|While the southern range of bumble bees is moving north, the northern range seems to be stationary. English photo|
By Sue Smith-Heavenrich
As the planet warms, many animals – and even plant populations – are migrating to cooler areas. Some expand their ranges northward; others move upslope, to higher elevations. But not bumble bees.
A team of Canadian, U.K. and U.S. scientists discovered this when they assembled a database of approximately 423,000 georeferenced observations for 67 bumble bee species from Europe and North America. They divided the records into different periods – 1975 to 1986, 1987 to 1998 and 1999 to 2010 – and compared them to a baseline period from 1901 to 1974. For each kind of bumble bee, they mapped its northern and southern range limits, its “thermal range” (the warmest and coolest temperatures it occupied) and the mean elevation of the population.
Agricultural researchers have already documented northward range expansion for butterflies and for mountain pine beetles and other pests, so the bumble bee scientists expected to see something similar. Instead they found that while the southern limits of the bumble bee territories retreated – 300 km (186.4 mi) – the northern edge did not change. This held for bumble bees in both the U.K. and North America. The scientists also discovered the bees had moved to higher elevations – 300 meters (984 feet) up mountain slopes.
The researchers built statistical models to test whether the range shifts might be due to land use (agriculture or urban development) and pesticide exposure (in particular, neonicotinoids). Those models indicated that a warming climate is responsible for squeezing the bees between a rock and a hot place.
A recent study at North Carolina State University reinforces those findings. There, researchers tested the heat tolerance of 15 species of native bees in the lab. To mimic climate change they observed bee populations in urban “heat islands” – areas where the abundance of cement and steel and the lack of greenery contributed to higher temperatures than the surrounding environments. Over two years the team followed bee populations at 18 locations in Wake County. When they compared bee populations in warmer areas to those at cooler sites, they found that bees with low heat tolerance in the lab, including bumble bees and sweat bees, tended to be less abundant in heat islands.
Why aren’t the bees expanding their range to the north? The difference in daylight or perhaps in food resources could be responsible, as could the small size of bumble bee colonies, usually 50 to 100 individuals, and their slow growth. Jeremy T. Kerr, biology professor at the University of Ottawa, observed that the buff-tailed bumble bee (Bombus terrestris) is an exception: It has expanded its range north and is, he says in Science, the “dandelion of the bumble bee world.”
Saving Maine’s Natives
Maine has 17 native bumble bee species, but according to Frank Drummond, two of those, the rusty patched bumble bee (B. affinis) and yellow-banded bumble bee (B. terricola), are almost extinct in southern Maine and are rare in the northern part of the state. Drummond would know: He’s a biology professor at the University of Maine and has been studying insects, particularly Maine’s native bees, for many years.
In 1989, when Drummond started collecting bees, the rusty patched bumble bee made up 20 percent of the state’s bumble bee population. By 1990 it was hard to find, and in December 2016 it was listed as an endangered species.
Even the common eastern bumble bee (B. impatiens) is getting hard to find and now makes up only 20 percent of the total bee population Drummond sees. Bumble bees are important to Maine farmers because they’re active at cooler temperatures, even on cloudy and foggy days. Honeybees are less active under those conditions. Bumble bees also pollinate plants using a rapid vibration called “buzz pollination,” which is more efficient than honeybees’ method, and they visit more flowers than honeybees over the same period of time.
Without bumble bees, many of Maine’s crops would have lower yields, so Drummond collaborated with colleagues to produce pamphlets and fact sheets encouraging gardeners and homeowners to plant native species that provide pollen for native bees.
Be a Bumble Bee Hero
The good news is that people can help native bumble bees. The first step is to reduce our carbon footprint. Beyond that are specific actions to help save our native bumble bees.
Learn about bumble bees. Protecting them starts with knowing as much as you can about their ecology, why they’re important, and ongoing conservation efforts. Then share what you learn. A lot of people are afraid bees (and other insects), so tell your family and friends how important bumble bees are. Encourage them to watch bumble bees and even take photos.
Create habitat! Become a steward of bumble bee habitat in your backyard, school, community parks and rooftop gardens. Converting lawns to native plants would create millions of acres of bumble bee habitat. Some states encourage solar farms to grow pollinator plants between rows of solar panels.
Feed the bees. Bumble bees and other native bees need pollen and nectar all summer, so when planning gardens or planting trees, make sure to plant some that bloom early as well as some that bloom into fall. Choose native plants when possible. Early bloomers include maples, apples, cherries, plums, willows, violets, crocuses, raspberries, black berries and dandelions. For midseason flowering, plant roses, rhododendrons, milkweed, purple coneflower, oregano, mint, marigold (single-flowered), borage, sunflowers, clover and field thistles. Late season flowers include asters, phlox, coneflowers, goldenrod and cosmos.
Find out more about pollinator plants suitable for Maine and the Northeast at the Xerces Society (xerces.org/pollinators-northeast-region/), the Wild Seed Project (wildseedproject.net/) and NRCS (https://www.nrcs.usda.gov/Internet/FSE_DOCUMENTS/nrcs142p2_010204.pdf).
Support local and organic agriculture. Agricultural areas provide both food and danger to native bees. Vegetable and fruit plants provide pollen-filled blossoms, but pesticides harm bumble bee colonies. Encourage local farmers to reduce or eliminate spraying.
Help scientists determine where bumble bees are abundant and where their populations are declining. Become a citizen scientist and collect data in your area by joining a project such as one of those below.
- Bee Hunt – Collect data by photographing bees at study sites and other activities. (discoverlife.org/bee/)
- Great Sunflower Project – Count the number and types of pollinators visiting plants (especially sunflowers) in yards, gardens, schools and parks (greatsunflower.org/).
- Bumble Bee Watch – Upload photos of bumble bees to a virtual bumble bee collection. Photos also help researchers determine the status and conservation needs of bumble bees and locate rare or endangered populations of bumble bees. (bumblebeewatch.org/)
- Maine Bumble Bee Atlas – Trained citizen scientists help document the diversity, distribution and abundance of bumble bees in Maine. (mainebumblebeeatlas.umf.maine.edu/)
Carpenter Bee or Bumble Bee?
Bumble bees look like furry flying teddy bears. Another large black-and-yellow bee looks a lot like a bumble bee: carpenter bees. Both are hairy, large and relatively slow-flying. But look closer. A carpenter bee’s abdomen is bare and shiny black. Bumble bees have hairy abdomens, with some yellow or orange markings. Also, carpenter bees tunnel into wood to nest, while bumble bees nest in the ground.
Need help identifying bumble bees? The Xerces Society provides a downloadable field guide to eastern bumble bees (xerces.org/bumble-bee-identification/) as does the USDA Forest Service (www.fs.fed.us/wildflowers/pollinators/documents/BumbleBeeGuideEast2011.pdf), and the Maine Bumble Bee Atlas project lists bumblebees found in Maine, with links to photos. (mainebumblebeeatlas.umf.maine.edu/me-bumble-bees/maine-species-list/)
Crops Pollinated by Bumble Bees
Scarlet runner beans