Apidae: Bumble Bees (Bombus spp.)

Biology

Very familiar, easily recognized and charismatic bees! Most common in higher latitudes of the northern hemisphere, there are less than 50 species of bumble bee in North America and many are in decline. Robust, stout and very hairy moderate to large-sized bees (0.4-1.0 inches long). They have yellow, black, white, brown or orange bands which help to characterize different species, although much color variation occurs even within a species.

Bumble bees nest in colonies that are initiated by a single female (queen) in the spring. Nests are eusocial where a division of labor occurs among the female offspring along with cooperative brood care. At the end of summer most bumble bees die leaving only a few mated queens to hibernate, usually underground. Bumble bee nests consist of an irregular cluster of ball-like, wax brood cells constructed in a small cavity like an abandoned rodent burrow. The queen stores nectar in her crop after visiting flowers, regurgitating it when she returns to the nest. Some nectar is also combined with pollen to form a pollen ball. She lays a batch of about a dozen eggs on top of the pollen ball that then feeds the hatching larvae. Eggs laid early in the season produce female offspring that forage leaving the queen to continue pollen ball construction and egg-laying during summer. Male offspring are produced in late summer to mate with new females that overwinter and become queens the following season.

Bumble bees often forage in the same patch of flowers for many days, until nectar and pollen availability decline. Another feature that characterizes bumble bees and makes them important pollinators is their ability to ‘buzz-pollinate’. They do this by disengaging their wings from flight muscles which then shake their entire body at a frequency close to the musical Middle C note. This airborne vibration increases the release of pollen from flowers of a number of important crop plants including tomato, peppers, blueberries and cranberries.

There are 29 bumble bee species in Washington, and while many are localized and uncommon, at least half a dozen species are frequent visitors to backyards in both eastern and western Washington.

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