PULLMAN (AP) — Winter is a tough time for bees at the Washington State University Teaching Apiary.

In addition to frigid temperatures, honey bee colonies must battle disease and parasites. WSU researchers work to help bees fight off these threats and survive until spring.

When outside temperatures fall below 55 degrees, bees form a "winter cluster," packing tightly together and vibrating their wing muscles to keep warm.

Humans ensure that every hive is raised off the ground and every entrance angles downhill to drain rainfall and prevent rotting. They also install wire mesh screens in the entrances to ensure mice can't come inside.

WSU entomologists keep more than 200 hives on the Pullman campus and on surrounding properties in Washington and Idaho.

Bees are the world's most important pollinators.

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