Birkmann's Cellophane Bee
Size: 12 mm (female)
9-10 mm (male)
Associated plants at NBC:
Plant Family: Euphorbiaceae
Plant Family: Asteraceae
October & November 2019
A female Birkmann's cellophane bee (Colletes birkmanni)
A male Birkmann's cellophane bee (Colletes birkmanni)
Birkmann's cellophane bee (Colletes birkmanni) is a medium-sized bee with a dark abdomen boldly striped with white hairs. The female bee shown here has thorax hairs that are a light rust color; a face covered with white hairs; and a dark abdomen with bold white stripes. The male bee is much paler: it has exuberant white hairs on its face and thorax and white abdominal stripes.
According to Jack Neff, Director of the Texas Melittological Institute, Birkmann's cellophane bee is common in south Texas. Nonetheless, there has been little written about its nesting behavior or biology. Neff reports that the species is bivoltine -- that is, there are two crops of of the bee each year, with fall and spring generations. Birkmann's cellophane bee is a generalist pollinator commonly found feeding on plants in the family Asteraceae.
The female bee shown here is the single specimen of this species documented at the National Butterfly Center in 2018. The bee was discovered in November of 2018, near an irrigation canal, feeding on woolly croton. A year later, both male and female bees were found foraging on seaside goldenrod in the front garden of the National Butterfly Center.
Swenk's Cellophane Bee
Size: 11 mm (female)
Food plants at NBC:
Plant Family: Solanaceae
When seen: April 2019
A female Swenk's cellophane bee (Colletes swenki)
Purple groundcherry (Quincula lobata)
Plants of the family Solanaceae, such as tomatoes, eggplants, peppers, tomatillos and nightshade, require a special form of pollination called "buzz pollination." In such plants' flowers, pollen is packed tightly into the anthers, so that they need to be turned upside down and shaken for the pollen to be released.
Some bees, such as bumblebees and some leafcutters practice "buzz pollination," vibrating their wing muscles in order to shake pollen loose from plant anthers. Swenk's cellophane bees are capable of buzz pollination and thus of pollinating purple ground cherries, which belong to the Solanaceae family.
Only a handful of bee species are documented pollinators of this native Texas plant. Among these are the two very similar cellophane bees, Colletes texanus and Colletes swenki. Within the United States, these species are found primarily in Texas.
Unlike the autumnal Birkman's cellophane bee shown in the previous entry, Swenk's cellophane bees appear at the National Butterfly Center in spring. Swenk's cellophane bees are documented pollinators of spring-blooming mesquite and other pea-family plants.
Bees of the genus Colletes line the cells of their nests with a waterproof material which, when dry, resembles clear plastic. Accordingly, they are sometimes called “cellophane bees” or, alternately, “polyester bees”. Cellophane bees are equipped with unusual forked tongues, which they use to paint the plastic-like material onto their nest walls in order to keep their nests dry. The bees produce the material from a special abdominal organ called the Dufour’s gland, named after French naturalist Léon Jean Marie Dufour, who first recorded his fascination with the bees’ fabrication of plastique in 1835.
According to the Xerces Society's Guide to Attracting Native Pollinators, cellophane bees also spray their egg-cell walls with a natural fungicide and bacteriacide, linalool, secreted from a gland in the bees' mandibles. After coating their cells, the bees fasten their eggs onto the cell walls rather than leaving them on nest floors where moisture might collect. The bees provision their cells by mixing pollen and nectar together to make a liquid “bee bread” for their offspring; these provisions are stored in cellophane sacs that look a little like elongated plastic sandwich bags. The special measures taken by the bees to protect their eggs against water and fungus allow them to build nests near stream banks and other areas with wet soils.
Cellophane bees are solitary. They construct individual nests in the ground, excavating tunnels that exit through small round holes. Despite their solitary status, the bees tend to build their nests near one another. Groups of nesting cellophane bees sometimes number into the tens of thousands. These bees, however, are non-aggressive and do not form swarms. They are important pollinators of spring trees, crops and wildflowers.
The nests of cellophane bees are parasitized by cuckoo bees in the genus Epeolus, which are sometimes called "cellophane cuckoo bees". Epeolus bees sneak into the egg chambers of cellophane bees and deposit their own eggs there. When the cuckoo larvae hatch, they kill off the cellophane bee young and eat the food stores left by the mother cellophane bee for her own offspring.
Cellophane bees are about the size of honey bees (or slightly smaller or slightly larger). They are hairy, with pale, light-brown or rust-brown thoraxes and dark abdomens striped with bands of pale hairs. The faces of cellophane bees are heart-shaped -- that is, a cellophane bee's eyes slant toward one another, and its head tapers downward toward its jaw. Cellophane bees' faces are usually covered with pale or light-brown hairs, and their antennae are medium-length. Female cellophane bees carry pollen on the upper parts of their hind legs.
Species identification of cellophane bees often hinges on such traits as size; geographic location; the color of hairs on a given bee's thorax and head; the narrowness vs. wideness of the basitarsus of the bee’s hind leg; and the appearance of the bands of pale hair on the bee's abdomen.
The period in which cellophane bees appear, as well as their feeding habits, can aid intheir identification as well. For example, Birkman's cellophane bee emerges at the National Butterfly Center in the fall.
Two species of Colletes bee have been documented at the National Butterfly Center: Birkman's Cellophane bee and Swenk's cellophane bee. More detailed information on these species is provided below.
TAXONOMY OF CELLOPHANE BEES
Species shown here: