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
This is a female Birkmann's cellophane bee. 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.
Note that the hind-leg basitarsus of this female Birkmann's cellophane bee is long and narrow (3 3/4 as long as it is broad). The yellow material on the bee's feet is pollinia (pollen clusters) from flowers. (The basitarsis is the second long segment from the top shown in this picture).
Both males and females of this species may have rust-colored thorax hairs. Other individuals of this species with much paler thorax hairs have appeared at the butterfly center.
A male Birkmann's cellophane bee
A male Birkmann's cellophane bee: All of the hairs on the bee are light-colored.
Alternate view of male bee
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. In November 2019, both male and female bees were found foraging on seaside goldenrod in the front garden of the National Butterfly Center.
Food plants at NBC:
Plant Family: Solanaceae
When seen: April 2019
Swenk's Cellophane Bee
Size: 11 mm (female)
A female Swenk's cellophane bee (Colletes swenki)
A female Swenk's cellophane bee gathering pollen from purple ground cherry
Purple ground cherry: this low-growing plant has five-petaled flowers about the size of quarters. It belongs to the same family as tomatillo, and like that garden plant, purple ground cherry produces fruit wrapped in papery husks.
Note the the basitarsus of the bee's leg (the second segment below the knee) is neither particularly wide nor particularly narrow. Basitarsis width is a trait that aids in identification of Colletes species.
Face of the female bee
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 swenki and (texanus).
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.
Texas Cellophane Bee
Colletes texanus texanus
Size: 7-8 mm (male)
9 mm female
Downy Ground Cherry
A male Texas Cellophane bee on physalis
A male Texas cellophane bee.
This is a small Colletes -- it measures approximately 7 mm.
Pale and gray hairs cover the bee's thorax and vertex (the top of the head). The bee's hind basitarsis is narrow. Its tegulae (wing nodes) are black, and the white bands on its abdomen are narrow and well-defined.
The bee and other similar males were found feeding on downy ground cherry, a plant of the nightshade family, Solinaceae, which requires buzz pollination.
Colletes texanus was named by entomologist Edward Townsend Cresson in 1872, whose description of the species wa based on a female bee he found in Comal County. Within the United States, the Texas Cellophane bee is found nearly exclusively in Texas. It has been documented in recent years in Cameron, Dallas, Hidalgo and Travis Counties.
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:
A cellophane bee peering from its nest hole
An aggregation of cellophane bee nests
The heart-shaped face of a cellophane bee
An Epeolus cuckoo bee: this genus parasitizes the nests of cellophane bees.