We studied worker longevity in two colonies of Bombus fervidus (F.) and two colonies of Bombus pennsylvanicus (De Geer). In 1981, adult life expectation for B. fervidus workers was 21.8 days. In 1982, mean expectation of life at adult emergence was 34.1 days for workers of B. fervidus and 33.0 days for workers of B. pennsylvanicus. The longevities observed in 1982 are the highest yet recorded for temperate bumble bee species, and are intermediate between the previously described extremes of short life-span in north temperate species and high longevity in a tropical species. This study suggests that bumble bee life expectancy tends to decrease as one progresses northward. However, variation in life expectancy within B. fervidus at a single location in two consecutive years was almost as great as previously described differences in longevity between tropical and temperate species. Shortened life-span may therefore be associated with increased intensity of foraging activity during periods of low forage availability as well as with latitude. In both years, survivorship of late-emerging worker cohorts was consistently low, possibly because a larger proportion of late-emerging workers become foragers.

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