We found a vibrating fuzzy mass in our croquet set bag this past weekend. A few bumblebees flew out of the mass so we were sure that it was a bumblebee nest. Earlier this spring we had plans to build a nesting site for bumblebees from an overturned flower pot, but other things took priority and we never did. So we were fortunate to come upon this little home.
The particular species of bumblebee we found (there are many) is Bombus impatiens, which is the most common bumblebee in the eastern United States. The queen is responsible for finding a suitable nesting site in the early spring, which could be an abandoned mouse nest, or another type of cavity. She secretes enough wax to create a honey pot and she regurgitates nectar into the pot, then goes off in search of pollen to store for rainy days when she will not be able to forage. After eating some of the pollen, her ovaries are stimulated to produce eggs and she will lay anywhere from four to sixteen eggs on the ball of pollen she has stored, which she then covers with wax. The queen will actually sit on her eggs like a bird and while she is keeping them warm, she stays fed on the honey in her honey pot. All the fertilized eggs will develop into workers (females) and later in the season, she will lay unfertilized eggs that will become males, and then fertilized ones that will become queens. For an egg to become a queen, the larva must be fed more than the other larvae.
As larvae, the bumblebees have no eyes or legs, and they spend about two weeks in this way. All they do is eat. They have a “blind gut”, meaning that they do not excrete any waste, until they reach the pupal stage. It takes about 4-5 weeks for the process of transforming from egg to adult to occur.
Workers live for about 4 weeks and they forage for most of that time. Males emerge at the end of the season, just before new queens. Mating occurs and the males die. The new queens spend their winter in hibernation after filling their honey stomachs. They are smart enough to find a place that won’t be prematurely warmed by the early spring sun, and therefore they usually don’t come out of hibernation early.
Bumblebees are extremely efficient pollinators, especially for blueberries, cranberries, alfalfa, and clover. They can fly in cooler temperatures than honey bees can (41 degrees versus 50 degrees).
lifecycle diagram courtesy of the wonderful Bumblebee.org (http://www.bumblebee.org/lifecycle.htm)