Would you like to hear your neighbors buzzing about how good your garden looks? There's an easy way to do that and help an important native pollinator at the same time.
Plant a bumblebee-friendly garden. You'll do yourself and bumblebees a favor.
Several once-common species of North American bumblebees are suffering significant range restriction and reduced abundance, according to surveys by the Xerces Society, an international nonprofit that advocates for invertebrates and their habitats.
Scientists don't have sufficient data to make a good determination about the status of most bumblebee species, said Robbin Thorp, a professor emeritus in the Department of Entomology and Nematology at the University of California at Davis. "Some species are in very serious decline," he said. "Some others are doing well and even expanding their ranges."
For example, most studies tend to focus on a particular species in a particular area like this research conducted by York University and published in the journal of Insect Conservation, which found that the American bumble bee is critically endangered in southern Ontario. That's just one species, but the factors at play are important for all bumble bees.
While the causes of decline aren't fully understood for the species with decreasing populations, the likely factors include loss or fragmentation of habitat, pesticide use, climate change, overgrazing, competition with honeybees, low genetic diversity and, perhaps most significant of all, the introduction of nonnative pathogens.
Why is understanding what might harm bumblebee populations important?
In North America, it is believed that 30% of food for human consumption originates from plants pollinated by bees. Bumblebees are pollinators of high-value crops such as blueberries, cranberries, zucchini and eggplant and are the exclusive pollinators of greenhouse-grown tomatoes and peppers, according to Xerces. Homeowners can help preserve bumblebee populations by planting gardens and patio pots with ornamentals and vegetables that attract bumblebees.
How to entice bees to your garden
"Gardening for bumblebees is similar to gardening for other bees and pollinators," said Steve Buchmann, an adjunct professor in Entomology and Ecology and Evolutionary Biology at the University of Arizona who specializes in insect/plant interactions and who has researched bees extensively. To entice bumblebees to visit your garden, "plant mints, Salvia, Monarda, plants in the sunflower family and clovers," he advised.
The Xerces Society has published an excellent resource to help gardeners across the country know which bumblebee species are active in their areas and what to plant to attract them. "Conserving Bumble Bees" includes several regional appendixes that feature line drawings of bumblebees common in each of major regions of the country and a list of plants native to those areas that will attract these colorful bees.
The drawings in the guide are of the females of each species. That's because females are more likely than males to be seen visiting flowers. The species guide isn't comprehensive — some bumblebee species have varieties with different coloration — but it's an excellent primer.
The Xerces Society is conducting a citizen science project called Bumble Bee Watch to find rare bumblebees that are imperiled or in population decline. If you'd like to participate and believe you have seen any of the imperiled species featured in Xerces' guides, join the watch or contact Xerces. (It would also be helpful to send them a photograph for verification purposes as the project explains.)
Sunflowers and other yellow flowers are good bets for bumblebees. (Photo: deedavee easyflow [CC BY-SA 2.0]/Flickr)
One appendix of the Xerces bumblebee guide features an expanded list of regions and includes plants that bumblebees like to visit. It features native plants in a variety of colors that are highly attractive to bumblebees and bloom throughout the bees' entire flight season. The list also includes flowering shrubs and small trees that could be used in any planting plan. Flowering trees and shrubs can be fantastic early-season resources for bumblebees and are often the only plants flowering in early spring.
Accompanying the native plant lists is a short list of garden plants that are available nationwide. Xerces recommends heirloom varieties or those that are not highly ornate.
It's also important to keep several things in mind as you plan a bumblebee garden, Buchmann advised. One is that "bee flowers are typically blue or yellow and bilaterally symmetric." The other is that "it is important to have blooms from early spring until late fall."
Remember your vegetable garden when creating a bee-friendly garden. Bumblebees are important pollinators of America's favorite backyard vegetable, the tomato.
How bumblebees pollinate
Tomato flowers need to be shaken to transfer pollen to produce fruit. Gardeners have tried a variety of ingenuous tricks to accomplish this task. The bumblebee does it naturally through a process called buzz pollination, which you can see in the video below.
A bumblebee hovering over a tomato flower can create a vibration roughly equivalent to 30 times the pull of Earth's gravity, according to Buchmann. Fighter pilots, he said, typically black out after about 30 seconds at 4 to 6 Gs. "Bumblebees can sort of turn themselves into living tuning forks to sonicate pollen out of flowers," he added. Other vegetables and fruits that benefit from buzz pollination include blueberry, cranberry, peppers, eggplant and kiwi.
Bumblebees pollinate differently than honeybees in other ways. "Honeybees have a 6-millimeter long tongue," Buchmann said. "They can't reach into deep nectar tubes. While some bumblebee species, have short/mid length tongues, others are long-tongued species that can reach into the flowers of clovers and other blossoms."
Inside the bumblebee colony
Bumblebee colonies are annual colonies, he pointed out. The colony lives for less than one year.
Here's how Buchmann said the colony lifecycle works. An overwintering queen bee starts the colony in the early spring, the dates of which vary across the country. In the late summer or early fall, the colonies produce virgin queens and males. These mate, the males and the colony die except for some of the mated queens. Surviving mated queens overwinter until the following spring by essentially hibernating in crevices, old mouse nests, soil banks, or similar places.
"Some people have tried to bury nest boxes for these bees, but it's tricky," said Buchmann. "I wouldn't recommend it for home gardeners." (In the video above, one gardener created an environment for bumblebees, including a next box, which allows you to see what a colony actually looks like.)
A better way to encourage bumblebees to nest or overwinter in or near your garden is to create natural nesting habitat, said Nancy Adamson, pollinator conservation specialist for the Xerces Society and the USDA Natural Resources Conservation Service. "Good habitat includes un-mown native bunch grasses, brush piles, and dead trees," she said. Echoing Buchmann, she said that any place a mouse might find appealing would be attractive to bumblebees.
Leaving some areas intentionally messy also enhances habitat for many birds and other wildlife, suggested Adamson. "Adding a sign so that visitors know these "unkept" areas are intentional helps start a conversation about bees and their needs," she said. "Other indications that the area is clearly cared for include a mowed edge, fencing, or pathways. Signs can be permanent (from organizations supporting wildlife habitat or pesticide-free zones) or laminated homemade signs that could change seasonally."
"Good habitat is also protected from pesticides," she added as a final bit of advice. "Even organic pesticides may harm bees."
Plant and protect habitat, enjoy your "buzzy" garden, and share the bounty of flowers and vegetables with family and friends!
To learn more about bumblebees, Buchmann recommends "Bumble Bees of North America: An Identification Guide." It's the first comprehensive guide written about North American bumblebees in more than a century; Robbin Thorp is one of the authors.
Editor's note: This story has been updated with new information since it was published in July 2014.