PLASTERER or POLYESTER BEES (Family Colletidae)
Family Colletidae is a large, mostly Australian family with a worldwide distribution (excluding the Arctic and Antarctic). This was once considered the most primitive family of bees, but recent molecular work suggests that the family Melittidae may be more primitive. Understanding the behavior of these primitive groups is important in understanding how bees coevolved with plants. For example, if the Colletidae are the most primitive, it suggests that early bees were generalist foragers, whereas if Melittidae are the earliest ancestors, early bees were plant specialists, that is, they fed on only specific plants, and later groups of bees evolved to become generalist foragers.
Colletidae come in a variety of shapes and sizes, but most bees in this family have a short, broad, two-lobed glossa and a short, broad labrum. They also have only one suture below their antennal socket. They are often called plasterer bees because they line and smooth the walls of their nest cells with cellophane-like secretions. Many of the bees in this family do not roll balls of pollen. Instead, they create liquid or semiliquid pollen masses on which the larvae develop. Most Colletidae are solitary and very rarely parasitic.
There are seven genera in the family Colletidae in North America: Caupolicana, Colletes, Crawfordapis, Eulonchopria, Hylaeus, Mydrosoma, and Ptiloglossa. Two are known from California: Hylaeus and Colletes.
YELLOW-FACED BEES or MASKED BEES, Genus Hylaeus
Common California species: Hylaeus modestus NATIVE
Hylaeus modestus, native
GENUS SUMMARY: Hylaeus (hi-LEE-us) is a genus that is found worldwide, with about 700 identified species. There are approximately 25 species in North America and 14 in California. The individual species tend to be widely distributed and can be very abundant locally.
DESCRIPTION: Hylaeus are shiny black, slender, hairless, and superficially wasplike bees. They are small bees, 0.2–0.3 in. (5–7 mm) long. These markings are more pronounced on the males. This group is called masked bees because of the small yellow or white diamond-shaped markings on their face.
Hylaeus do not have colored markings on the abdomen. They lack pollen-carrying scopae and instead carry both pollen and nectar internally. They have two submarginal cells in their fore wing. Under magnification, you can see the basal vein is not strongly arched at the base. The jugal lobe of the hind wing is about three-fourths as long as the vannal lobe. They have narrow slots or foveae running along each compound eye from the base of the antenna to the ocelli. The labrum is broader than it is long. Hylaeus females have one subantennal suture.
SIMILAR INSECTS: Hylaeus resemble small sphecoid wasps. Hylaeus, like all bees, have branched hairs that do not reflect light, while wasps have unbranched, light-reflecting hairs that glitter in light. You can only see these hairs under magnification. Hylaeus also resemble Ceratina but are not quite so robust or shiny.
FOOD RESOURCES: Hylaeus carry pollen and nectar in their gut, not externally, and regurgitate it upon returning to their nest. This way of carrying pollen makes it difficult to assess what flowers they visit (because pollen cannot be sampled from the bee without dissection). They are suspected to be primarily generalist foragers. Hylaeus are short-tongued, but their small body size enables them to access deep flowers. The pollen wasps, members of the genus Pseudomasaris, also carry their pollen and nectar internally.
NESTS: Hylaeus nest in stems and twigs, lining their brood cells with a self-secreted cellophane-like material. There are a few species that use preformed cavities. They lack strong mandibles and other adaptations for digging; thus, many species rely on nest burrows made by other insects.
FLIGHT SEASON: This genus has primarily spring bees though some persist into fall.
POLYESTER BEES or DIGGER BEES, Genus Colletes
Common California species: Colletes hyalinus NATIVE
Colletes hyalinus, native
GENUS SUMMARY: Colletes (koe-LEE-teez) is a widespread and common genus with approximately 460 identified species worldwide. There are 98 species in North America and 31 species from California. They range as far north as Alaska.
DESCRIPTION: Colletes are small to moderately large bees, 0.3–0.6 in. (7–16 mm) long, with a very hairy head and thorax. They have pale bands of hair on their abdomen. Their face seems to taper toward the mouth, and the eyes are slanted toward each other, making their head appear heart-shaped. They carry pollen in scopae on the upper to lower part of the hind legs. They have three submarginal cells and are the only genus with an S-shaped second recurrent vein on the fore wing, which you can see under magnification.
SIMILAR INSECTS: Colletes resemble some Andrena and Halictus, but the head of Colletes is more heart-shaped. Colletes have a curvy vein in their fore wing that also helps distinguish these bees.
FOOD RESOURCES: Many Colletes are floral specialists and may visit only a small number of plant species. The specialist bees are generally found on plants of the families Asteraceae, Papilionaceae, Hydrophyllaceae, Boraginaceae, Malvaceae, Zygophyllaceae, and Salicaceae in California.
NESTS: Most Colletes make solitary nests in the ground, and a few species nest in large aggregations. Often called polyester bees, Colletes have a unique method of lining their brood cells with a completely waterproof cellophane-like material secreted from their Dufour’s gland. The cellophane-like material does not permeate the surrounding ground; it is instead easily separable from the soil. A Colletes female completely encloses her brood cells in this waterproof membrane, thus protecting her brood from fungal attack. Colletes also secrete linalool, a fungicide and bactericide used to protect brood cells, from a gland near their mandibles. Colletes leave provisions for their young in liquid form (like Hylaeus species) and attach the egg to an upper wall of the brood cell rather than placing it on the provisions.
One species of fly, Miltogramma punctatum, is a specialist parasite on some Colletes species. It follows a female Colletes back to her nest and waits near the nest entrance for the bee to leave. The fly then enters the nest and deposits its egg in a Colletes cell. The fly egg soon hatches, and the fly larva eats the pollen and nectar in the cell, causing the newly hatched Colletes larva to starve.
FLIGHT SEASON: This genus has a mix of spring and fall bees. There is even one species group that produces two broods a year, one in spring and one in fall.