Bumble bee (Bombus species). Photo by Jim McCulloch.
Chances are when you think of “bees” you picture honey bees: black and yellow striped, living in a hive lorded over by a queen, collaborating to produce honeycombs, apt to sting. Honey bees have captured our collective imagination, but they are far from typical. Bees can actually be black, brown, or green; they can be as small as 1/8-inch long or longer than an inch; and the vast majority of North American bees are solitary creatures that nest in cavities or soil.
In fact honey bees, Apis melliflora, are relative newcomers to North America, brought here (like so many other immigrants) to support agriculture. And they represent just one of close to 20,000 identified bee species, 4,000 of which are native to North America. About 430 bee species have been identified in New York State; over 200 in New York City. In a four-year study of bees in New York City community gardens (see Resources, below), researchers identified 54 species. So if you look closely at your own garden or the green spaces around you, you are likely to spot a diversity of these busy buzzers.
The Great Pollinator Project
Looking at bees and flowers is the work of the Great Pollinator Project, a collaboration between the American Museum of Natural History’s Center for Biodiversity and Conservation and the New York City Department of Parks’s Greenbelt Native Plant Center. The program uses citizen scientists to track the activity of New York City’s native bees, with an eye toward conserving bee habitat and improving urban plant pollination.
Bees gather nectar, pollen, and sometimes floral oils or other aromatic compounds for sustenance and as food stores for their offspring. Most bees have a patch of stiff hairs under their abdomen or along their hind legs, called a scopa, into which they push grains of pollen to bring back to their nest. The pollen is held on the special branched hairs by an electrostatic charge that is created when the bee beats its wings. Pollination occurs as a bee moves from plant to plant, inadvertently distributing some of the pollen it’s collected to the fertile female parts of other flowers. Most flowering plants require an animal pollinator, and bees are recognized as being more efficient at the task than any other pollinating insect.
For the Great Pollinator Project, volunteer bee watchers are provided with a set of native plants that they then observe for a half hour at least every other week, identifying bees that visit as one of five types (honey bee, bumblebee, carpenter bee, green metallic bee, and “other”). Bee watchers record their observations on a data collection sheet and then submit them online. The study is helping to increase understanding of bee distribution while suggesting park management and home-gardening practices that can benefit native bees.
Besides native or nonnative origins, bees can be characterized by their social behavior, nesting preference, and floral specificity. Most bees will collect pollen from a wide variety of plants; however, some bees are more selective. For example, Melissodes species forage mainly on plants in the sunflower family (Asteraceae), specializing in asters, daisies, and sunflowers. (In fact, Melissodes are the primary pollinators of sunflower crops.)
Specialists, which are called oligolectic, and their preferred floral species often exhibit reciprocal adaptations: for example, some bees’ daily collecting activity is at the particular time of day when the plants release pollen; others have body features that match floral forms and facilitate nectar collecting. In the study of New York City community gardens, only four percent of the observed bees were oligolectic; the majority were polylectic.
Some bees don’t harvest their own food but instead steal that of other species. Cleptoparasitic bees lack pollen-collecting structures; they lay their eggs in the cells created by other bees, where, on hatching, the parasitic larvae eat the pollen stores and the host larvae. About three percent of the bees observed in New York City community gardens were parasitic.
Social bees nest together in colonies and distribute labor and reproductive functions. For example, a honey bee colony consists of a queen bee, who lays eggs; male drones, who mate with the queen; and female worker bees, daughters of the queen, who perform most of the tasks that maintain the colony. Worker bees collect nectar and pollen, then convert the nectar into food stores (honey) and the pollen into bee-bread to feed newly hatched larvae. They build wax cells to hold food stores and for the queen to deposit eggs in, and they protect the hive and care for the young brood. A typical honey bee hive contains one queen, a hundred drones, and 20,000 to 40,000 workers.
Honey bee colonies are perennial; the queen will hibernate over the winter and live for about three or four years. Worker bees live about three weeks, and drones usually die after mating or are driven from the hive during the winter. When a queen ages or a hive becomes overpopulated, the worker bees will raise a new queen bee. Honey bees are recognized as the most complex among social bees.
Native bumble bees, Bombus species, are also social, but their lifestyle is very different. Most bumble bee colonies are much smaller, usually numbering 50 to 200 individuals, and they prefer to nest in the ground. Bombus colonies are annual. A bumble bee queen will mate in the fall, then diapause over the winter, waking alone in the spring to find a nest site and lay the eggs that will mature to become her colony. The following fall, new queens and males will hatch. The new queens will leave the nest to mate and find sheltered spots for winter diapause, and the old queen, workers, and males will die.
In truth, these complex social systems are the exception to the rule among bees. The majority of native bee species, 85 percent, are solitary. In solitary bee species, every female is fertile; she typically inhabits a nest that she constructs herself and cares for her own young. Solitary bees do not produce large quantities of honey or wax, they are relatively docile, and most are immune to the parasites and diseases that are causing colony collapse disorder among honey bees.
Solitary bees are may still live near each other. They may aggregate their nests at favorable sites; they may be communal, meaning that they share a nest but each female tends to her own cells and brood; or they may be subsocial, which means that they associate but lack a fixed organization.
Solitary bees create nests in hollow reeds or pithy stems, natural or man-made cavities, or, most commonly, in tunnels they dig in the ground. They may create simple holes or extensive burrows or mounds. In urban environments, solitary bees face particular habitat challenges, including pollution and synthetic chemicals; fragmentation of green spaces; unnatural shade, moisture, and microclimates; and paved, compacted, or frequently disturbed soil.
One of the most surprising discoveries emerging from the community garden study was the prevalence of exotic species. More than a quarter of the individual bees observed were nonnative to North America. (In studies of exurban areas near New York City, only about two percent of individuals were nonnative.) Researchers surmised that the intensive development of the metropolitan area served to selectively exclude ground-nesting species. Exotic species may adversely affect native populations through competition for nest sites and floral resources, however, the degree to which this happens in urban gardens has not been determined.
“The decline of honey bees has gotten people really interested in what is going on with bees,” says Kevin Matteson, postdoctoral fellow at Fordham University and one of the coordinators of the Great Pollinator Project. “It highlights the problem of relying solely on one species, and why biodiversity is important. Having a suite of different species to provide pollination in the city gives us insurance.”
How to Help Native Bees
Bees are sometimes feared, but virtually all bee species are nonaggressive, and many do not sting at all. Humans are usually a greater danger to bees than vice versa! Here are some ways you can help support native bee populations.
Plant natives. Native plants coevolved with native bees and often offer the best nutrition and habitat. Group several plants of the same species in clusters, and provide a diversity of species in your garden. Those features (color, fragrance) that attract bees are often attractive to humans as well.
Avoid pesticides. Look to integrated methods to discourage pests, rather than chemicals that kill indiscriminately.
Offer nesting options. Logs, dead branches, and woodpiles provide natural habitat. You can also buy or build nesting blocks.
Reduce soil disturbance. Set aside at least one area of the garden where you will not cultivate soil, allowing bees a place to construct underground tunnels and nests.
Educate your neighbors. Teach your friends, students, or community gardeners about the importance of pollinators and native bees.
Participate in a bee conservation project. Register as a bee watcher for the Great Pollinator Project, or join one of many other projects.