The Western Bumble Bee is a medium sized (1-2 cm) bumble bee that has a band of yellow hair across the thorax (i.e. the middle part of the bee, between the head and the abdomen) at the base of the wings and almost always has a white-tipped abdomen. The Western Bumble Bee used to be one of the most common bumble bees found in western Canada (ranging from southern British Columbia, across southern Alberta and into Saskatchewan), but recent population declines due to habitat loss and fragmentation, pesticides, and competition with and diseases from agricultural bumble bees have made the species rare.
Bumble bees do not live in hives, instead most bumble bees make their nests underground, often using holes within decaying wood, openings in rotten logs, grassy mounds, or abandoned rodent burrows. Each spring, mated queens emerge from hibernation and set out to find nest sites to begin a new colony. Once the queen decides on a nest site, she lays eggs in the nest and goes out to forage for nectar and pollen. The life cycle of the Western Bumble Bee has four stages: egg, larva, pupa, and adult. After four days, the eggs hatch and the queen feeds the larva on pollen and nectar. After two weeks, the bumble bee larva spin cocoons and pupate. It takes two weeks for the pupae to develop and hatch into adults, and the whole process to get from egg to adult takes about five weeks; this timeline can vary with temperature and food supply. The first adult bumble bees to emerge from the colony are female worker bees and they take over the foraging duties from the queen, and are also now in charge of feeding the larva. Later in the summer, once the colony has reached its maximum for worker bees, it then begins producing male bees and potential new queens. These males and new queens do not stay in the colony and instead they leave and go mate with similar bees from other colonies. The new queens mate before going into hibernation for the winter, so that when they emerge the next spring, they don’t need to bother finding a male and can get started laying eggs. The male bees, worker bees, and original queen all die in the fall.
The Western Bumble Bee is a generalist forager, which means that it can eat the nectar and pollen from many different types of flowers and is not dependent on a specific plant species for its food. Since the queens emerge early in the spring, the Western Bumble Bee needs early blooming flowers, as well as continued blooms through the summer and into the fall to ensure it has enough food to feed the colony for the entire time it is active. In addition, bumble bees need options in terms of different types of flowers to ensure that they get all the nutrients required to feed the growing baby bees (i.e. larva).
Here are three things you can do that will help the Western Bumble Bee, as well as other native pollinators.
- Plant flowers – the two main things to remember are that bumble bees need flowers from early spring until fall and that they need a variety of different types of flowers. Whenever possible, it is always better to plant flowers that are native to where you live, rather than species that come from elsewhere. Check out pollinator guides to see what flowers are native to your area so you can make a list before going to the garden center.
- Build a bumble bee house. Although bumble bees usually nest underground, sometimes they will use a bumble bee house instead. Plans for a bumble bee house can be found here or here, depending on which style of house you’d like to make.
- Adopt a Western Bumble Bee. Your adoption will help Earth Rangers support Nature Conservancy Canada as they work to restore this important species throughout southern Saskatchewan.
Many thanks to Sarah Ludlow from the Saskatchewan Region’s Conservation Science Team at the Nature Conservancy of Canada for writing this article.