Bumblebees: hidden treasures of your gardens and fields
Photo: Elaine Evans
Figure 2. A view inside a bumblebee nest showing the queen surrounded by workers all atop the wax structure of the nest. Open wax pots contain nectar and pollen. Wax covered clumps contain immature bumblebees. The structure is much less organized than the perfect symmetry of honeycomb created by honey bees.
Bumblebees are familiar to most people as the big, cute, fuzzy bees they see on their garden flowers. While many people appreciate their good looks, few people are aware of these bees' good deeds. Bumblebees are very effective pollinators of many fruits and vegetables, including tomatoes, raspberries, cranberries, peppers, squash, and blueberries, as well as many native wildflowers. Good pollination not only increases production of fruits but also increases the size and quality of these fruits.
Bumblebees, as well as all other bees, have evolved alongside flowering plants and have developed interdependent relationships with many of these plants. Much of our food is reliant on bees for pollination. Until relatively recently, these pollination services were taken for granted. As long as crops were producing the needed fruits and seeds, there was no need to be concerned about pollination. As crops began to occupy more space and wild lands disappeared, wild pollinators were no longer sufficient in numbers to pollinate all the crops.
Who's the better bee?
Although there are over 20,000 species of bees in the world, one bee has dominated the roster of managed pollinators. That bee is the honey bee. We are very lucky to have a bee that is as well adapted for use as a managed pollinator as is the honey bee. Honey bees forage on a wide variety of crops, have large colonies with tens of thousands of bees, and, most conveniently, they adapt well to living in boxes that can be easily moved from field to field. On an individual bee to bee basis, bumblebees are more efficient pollinators than honey bees for most crops. However, honey bees are often considered to be more effective overall due to their large colony sizes. Honey bee colonies have 10,000 to 30,000 bees per colony, whereas bumblebee colonies typically have 50 to 500 bees per colony. While an individual honey bee may not transport as much pollen as an individual bumblebee, a honey bee colony can make up for their inefficiency with sheer numbers.
Recent alarm over Colony Collapse Disorder has brought concern about pollination to the world's attention. Over the past fifty years, honey bee keepers have faced an increasing barrage of challenges including pesticides, pests, and diseases, all while adapting to increased demand for pollination services. Part of the reason why honey bee populations have been so afflicted by problems with pests and diseases is that honey bees are transported long distances across the country with many colonies in close quarters to pollinate different crops. When transporting bees, the diseases and pests are transported along with them. This is part of the reason why these problems can spread so quickly through honey bee populations. Similar problems may arise for bumblebees if they are transported across the country for pollination. These problems can be deterred by using locally raised bumblebees.
Honey bees have many different disease and pest problems, including parasitic mites, viruses, microsporidians, and fungi. While most of these are specific to honey bees, this does not mean that bumblebees don't have their own array of problems. A similar slew of parasitic mites, viruses, microsporidians, and fungi affect bumblebees. However, in most cases, bumblebee pests, parasites, and diseases do not affect honey bees and honey bee pests, parasites, and diseases do not affect bumblebees. The causes and extent of damage from Colony Collapse Disorder are still being assessed, but one clear message is that we need to develop the use of pollinators other than honey bees. We need to develop a supply of supplemental and alternative pollinators.
Bumblebees know how to sip it and shake it
Bumblebees are an excellent alternative to honey bees or a supplemental source for pollination of many crops. There are several attributes of bumblebees that promote their use as pollinators. Some bumblebees have long tongues. These long tongues give bumblebees an advantage over short-tongued bees like the honey bee when foraging on flowers with long tubes, such as red clover. Bumblebees have been shown to fly in cooler temperatures and lower light levels than many other bees, extending their work day and improving pollination of crops facing inclement weather. Bumblebees perform a behavior called “buzz pollination.” In buzz pollination, the bee grabs the pollen producing structure of the flower in her jaws and vibrates her wings. This shakes pollen out of the flower that would otherwise remain trapped within the flower. Some plants, most notably tomatoes, require buzz pollination for effective fruit set. Bumblebees also adapt very well to the greenhouse environment, making them a potent pollinating force for the greenhouse industry.
Be a bumblebee booster
There are two avenues you can take to promote bumblebees. The first is to preserve or restore wild areas that provide food and shelter for bumblebees. Bumblebee nests are formed either in clumps of grass above ground or in holes below the ground, typically in old mouse nests. You can increase nesting site potential for bumblebees by leaving some areas of tall un-mown grass and untilled areas. Since bumblebees get all their nutrients from flowers, it is possible to simultaneously beautify your landscape and help your local bumblebees. Plant flowers, trees, and shrubs that will provide a constant source of blooms. Early spring flowers are particularly important as this is when bumblebee colonies are getting their fledgling starts. Bees tend to be particularly attracted to flowers that are blue, purple, and yellow. These flowers will be most effective in attracting bees if they are planted in single species clumps that are four feet or more in diameter.
Minnesota bumblebee flowers
It is best to plant your garden with flowers that supply a continuous supply of fresh blooms. Avoid horticultural varieties that have been bred for show. These may not have adequate supplies of nectar or pollen for bees. Native flowers are an excellent choice as they are well adapted to our local environment and our local bumblebees. This is a small sampling of possible flowers.
|Spring||Rhododendrons and Azaleas*||Rhododendron spp.|
|Early summer||Virginia waterleaf||Hydrophyllum virginiana|
|Mid-summer||Anise hyssop||Agastache foeniculum|
|Bee balm||Monarda fistulosa|
|Purple prairie clover||Dalea purpurea|
|Joe-pye weed||Eupatorium maculatum|
|Wild mint||Menthe arvensis|
*While these flowers are not native to Minnesota, they are good suppliers of pollen nectar for bees.
The other avenue to promote bumblebees is to raise your own bumblebees. In the wild, bumblebee colonies are started anew each spring by queens who mated the previous fall and hibernated through the winter. In early spring, these queen bumblebees can be found foraging at flowers and searching for nesting areas. By capturing these queens and providing them with a home, you can raise your own bumblebee colonies that can be used to pollinate your garden, your field crops, or your greenhouse plants. See Befriending Bumblebees: A practical guide to raising local bumblebees for details on raising your own bumblebee colonies. Raising bumblebees is an excellent project for youth groups, garden clubs, or small scale farmers.
Keep ‘em buzzing
It is a joy to see bumblebees diligently buzzing from flower to flower in your garden, intent on their mission to gather nectar and pollen to feed their family back at home in their nest. Beautifying your landscape with native flowers is a great way to help these bees. By raising your own bumblebees, you will gain a greater understanding of what life is like for these important creatures. Not only that, but you will be rewarded with bigger, better tasting raspberries, tomatoes, blueberries, apples, squash, and strawberries.
Elaine Evans received her M.S. in entomology from the University of Minnesota. She is currently working on a project for the Xerces Society for Insect Conservation researching recent declines of bumble bees in North America.
Published in Yard and Garden News, September 1, 2007