Why does it take a chipmunk to get a nest of bumblebees going? At our September 15 tea party in the High Park Pollinator Garden I had a chance to show Pollinator Gardens project members Joanne Jenkins and Judy Whalen why.
Actually, a mouse will do just as well as a chipmunk. Many species of bumblebees nest in old rodent tunnels. Typically the mouse or chipmunk mother has left behind nesting materials (grass, bits of fur) in a deep, protected part of the tunnel. Her babies were kept warm in these cozy nests. That's what bumblebee queens are looking for: a safe, protected spot where bumblebee babies (say that 3 times quickly!) can be kept warm - around 32 degrees Centigrade or or 88 F.
Some species of bumblebees will nest in tufts of grass like the one shown above. The main thing seems to be good insulation. Some will nest aboveground in holes in wood or similar spots. Bumblebees can't cool their nests down as easily as honeybees. Honeybee colonies will have large numbers of bees fanning at the nest entrance on hot days; there just aren't as many bumblebees in a colony so being underground may be good protection against overheating.
You can make an artificial bumblebee nest early next spring. Just remember to get it out early enough - queens fly about when the first flowers come out, looking for a good site. Don't put it where it may get soggy, and avoid nearby ant nests. There are also designs for above-ground nests.
Why should we make artificial bumblebee nests? Many people tidy their yards up very thoroughly, rake garden beds, and generally remove sites where bees might nest. If this describes you, consider putting out a nest or three.
The bumblebee on the right came to early blooms in Amro Zayed's pollinator garden - thanks for the great picture, Amro! Like many bees, bumblebee populations have declined in the last few decades, and some species have gone extinct.
This ought to be a particular concern to all of us who love to grow and eat tomatoes, peppers, eggplants, blueberries, and cranberries. These and about 8% of the flowering plants in the world need "buzz pollination" to set seed and grow fruit properly. These plants hold their pollen tightly and only release it when a pollinator buzzes, and bumblebees buzz much more than honeybees. That's why bumblebees are used to pollinate greenhouse tomato crops. This was a considerable improvement on the "electric buzzers" previously used to pollinate greenhouse tomatoes.
Unfortunately, as often seems to happen, good intentions have led to problems. Bumblebees are now grown commercially and distributed to greenhouse growers. Unfortunately, commercial bees are often infected with various diseases, and can easily escape from greenhouses. York University researcher Sheila Colla has shown that wild bees near greenhouses are victims of "pathogen spillover".
All of which helps explain why I was so pleased on September 15 to see bumblebees apparently appearing from nowhere in the High Park lawn just 2 meters (six feet) from our pollinator garden. I strolled over and saw many workers flying into a chipmunk burrow with the pollen baskets on their legs full of yellow grains of pollen and emerging pollen-less for another foraging trip. I might not have noticed them if I hadn't been there a bit early setting up the tea table. I sat down with my dog to enjoy the view. Just where the garden bed bends, I saw many bumblebees flying.
The new queens will mate with drones from other colonies and then find themselves a safe place to spend the winter - not in their parental colony but often buried in soft earth or gravel.
You too can create an overwintering spot for queens. Just find a spot, ideally under the eaves of your house or garage, dig a small pit, and fill it with the lightest, loosest gravel you can come by. No need to clean out a coal furnace for half a century - if you can find "lava rock" of the kind sold for barbecues, that will do very well.