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Bumble Bee Biographies

Bumble Bee Biographies

Genus Bombus (bumble bees)

True bumble bees

The genus Bombus is divided into "true" versus "cuckoo" bumble bees. The latter belong to the subgenus Psithyrus and are covered below.

True bumble bees spend the winter as solitary mated queens that become active in spring. First, in April or May (depending on species), each queen seeks out her nesting site. This can be underground, at the surface level, or well above ground, but abandoned mouse nests (underground) seem to be preferred. Second, she constructs a wax honey pot in which nectar is stored (this is needed especially during periods of inclement spring weather), and she visits blossoms of early-flowering plants such as willow, where she gathers pollen and nectar to feed her offspring. Third, she constructs a wax egg cell, into which she begins laying eggs. The eggs hatch into larvae, which spin cocoons and enter the next stage (pupa) within only one week. Finally, from these pupae, adult bees emerge; these are the first workers of the colony. Once the workers emerge, they do all of the foraging flights to visit flowers. The queen's sole duty from then on is to lay more eggs, and she never leaves the nest again.

There are two modes of feeding larvae: in pocket makers, pockets of wax are constructed alongside the larvae, and returning workers drop pollen into the pockets. In pollen storers, pollen is stored remotely from the larvae, and nurse bees take pollen to the larvae, transferring it via their mouths (regurgitation). In some species, however, only those larvae that are destined to become workers are fed by the pocket method, whereas those that will become queens or males are fed via regurgitation. And, within female larvae, queen versus worker caste can be determined by differential feeding.

In late summer, males and new queens are produced, and the old queen dies. New queens and males undergo mating flights, but the males and workers die off by winter. Only the mated new queens survive the winter, to begin the cycle anew during the following spring.

On this site, we have tried to emphasize color as the main basis for identifying bumble bees, because color is the most likely character to be visible in the average photograph of a bee. People who study bumble bee classification, on the other hand, make their observations from preserved specimens, and this allows close-up examination of fine structural characters such as number of "segments" in the antenna, size and location of the simple eyes, and shape of the "cheek" area of the "face" of the bee. Size in bumble bees usually is indicated by giving the length of the radial cell (a "cell" in any insect wing is an area of wing membrane that is outlined as a clearly separate area by one or more of the wing veins). In bumble bees, the radial cell lies along the front edge of the wing just beyond mid-length. Apparently, this cell is proportional to overall size of the bee, i.e., a large bee will have a longer radial cell than will a small bee.

Nine species of true bumble bees occur in Illinois:

Bombus affinis (the rusty-patched bumble bee)
Bombus auricomus (the black and gold bumble bee)
Bombus bimaculatus (the two-spotted bumble bee)
Bombus fervidus (the yellow bumble bee)
Bombus fraternus (the southern plains bumble bee)
Bombus griseocollis (the brown-belted bumble bee)
Bombus impatiens (the common eastern bumble bee)
Bombus pensylvanicus (the American bumble bee)
Bombus vagans (the half-black bumble bee)

Cuckoo bumble bees

Cuckoo bumble bees (hereafter, CBB) are externally similar to true bumble bees (and often are mistaken for them), but they can be differentiated by the absence of a pollen basket on the hind leg (in females), and by the more sparse covering of hair on the upperside of the abdomen. As in true bumble bees, solitary mated CBB queens hibernate throughout the winter and become active during the spring. The new CBB queen typically becomes active somewhat later in the year than does the true bumble bee queen, the reason being that, instead of initiating its own colony, the CBB queen needs to find an already-established colony of true bumble bees. Once that is done, she enters the true bumble bee colony, kills all of the eggs, larvae, and pupae of the existing colony, and lays her own eggs. Her brood will be taken care of by the true bumble bee workers; no CBB workers are produced. This parasitic strategy, which is superficially reminiscent of that of the cuckoo bird in the nests of other bird species, is the basis of the common name of this group of bumble bees.

After the colony is parasitized by the CBB, the true bumble bee queen remains in the nest, but she stops laying eggs, and the colony eventually dies off without producing males and new queens as it usually would. Some species of true bumble bees are more prone than others to parasitization by CBB. One species, the fiery bumble bee (Bombus fervidus), apparently is able to ward off CBB by covering the invading queeen with honey. In uncommon instances, CBB even try to parasitize species other than true bumble bees. For example, Plath (1927) reported an unsuccessful attempt by a CBB to enter a honey bee colony.

Two species of cuckoo bumble bees occurr in Illinois:

Bombus citrinus (the lemon cuckoo bumble bee)
Bombus variabilis (the variable cuckoo bumble bee)

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