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Science and Innovations

Earth Notes: The Decline Of Western Bumble Bees


Of thirty known bumble bee species in the western U.S., the bombus occidentalis – the western bumble bee - is among the most common. But their numbers are drastically declining.

Over the last two decades, these yellow-and-black furred insects have experienced a 90% drop in abundance across the West. That’s according to research by Jonathan Koch , an entomologist at the U.S. Department of Agriculture in Logan, Utah. His data adds to a growing body of research with the same alarming findings.

Western bumble bees perform critical pollination services for wild plants and cultivated fruits and vegetables. They are known as “buzz” pollinators – attaching to a plant’s pollen structure and vibrating their wings to release it. Many plants, including tomatoes and peppers, require this technique to spread their pollen.

These bees live in colonies and nest in the ground. They are known to forage along streams, in canyons and meadows and sometimes in burned areas. They are well adapted to cold, and overwinter in small underground cavities.

Several intersecting reasons are suspects in their decline, including altered habitat and loss of nest and hibernation sites, insecticides and climate change. Wild populations may also have been infected with disease spread by commercially raised bees.

The U.S. Fish and Wildlife Service is now reviewing the western bumble bee for possible listing under the Endangered Species Act. In the meantime, citizen science groups like Bumblebee Watch are helping document the lives of these once-common pollinators.