There is an old white pine stump by my house left from a tree cut down about 40 years ago. The bark has long since fallen off and wood is soft and weathered. Soon after the tree was cut long-horned beetles found the stump and laid eggs in the bark. These hatched into flattened white grubs that ate the inner bark and sapwood for two years before pupating and transforming into adult beetles. The grubs have hard powerful jaws to chew through the wood and in their quest for food they left many spacious tunnels with large openings to the outside. Now that the stump is no longer food for the grubs the empty tunnels are used as brood chambers by bees.
Many species of small bees are efficient pollinators of wild plants and cultivated plants. Some nest in underground tunnels but others nest in wood or hollow plant stems. Having a few old stumps nearby and leaving some large dry snags along field edges are good ways to provide nesting sites for wood-nesting and cavity-nesting bees. Bee species that will benefit include large carpenter bees (Xylocopa), mason bees (Osmia), and small carpenter bees (Ceratina). You can mimic stumps and snags by placing large logs upright into the soil. Use logs with a beetle grub tunnels or drill new holes for the bees to use. Logs and stumps with hollow interiors will also make good nesting sites for some bee species.
I’m not sure if the bumblebees even have active hives anymore. I doubt they do as there are almost no flowers left except for a these garden asters and a few tattered flowers elsewhere and that is not much for a colony to live on. Still, everyday when the temperatures get above 50 degrees the bumblebees are actively working their way across the masses of aster flowers gathering or maybe just eating one last meal of nectar and pollen. This might go on for another week but very soon even the daytime temperatures will be too cold for these worker bees and they will die. By then the new queens will have found safe hideouts in clumps of grass and leaves to wait out the winter. Perhaps this one is a new queen. Her wings are shiny not dull and ragged. Let’s hope the winter is good.
With the end of summer also comes the end of flowers and of the bumblebees that feed on their nectar and pollen. Bumblebees are colonial insects that live in small hives of fewer than a hundred individuals. There is a queen who lays eggs most of which are non-breeding females who tend to the needs of the larvae and collect food for the colony. Towards the end of summer male bees and fertile females are hatched. These will mate after which the males die.
Today there were many bumblebees feeding on the last of the late summer flowers. The goldenrods and most of the asters are done but there are huge patches of New England Aster (Aster novae–angliae) in full bloom planted around the house and these are covered by dozens of bumblebees all day long. I suppose all this activity is to gather food for the new queens and males if any are still in the larval state. It doesn’t seem that these bees are themselves queens as they are too small. Soon the new queens will have mated, the asters will die after a hard frost and with them the worker bees and the old queen. But the new queens will, it is hoped, find a safe shelter to wait out the winter under leaves and duff. When spring comes and the first willow flowers in the marshes and fens bloom the new bumblebee queens will awaken to start the cycle over again.