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Earth Notes: Bumblebees, and the Flowers They Fit

Insects and the plants they pollinate have evolved to fit like a key and a lock. 

Bumblebees perform critical pollination services while they feed on the nectar of flowers. But recently researchers have detected a mismatch between them and their flowers, most likely because of climate change.

Using microscopes, researchers measured the millimeter differences in tongue lengths of two alpine bumblebee species in the Colorado Rockies--one with a longer tongue and one with a shorter tongue. They looked at current specimens and others collected from 1966 through 1980 and housed in museums.

Tongue length is a telling trait because it determines the type of flowers these bees feed on. Longer tongues mean they can dip deep into tubular flowers, like skypilot. Shorter tongues let them generalize among flowers, and visit shallower blossoms like bluebells.

With nearly a half-century of data, the researchers have seen a surprising trend. Average tongue lengths of both long- and short-tongued bees have declined by a one-fourth. In evolutionary terms, that’s a rapid change.

They think the shift is probably related to earlier snowmelt and warmer summers in the mountains. That has meant fewer flowers overall, and thus less food for bumblebees. Being less choosy means the bees have more chances to find nectar, and spend less energy getting it. So it’s bees with shorter tongues that have survived and reproduced.

Looking into the future, the next big question is whether flowers will adapt to a changing climate in lockstep with their insect partners.

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