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People are now realizing the importance of, and understanding the diversity of bees as pollinators. As with all insects and arachnids, we advocate understanding the biology of a species and the use of integrated pest management to reduce risk. Scouting—the act of purposely looking for pest nests and pest activity—can reduce problems later in the year when the colony is well-established. Because bumble bee nests are hard to find, it makes sense to scout for stinging insect activity throughout the season. If you discover an active nest, don’t try to treat or seal bee or wasps inside a cavity or void, or treat with a pesticide.
Many bees and wasps are low-risk: mud daubers, potter wasps, cicada killers and various ground bees are rarely noticed until peak nest activity in late summer. Bumble bees are also low risk even though they are social bees, living in a colony. Adult bumble bees feed on flower nectar and pollen. Because of this, they don’t present a problem around human food or garbage. However, some bees may present a sting risk in flower gardens or in lawns where they visit clover blossoms. Avoid walking barefoot in such situations.
Unlike honeybees, bumble bees can sting repeatedly like wasps. Because of the discomfort and the risk of an allergic reaction, don’t wait until you witness a sting incident to know what to do.
Depending on the species, the various species of bumble bees can be up to one inch long (26 mm). Their thick bodies are often black with orange or yellow markings, and densely covered with hair. There are about fifty species in the US with similar traits.
Bumble bees build colonies of 50-400 in the ground—abandoned animal burrows, soft soil or organic matter like hay bales—or occasionally in structural cavities. Like wasps, their queens are the only ones to survive over the winter, and then go on to start up a new colony.
Bumble bees are a small to moderate sting risk to humans. Stings can occur when a foraging bee is in the wrong place. They are docile when alone, and do not sting unless they perceive danger to themselves or the hive. A multi-bee sting event is most likely to occur when the colony is disturbed by human or animal activity including the use of a mower or weed trimmer.
To reduce risk, avoid wearing perfumes, fragrant or flowery lotions, shampoos, conditioners and soaps. Avoid swatting at bees and wasps, or squashing them. Gently blow off, or brush off a wasp or bee that has settled on you. Avoid walking barefoot in lawns with clover or other flowering weeds. Scoop live bees and wasps out of swimming pools and place them away from busy areas. If you are concerned about a wasp or bee nest, consult a professional pest management company or beekeeper.
To feed the brood, adults forage for pollen and nectar flowers of fruit trees and shrubs, vegetables and ornamental plants. It is common to see bees on flowers on a sunny day. Having bumble bees around the yard and garden is a good sign of a healthy environment.
If you find a large nest, block off access to it for people and animals. If the risk of stings can’t be ignored, call your local cooperative extension for a list of experienced pest control experts.
Here’s a timeline for best management against wasp and hornet problems:
Early spring through summer:
Monitor buildings and grounds for stinging insect activity on warm sunny days; try to do this every other week. Pay close attention to the foundation of the building and the eaves of the roof. Watch for foraging workers and where their travels take them. This helps you discover nests or hive locations.
Late summer through fall:
Continue to monitor buildings and grounds. If you find nests or hives you can keep isolated from people and pets, leave them be. With wasps, remember that once the brood is raised, adults will leave the nest. Minimize food and food trash when possible in outdoor seating areas. Consult an expert if you find an active colony that poses a stinging risk to people and pets. Note where you find nests so you can make the sites unavailable for the following season, as bumble bee queens may return to the same area.
Plan a prevention strategy for the following season. Raise awareness among your family and neighbors or building staff about how using IPM can reduce stinging insect risks for the following season. For all wasps and hornets, seal holes in wall voids and roof eaves in late fall once activity has stopped, and fix flashing in eaves where wasps (and insects) can enter buildings.
Find and fill areas in soft soil where rotted wood or old animal burrows can accommodate ground nests. Rotate compost piles before or in early spring. Always have an action plan in place to care for people and animals who have been stung.
For more information on bumble bees, see Bumble Bees – Pollinators that Sting.