A bumble bee flying from flower to flower is a common sight in the summer landscape. These large, fuzzy bees are sometimes called the teddy bears of the bee world because of their hairy bodies and bumbling flight patterns. North America is home to 45 species of native bumble bees, with about a dozen species seen in Ohio. These bees play an important role as pollinators of crops and wild plants.
Bumble bees are sometimes confused with carpenter bees, particularly in the spring when both species are active and of a similar size. Bumble bees have hairy abdomens and heart-shaped faces, while carpenter bees have shiny abdomens and wide, round faces. Bumble bees do not nest in wood, bore holes in wood structures, or hover menacingly as do male carpenter bees near nesting sites.
Bumble bees are social bees that live together in a colony. Each colony is active for only one year, with new colonies started each spring by a new queen bumble bee. This differs from honey bees, which have a perennial colony that survives from year to year.
In early spring, each overwintering bumble bee queen must find a suitable home for her colony, commonly in an abandoned rodent burrow or sometimes directly on the ground, depending on the species. Sometimes, bumble bees will nest in unused straw or hay bales, unturned compost piles, upside down clay pots, at the base of bunch grasses, in bird houses or feeders, or in crevices in rock walls.
Once she finds a nesting site, the queen secretes wax to create comb and then lays about a dozen eggs. She mated with a drone last fall, and has reserved the sperm in a special organ in her abdomen. Using the heat generated by vibrating her flight muscles, the queen keeps the eggs warm. When the larvae hatch, they eat pollen and nectar that the queen has collected. The queen continues to keep the nest warm and collect food for the developing larvae. About two weeks later, the larvae pupate, then emerge in about another two weeks as adult workers.
Worker bees, all females, are much smaller than the queen, particularly early in the season. They take over the work of tending and guarding the nest and bringing pollen and nectar back to the colony. Female bumble bees transport pollen on a flattened section on their hind legs called the corbicula.
The queen continues to lay batches of eggs throughout the summer, rarely leaving the nest. Toward the end of summer, the queen lays unfertilized eggs that will become male drones, and other fertilized eggs that will be reared as new queens. The new queens and drones leave the colony to mate with other bumble bees of the same species. In most species, queen bumble bees will only mate once.
Newly mated queens feed on flowers to pack their bodies full of fat to survive the winter. Each queen will spend the winter burrowed about 10 inches below ground, emerging in spring to start a new colony. All the members of the old colony die with the winter’s cold, including the old queen, and all workers and drones.
Unlike many other bees, bumble bees can forage for food in cool, wet conditions and in low light. This makes them important pollinators of plants that bloom in early spring or grow in shady conditions. Their robust bodies help them fly far from the nest in search of food—sometimes more than a mile if food is scarce.
Bumble bees are key pollinators of crops such as apples, cucumbers, squash, raspberries, blueberries, and greenhouse tomatoes. They are also essential pollinators of many native plants, and in some cases serve as the only pollinator able to pollinate certain native plants.
Bumble bees can do something only a few other species of bee can: an action called buzz pollination. Blueberries, cranberries, tomatoes, and peppers are some of the plants that require buzz pollination to release pollen. In buzz pollination, the worker bee wraps her legs around the flower and vibrates her wing muscles without moving her wings. This creates a “buzz” that is musically similar to the tone of a middle C. The vibration shakes the pollen-holding anther, releasing the flower’s pollen like a salt-shaker releasing salt.
Bumble bees rarely sting when foraging for food, but can and will sting repeatedly to protect the nest. People are often stung when unknowingly walking near or stepping onto a bumble bee nest. Bumble bees do not have barbed stings like honey bees do, and so can sting repeatedly.
About a dozen species of bumble bees live in Ohio. According to the Ohio Bee Atlas, a citizen science project on the iNaturalist platform (inaturalist.org), the following are the nine most commonly observed bumble bee species by citizen scientists in 2017 and 2018, from most to least commonly observed:
- Common Eastern bumble bee (Bombus impatiens)
- Brown-belted bumble bee (Bombus griseocollis)
- Two-spotted bumble bee (Bombus bimaculatus)
- Golden northern bumble bee (Bombus fervidus)
- Perplexing bumble bee (Bombus perplexus)
- Half-black bumble bee (Bombus vagans)
- Black-and-gold bumble bee (Bombus auricomus)
- American bumble bee (Bombus pensylvanicus)
- Lemon cuckoo bumble bee (Bombus citrinus)
Several species of Ohio bumble bees that used to be common are becoming much less so, such as golden northern bumble bee, black-and-gold bumble bee and the American bumble bee. The rusty-patched bumble bee (Bombus affinis) was listed as a federally endangered species in 2017 and has only rarely been spotted in Ohio in the last two decades.
Bumble bees face many of the same threats facing honey bees and other pollinators, including lack of flowers, decrease in nesting habitat, and poisoning from pesticides. Bumble bees are also impacted by diseases that only infect bumble bees, and are thought to be particularly vulnerable to changes in climate
To conserve bumble bees, gardeners and land managers of any scale can protect potential and actual nesting sites, provide flowers that bumble bees prefer, and decrease or eliminate pesticide use.
A few flowers bumble bees prefer:
Trees: black locust, cherry, crab apple, redbud, willow, redbud
Native perennials: aster, goldenrod, ironweed, monarda, purple coneflower
Weeds: birdsfoot trefoil, chickory, red clover, teasel, white clover
For more information:
Bumble Bee keys including Ohio: beespotter.org/topics/key/
Bumble Bees of the Eastern United States (free PDF guide) by Sheila Colla, Leif Richardson, and Paul Williams: pollinator.org/assets/generalFiles/BumbleBeeGuide2011.pdf
Ohio Bee Atlas: go.osu.edu/ohiobeeatlas
Bumble Bee Conservation, The Xerces Society: xerces.org/bumblebees/