Helping wild bumblebee queens overwinter

By Laura Johnson, extension pollinator support specialist, UVM

Wild bees are important pollinators for our crops, gardens and wild plants. In Vermont there are over 350 types of wild bees, including 17 different species of bumblebees.

Bumblebees are efficient pollinators that are especially important for spring crops, such as early blooming berries and tree fruits. But by late fall, a colony that may range in size from 50-500 bees will have all died except for a single new queen.

As with all bees, the queens depend on pollen, nectar, clean water and safe nesting sites for survival, all of which are limited resources in our managed landscapes. In addition, there is strong competition among species for these resources.

Queen bees will be one of the first visitors of spring crops, hungry after a long winter. To help them survive the winter, here are some things gardeners and landowners can do.

• Leave blooms standing until the first hard frost. To gain enough body mass for winter survival, bees require a lot of pollen and nectar. Leaving plants up as far into the fall as possible, ideally until they are killed by frost, provides a good source of both.
• Established rodent burrows are known nesting sites for bumblebees. Maybe all those voles tunneling through your landscape have a saving grace?
• Consider reduced mowing and avoid cutting back ornamental bunch grasses. Don’t rake up fallen leaves, and skip the winter brush pile burn party. All these provide great rodent burrow materials and locations where bumblebee queens can nest during winter months.
• Man-made structures can also become wild habitat. Whether it’s your 1800s stone wall reminiscent of New England sheep farming, an old foundation or your new $30,000 retaining wall, each provides protective cracks and crevices where bumblebees can find shelter.
• Consider conserving historical structures on your land. Or cultivate new habitat by taking rocks picked from your property to make a rock pile where bumblebee queens can nest as they enter diapause, a state of dormancy, for the winter.
• Offering pollen, nectar and water sources late into the fall and abundant and diverse undisturbed shelters for nests will help ensure each queen’s survival and early season pollination services next spring.