3500-year-old Egyptian hieroglyphs, and ancient Hopi, Mayan, and Aztec cultures often represented butterflies in their drawings and figures. Ritual butterfly dances and ceremonies were performed by several ancient cultures. Aristotle gave the Greek name psyche (soul) to butterflies, and the butterfly has come to represent the human spirit.
Many different cultures have come to view butterflies as the souls of the dead. This is true in Mexico, where monarch butterflies return just before the Day of the Dead celebrations, and was true in seventeenth-century Ireland, where white butterflies were thought to be the souls of deceased children and where the killing of these butterflies was prohibited. Literature from the Bible to Shakespeare and from poetry to music lyrics makes many references to butterflies and moths. The renowned lepidopterist and novelist Vladimir Nabokov exquisitely shared his experiences with these animals in his autobiography, Speak, Memory. Numerous artists, including Salvador Dali, have depicted butterflies.
Europe during the Victorian era saw intense interest in collecting butterflies. Old World explorers would travel across the globe searching for new and unknown butterflies, while close to home young children and men and women alike would go on daytime collecting trips in the fields outside town. These vast collections contributed not only to the interests of the day but also to a scientific legacy.
Today, butterflies are widely used in art and jewelry. They are mounted in frames, embedded in resin, displayed in bottles, laminated in paper, and used in mixed media artworks and furnishings. British artist Damien Hirst uses butterflies in hugely controversial pieces of modern art, from collaging hundreds of individuals in kaleidoscopic paintings to releasing thousands of pupae and adults into stark white rooms to live out their short lives among museum visitors. Images of butterflies are commonly used in advertising and labeling, often to represent something natural or environmentally friendly; small monarch icons now grace U.S. foods that are certified gmo-free.
Butterflies mean business and an income source in some developing countries. Butterfly farms earn income from visiting tourists as well as from selling chrysalises to butterfly houses.
A recent study suggests that people in the United States value monarch butterflies (Danaus plexippus) as much as they do endangered whooping cranes.
Beyond the ecosystem and aesthetic value of butterflies, they are important economically. Butterfly watching generates millions a year for local communities. In places like the monarch overwintering grounds of Mexico, tourists are drawn by the thousands to a handful of towns, adding to the local economy through purchases of food, lodging, tours, transportation, gifts, and other memorabilia. Other Lepidoptera hot spots include Valley of the Butterflies on the Greek island of Rhodes, where the Jersey tiger moth (Euplagia quadripunctaria) aggregates every summer, and the Maolin Ecological Park in Taiwan, which hosts up to a million overwintering purple crow butterflies (Euploea species) each year. In tropical regions around the world, eco-resorts are now being developed that offer tourists chances to see spectacular equatorial species. Costa Rica alone has more than 2500 species of butterflies, and Peru boasts 3500 or more. In the past, butterfly tours were tailored to collectors, but as interest grows in watching butterflies rather than collecting them, more tours are being offered simply to watch butterflies in their natural habitats.
Public butterfly houses and gardens at museums, arboretums, and botanic gardens also attract visitors from around the world. Butterfly World opened in Florida in 1988, and since then additional sites have opened in Georgia, California, Colorado, and elsewhere. Natural history museums often include some sort of butterfly house or butterfly garden for visitors to experience butterflies from faraway lands. The Smithsonian National Museum of Natural History in Washington DC has a year-round butterfly garden and exhibit, and the California Academy of Sciences in San Francisco boasts a three-story living rain forest complete with free-flying birds and butterflies.
A niche market in the home gardening world has opened up to provide plants labeled to inform gardeners that these species are best for attracting butterflies. These same plants are often attractive to hummingbirds and bees as well.
In developing countries, sustainable butterfly farming, in which small farms provide specimens of adults to collectors and larvae to butterfly houses, is a source of income for some people. Papua New Guinea took this to new levels when the national government designated insects a national resource and included butterfly farming in the country’s village economic development plans. In rural villages where people have few opportunities to make a living, butterfly farming offers a chance to generate an income from using the land in a sustainable way.
Assigning a value to butterfly species and the services they provide is inherently difficult but may improve conservation of certain species. For example, a 2014 study suggested U.S. citizens are willing to support monarch butterfly conservation at high levels, up to about $6.5 billion if extrapolated to all U.S. households—a number in line with the public’s valuation of many higher-profile endangered species such as whooping cranes and one that suggests donations to conservation groups and monarch-friendly plant purchases could generate much-needed action to protect this species.
Butterflies are among the most studied insects; in England, naturalists have studied them for almost three hundred years. Butterflies (and moths to a lesser extent) are an extremely important group of model organisms used in biological research, including biodiversity and conservation biology studies, habitat assessments, animal population monitoring, and genetic studies. Their sheer abundance, diversity, and relatively well-documented taxonomy and biology, in addition to the ease of observing them in the field, make them ideal indicators of a healthy environment and ecosystem. Because of the generally positive public view of butterflies, they can act as flagships for the protection of a suite of other organisms that share the same habitat and are thus an important focus of conservation projects.
Butterfly collections have helped scientists and conservationists understand and protect butterflies and their habitat.
With their fascinating life cycles, butterflies and moths are used in many countries to teach children about the natural world. Their transformation from egg to caterpillar to chrysalis and finally winged adult is a wonder of nature, and butterflies can be used in the classroom to teach a plethora of other scientific lessons, including ones on migration, mimicry, and the use of intricate wing patterns and iridescence.
The study of butterflies has led to some incredible scientific theories and innovations. Research on the wing structure of butterflies led to new aircraft designs. Studies on the reflection and scattering of light by the scales on wings of swallowtail butterflies led to the innovation of more efficient light-emitting diodes (electric components that allow an electrical current to move in one direction but not the other). Monarchs, queens (Danaus gilippus), and viceroys (Limenitis archippus) sparked the study of mimicry.
Monarch butterflies are ubiquitous in North America and common garden visitors in many areas of the United States. These well-known butterflies make annual trips of hundreds or thousands of miles from summer breeding grounds to overwintering groves in California and Mexico. But despite populations still numbering in the millions, the monarch butterfly is quickly becoming a prime example of a once-common species now undergoing drastic population declines.
When monitoring efforts first began in the 1990s, an estimated half a billion monarchs made the epic flight each fall from the northern plains of the United States and Canada to sites in the oyamel fir forests north of Mexico City. An additional one million monarchs overwintered in forested groves along the California coast. Now, researchers and citizen scientists estimate that only about 50 million monarchs remain, representing a more-than-80-percent drop across North America. In the face of these declines and mounting threats from habitat loss and degradation, pesticide use, and climate change, the annual migration was declared an endangered biological phenomenon by the International Union for Conservation of Nature, and the North American population is being considered as of this writing in late 2015 for threatened species protection under the U.S. Endangered Species Act.
The fate of the monarch is uncertain, but the good news is that the governments of the United States, Canada, and Mexico are taking unprecedented collaborative conservation actions for both the summer breeding grounds (offering stands of the monarchs’ host plant, milkweed) and overwintering groves in Mexico. More than two dozen conservation, education, and research partners from across the United States have joined together to form the Monarch Joint Venture (monarchjointventure.org) to conserve the monarch migration and teach gardeners how to help. Gardeners can actively promote monarch and pollinator conservation simply by planting locally appropriate milkweed species, providing a variety of nectar sources from spring through fall, and avoiding the use of insecticides.
Monarch butterflies (Danaus plexippus) like these seen overwintering along the California coast are threatened by habitat loss and climate change.
Our lives would be greatly impoverished without butterflies and moths. As you have seen, they are of vital importance to ecosystems, inspire poetry and art, provide livelihoods, offer a window into the natural world, and bring beauty into our cities and neighborhoods. But unfortunately, the world’s butterflies are in peril. Although we know relatively little about the status of each species, the information we do have is not encouraging. Recent reports from practically every continent are now documenting unprecedented declines in a broad suite of butterflies.
The growth of San Francisco has smothered much habitat and led to the extinction of three butterflies: the sthenele wood nymph (Cercyonis sthenele sthenele), the Xerces blue (Glaucopsyche xerces), and the pheres blue (Plebejus icarioides pheres).
Studies in Europe have revealed that grassland butterfly species have declined by almost 50 percent since the early 1990s and three-quarters of the butterflies in the United Kingdom are in decline. In the United States alone, at least five butterflies have gone extinct since 1950; an additional twenty-five butterflies are listed as endangered nationwide, and four are listed as threatened. NatureServe, one of the leading sources of information about rare and endangered species, has assessed all 800 butterfly species in the United States and has found that 17 percent are currently at risk of extinction.
Most of the butterflies at risk of extinction are rare endemics—those species that have a narrow geographic range or very specific habitat requirements. However, lepidopterists across the United States are reporting that broadly distributed butterflies are also in decline. These downward trends are troubling and are being mirrored by many other groups of animals and plants. What is happening in our global landscapes to cause such alarming losses? Butterflies face a wide range of threats including habitat loss, climate change, disease, pesticides, and invasive plants. More localized threats, such as overcollecting and roadside mowing, can also have negative consequences. Chief among these threats is loss and fragmentation of habitat.
Habitat loss is the most significant factor leading to declines in butterflies. It includes both the outright destruction of habitat and the fragmentation of habitat into small, isolated patches. In urban areas the loss of wild habitat is apparent, but the fragmentation of habitat in rural areas is no less a problem. Farming and ranching practices can leave the landscape green but covered in fields that provide little for butterflies. Loss of both larval host plants and nectar sites can have a profound impact on butterfly populations and is the leading factor in the decline of most imperiled butterflies. This includes species like grass skippers that do not fly far in the landscape as well as the migratory monarch butterfly.
Habitat loss takes many forms, including conversion of grasslands and wetlands to agriculture, urban growth and sprawl, clear cutting of forests and replanting with single-species stands, and tree and shrub encroachment into meadows, which impacts meadow- and grassland-dependent species. One of the major problems with human-caused habitat loss and fragmentation is that it happens very quickly, so local species don’t have time to adapt. Natural changes, on the other hand, often occur over a much longer span of time, giving local species the chance to adjust.
Perhaps the best-known case of habitat loss leading to a butterfly’s extinction is that of San Francisco, California, a city that now almost entirely covers what was once one of the major coastal dune ecosystems in western North America. Three dune butterflies that lived only in this region are now extinct: the sthenele wood nymph (Cercyonis sthenele sthenele), the Xerces blue (Glaucopsyche xerces), and the pheres blue (Plebejus icarioides pheres). Three other butterflies, the Callippe silverspot (Speyeria callippe callippe), the San Bruno elfin (Callophrys mossii bayensis), and the mission blue (Icaricia icarioides missionensis), are now limited to San Bruno Mountain and just a few other locations south of San Francisco, the final remnant of the once-extensive San Francisco hills ecosystem.
Habitat loss is not restricted to farmland or development sites. Many landscapes provide little or no habitat for butterflies because they lack flowers and host plants.
Beyond urbanization, agriculture is the single largest component of global land use, and with 36 percent of the earth’s surface devoted to agriculture it is vital that we protect butterflies and other animals within this landscape. Unfortunately, the advent of large-scale monoculture agriculture in recent decades has led to huge declines in available habitat for our butterflies. Until recently, plants that butterflies could use for host plants or nectar sources grew within and adjacent to agricultural fields, but that has now changed. To eradicate weeds, genetically modified corn and soy in the American Midwest are sprayed with glyphosate herbicides, which unfortunately also target many beneficial plants including milkweed, the monarch butterfly’s host plant. As monarch numbers plummet, this loss of milkweed (and subsequent loss of available breeding ground) is thought to be one of the primary culprits.
Climate change may negatively impact a variety of butterflies and moths that live in alpine areas such as the mountains of Colorado.
We have all heard about the issue of climate change and how it may impact our environment. The terms climate change and global warming do not really articulate how greenhouse gases are impacting our world, and in fact these terms can be somewhat confusing. It’s true that some places are getting hotter and drier, but some are actually getting wetter or colder. In many places, the climate is just a lot more variable—cold one year, hot and dry the next, late snows or no snows at all. All of these changes impact a butterfly’s ability to survive in the environment.
We are already seeing the impact of climate change on butterflies. The Uncompahgre fritillary (Boloria acrocnema) is one of the first butterflies known to be impacted by climate change. This imperiled butterfly was protected under the Endangered Species Act in 1991, and it was the first time climate change was listed as a threat to an animal in an Endangered Species Act listing. The Uncompahgre fritillary is remarkable in that it is found only above 13,000 feet in the mountains of southern Colorado, some of the tallest peaks in the United States. Because of the harsh climate at this elevation (the summer often lasts only four to six weeks), it takes two to three years for a butterfly to complete its life cycle. Snowfields persist year-round on the north slopes, and the snowmelt provides a plentiful water supply for snow willow, the butterfly’s host plant. Unfortunately, those snowfields will likely be gone before the middle of this century, which may lead to extinction of this butterfly.
It is not just butterflies living in high mountains that may suffer. Many butterflies that reside along coastlines are already seeing habitat loss due to rising oceans and larger storm events. Even meadow butterflies may suffer as climate change alters moisture availability and dries up wet areas where these species’ host plants grow. Ongoing severe drought conditions in California that may be linked to climate change are likely causing declines in monarch overwintering populations on the California coast. Drought in Texas also impacts monarch butterflies looking for breeding sites as they fly north from overwintering sites in Mexico. Studies on the California drought found that some populations of checkerspots went locally extinct because adults could not find host plants on which to lay eggs.
Some butterflies are moving as a result of climate change. Scientists have already documented that some species are shifting their entire distribution northward or to higher elevations in order to find the habitats and resources they need to survive. What we don’t know is how many species are capable of this type of movement. Many species can survive only in certain types of habitats and are not able to fly far enough to find suitable new areas. Loss of habitat makes matters worse as butterflies often need to go farther through agricultural fields or urban or suburban developments to find new homes.
One additional problem is that some plant species are emerging earlier or later than they have in the past—and this can put them out of sync with the butterflies that use them. As some species of butterflies emerge earlier, they also run the risk of encountering frost or missing their host plants entirely.
Despite the challenges inherent in these changes, there are some success stories. The Quino checkerspot (Euphydryas editha quino), a once-abundant California butterfly that declined due to urban sprawl in San Diego and Los Angeles, has now moved to higher altitudes and even adopted a new host plant. This is the first butterfly known to science to change both its location and its host plant so rapidly, and it serves as a reminder that some species may be more resilient to climate change than we initially expected. Still, in order to make shifts like this possible, human-managed nature reserves, wild lands, and appropriate habitat corridors are becoming even more important. Without these links available, many species may have no place to go.
The use of pesticides, including insecticides and herbicides, is detrimental to a healthy community of butterflies. Insecticides, as the term implies, kill insects and can kill butterflies and moths if used where they feed. Herbicides can kill plants that butterflies depend on and reduce the amount of food available to them.
INSECTICIDES Insecticide use is now ubiquitous around the globe; more than one billion pounds of insecticides are used annually in just the United States. Insecticides are widely used in agriculture, on rangelands, in woodlands and other natural areas, in waterways, on golf courses, on residential lawns and gardens, on sports fields, along roadsides, and on street trees. Interestingly, several studies show that more insecticides are used in urban and suburban areas than in agricultural areas.
According to the U.S. Geological Survey, more pesticides are often used per acre in urban and suburban areas than in agriculture.
Many insecticides were designed to control moth pests of commercial crops, which means they can be especially toxic to butterflies. Studies have shown that butterflies in and around agricultural fields are impacted when the fields are sprayed. Even butterflies that use habitat on the edges of fields are at risk because these chemicals can drift away from the areas that have been treated. Other uses also affect butterflies. In Florida, aerial spraying of malathion and other pesticides for adult mosquito control has devastated some local butterfly populations. The Schaus swallowtail (Heraclides aristodemus ponceanus) was listed under the Endangered Species Act in part because of mosquito spraying.
A new class of insecticides called neonicotinoids is especially concerning. These synthetic chemicals are similar in structure and action to nicotine and work by blocking nerve impulses in insects and other invertebrates. Currently the most widely used group of insecticides in the world, neonicotinoids are employed broadly in the nursery industry and beyond; the U.S. Geological Survey routinely finds these chemicals in stream samples across the United States. Neonicotinoids are currently under scientific scrutiny for the potentially substantial threats that they pose to pollinators (including butterflies and moths), aquatic invertebrates, soil-dwelling invertebrates, and birds. The use of these insecticides has led to the loss of millions of honey bees in recent years, and in a single event more than fifty thousand bumble bees were killed when trees near a shopping center were treated.
What makes neonicotinoids different from other insecticides is that they have a systemic mode of action; this means they are taken up into every part of the plant including the nectar and the pollen. Neonicotinoids can also be persistent for long periods in plants and soil. They can remain in soil for months or even years after a single application, and untreated plants may absorb chemical residues in the soil from the previous year. Measurable amounts of residues have been found in woody plants up to six years after a single application.
Many products containing neonicotinoids are sold for use in gardens; some of the most common include the active chemical ingredients imidacloprid, dinotefuran, clothianidin, and thiamethoxam. What makes this especially troubling is that products approved for home and garden use may be applied to ornamental and landscape plants, as well as turf, at significantly higher rates (up to thirty-two times higher) than those approved for agricultural crops. Many scientists from all over the world have come together to call for bans on these chemicals, especially in garden situations. These insecticides should not be used in the garden if your goal is to help provide for butterflies or other pollinators.
HERBICIDES Herbicides kill plants and can impact the butterflies that depend on them. Herbicide use has eliminated milkweed from much of the Midwest farm landscape and is likely a major factor in the decline of the monarch butterfly. The key issue with herbicides is how they are applied. The broadcast application of a nonselective herbicide can kill all of the plants in an area, effectively eliminating or reducing floral resources and host plants for butterflies. If you find you must use an herbicide, it is very important to target treatments to ensure host plants and nectar sources are not impacted.
Invasive plants are a large and growing threat in our natural landscapes. These are plants that are not native to a region that have a tendency to spread out over large areas, quickly crowding out native plants. For many butterflies that have specific host plant requirements, the encroachment of invasive plants may lead to a decline in their host plant and subsequently a decline in the butterfly. Grass skippers such as the federally threatened Dakota skipper (Hesperia dacotae), which rely on specific grasses in their larval stage, are negatively impacted by invasive grasses that crowd out native species.
Invasive animals can also pose a threat. For example, the introduced green iguana in South Florida can be a major herbivore of the nickerbean, the host plant for the endangered Miami blue butterfly (Cyclargus thomasi bethunbakeri). This butterfly has a tiny population limited to only one or two sites in the Florida Keys and a nearby island. By eating the leaves of these plants, iguanas not only remove the food source for larval Miami blues, they also likely destroy eggs and larvae already on the plant.
The introduced green iguana in South Florida eats the host plant of the endangered Miami blue butterfly (Cyclargus thomasi bethunbakeri).
Over the past century, nonnative insects have been released in order to control—as predators, parasites, or herbivores—pest insects and nonnative invasive plants. This biological control is often touted as a safe alternative to chemicals and is now frequently applied. However, increasing evidence suggests that the negative impacts of such releases on nontarget, native species can be significant.
Studies in Illinois have demonstrated that lady beetles introduced to control aphids on crops also feed upon young caterpillars of monarch butterflies. Similarly, a study in Hawaii found that 83 percent of parasitoids found in native moths were species that had originally been introduced for biological control and that now parasitize a wide range of native host species. An introduced parasitic fly is also thought to be a factor in the decline of large silkmoths in the eastern United States.
Indirectly, insects released for the purpose of controlling nonnative invasive plants can affect native pollinators by reducing food availability. For example, two European weevil species released in North America to control nonnative thistles now adversely impact native thistles, limiting an important nectar source for a range of butterflies.
For many years butterflies have been released at weddings, funerals, and other events. People are thrilled by the majesty of dozens or hundreds of butterflies fluttering over these events. Although we do not know how many butterflies are sold and released each year because the butterfly-rearing industry does not give out its records, we believe that hundreds of thousands are sold, shipped across the United States, and released away from where they were raised. Unfortunately, the transfer and release of butterflies for weddings and other events may cause several problems for native butterflies.
Mass butterfly releases may spread diseases and parasites to wild populations. Mass production of butterflies makes it easy to transmit disease. Butterflies did not evolve under conditions in which they developed in large groups, and they are very susceptible to diseases that can be transmitted among larvae. Breeders are not required to follow specific disease-preventing protocols, nor do outside agencies routinely test captive stock for diseases.
Another threat of butterfly releases involves introducing unhelpful genes into local populations, which could negatively influence the survivorship potential of native butterflies. Genetic transfer can occur when released butterflies mate with wild butterflies and they produce offspring; the genetic makeup of the offspring will include traits from both the wild and reared butterfly parents. Though this threat is difficult to quantify and demonstrate, it should certainly be approached through the precautionary principle, with the burden of proof on potential releasers to prove the harmlessness of their proposed activity.
These releases also confuse studies of butterfly distribution and make it hard to prioritize habitat conservation. In order to prioritize conservation, we need to know where butterflies live, breed, and move within the environment. When butterflies are released into the environment, they muddle our ability to understand these important issues. As one example, monarch butterflies have shown up in the San Juan Islands in northern Washington State in recent years—a place where they have never been seen before. We do not know whether these monarchs made it to the islands naturally and may be expanding their range due to climate change or whether they arrived because of releases.
Another problem is that many of the animals we release die from exposure or starvation because it is the wrong time of year or the wrong locality for them to survive. If they do succeed in reproducing in the new territory, the other problems are only magnified. Treating butterflies as commercial ornaments to be grown, shipped, and released at will is not an appropriate way to increase respect and care for wild butterflies. Birds have been protected from such treatment for decades, and it is time to extend the same kind of concern to butterflies. It doesn’t harm butterflies to collect them locally and raise them for release, but captive rearing of butterflies must be done carefully. The practice of mass releases is opposed by many organizations including the Xerces Society and the North American Butterfly Association.
Other activities such as overcollecting may threaten butterflies, although this is likely only a threat to butterflies whose populations are already imperiled. Light pollution is also a concern; the lights that brighten our streets and highways at night are apparently responsible for losses of nocturnal insects, particularly large moths. Many of the threats we’ve discussed are human caused in some way, but natural threats in the form of predators, parasites, disease, and natural disasters also take their toll on butterfly populations.
Despite the many threats to butterflies and their habitats, the situation is far from hopeless. By providing pesticide-free habitat in your garden, you can be part of the solution. If enough people take action to plant flowers, provide host plants, and offer overwintering areas, butterflies will have a better future and we will have beautiful landscapes to enjoy.
