The Xerces Society, a nonprofit conservation organization, is a leader in the effort to conserve North America’s native pollinators. Founded in 1971, the society protects insects and other invertebrates through advocacy, education, policy development and applied research projects aimed at protecting and managing critical habitat. Attracting Native Pollinators (Storey Publishing, 2011), by The Xerces Society, is a complete action plan and information guide for protecting bees, wasps, butterflies, moths, flies and some beetles by providing flowering habitat and nesting sites.The following excerpt comes from Part 3: Bees of North America.
Bombus: Bumble Bees
Bumble Bees are among the most easily recognized and best-loved bees. There are nearly 50 species in North America, found primarily in temperate areas and ranging as far north as there is land.
Robust and very hairy, moderate to large bees, 0.4 to 0.9 inches (10–23 mm) long. They have yellow, black, white, brown, or orange bands by which different species can be distinguished, although there can be variation in color pattern even within a species. Bombus females carry pollen moistened with nectar in stiff hair baskets (corbiculae) on their hind legs.
Similar Types of Bees
Few bees are large enough to be confused with bumble bees. Large carpenter bees (Xylocopa) are generally not as hairy nor as brightly colored. Centris mining bees have distinctive, very large, hairy scopae on their rear legs. Digger bees (Anthophora) usually are not as brightly colored; a few species that mimic bumble bees may look like smaller bumble bee workers, although possessing scopae (an area of long, dense hairs on the hind leg) rather than the bumble bee’s corbiculae (an open area surrounded by long, incurving hairs). In addition, several syrphid flies are excellent bumble bee mimics.
Bumble bees are among the first bees to emerge in the spring and the last to disappear in the fall. They visit a succession of flowers from a wide variety of plants throughout the foraging season, from early-flowering willows to late-summer blooms such as goldenrod. Many species have long tongues that enable them to access nectar from deep flowers such as larkspur and penstemon. Bombus are important pollinators of crops as diverse as tomatoes, watermelons, and blueberries.
Bombus nest socially in annual colonies. At the end of summer most bumble bees die, leaving only a few mated queens to hibernate. In spring, the queens emerge, each founding a new colony as a solitary bee. The queen rears her initial brood; once those workers are ready to take over foraging, she remains in the nest to lay eggs.
Bombus nests consist of an irregular cluster of ball-like, wax brood cells in a small cavity such as an abandoned rodent burrow or under a grass tussock. The cells are unique among all bees because they may contain multiple offspring and are enlarged as the larvae develop. Provisioning of the cells is progressive, meaning that additional provisions are added as required. Bumble bees store small quantities of nectar, enough to supply the colony for only a couple of days.
Bumble bees in the subgenus Psithyrus are social parasites of other bumble bees. A Psithyrus female will enter an established nest and then usurp the host queen, either instantly by killing her or gradually by living alongside her. The Psithyrus queen is not always successful — she may be driven away or killed by the current occupants. Once established in the nest, she will lay her own eggs that the workers will tend. Psithyrus look similar to other bumble bees but lack pollen-gathering structures because they do not forage.
There has been an abrupt and steep decline in several bumble bee species, particularly Bombus occidentalis, B. affinis, B. terricola, and B. franklini. Recent research has found that the declining species have higher pathogen loads and reduced genetic diversity. In the 1990s, North American bumble bees were taken to Europe for breeding for the greenhouse tomato industry. It has been hypothesized that the bees contracted diseases in Europe that they carried back when they were subsequently reimported; these spread to wild populations.
Did You Know?
Bumble bees can buzz-pollinate. Some flowers such as tomatoes need to be vibrated to release the pollen (at roughly the frequency of a middle C musical note). Bumble bees do this by grabbing onto the flower and then vibrating their flight muscles without flapping their wings. There is an audible buzz as they do this, hence the name.
To learn more about bumble bees and other types of native pollinators, read How to Attract Native Bees to Your Organic Garden.
“Bee” an expert! Identify more types of bees from Attracting Native Pollinators
Regional Plant Lists for Native Pollinator Gardens
The following charts list plant species that are native to their respective regions and commercially available from nurseries, specialty seed producers, and local native plant societies. The plants listed here tolerate a wide range of soil and light conditions. They are listed by season, to make it easier to design a garden that provides forage in spring, summer, and fall. If particular species are difficult to find in your area, look for closely related ones.
Northeastern United States and Eastern Canada
Southeastern United States
Midwestern United States
Great Plains and Prairie Provinces
U.S. and Canadian Rocky Mountain Region
California and the Southwest
Pacific Northwest and British Columbia
This excerpt has been reprinted with permission from Attracting Native Pollinators: Protecting North America’s Bees and Butterflies by The Xerces Society, published by Storey Publishing, 2011.