I’VE been watching the bumblebees flying around the kitchen porch of our old farmhouse in Maryland, and wondering if they have a nest nearby, maybe under the eaves. They like shady spots, protected from the wind and the rain. There are probably some mason bees, too, holed up in the old boards of the barn, or in holes drilled by wood beetles in the trunks of dead trees.
The bumblebee and other native wild bees are all the more important in the garden now that the population of honeybees is in such decline — down to 2.4 million colonies last year from 5.5 million in 1945, according to the Department of Agriculture, due mainly, scientists say, to mites infesting the hives and, lately, to a mysterious epidemic called colony collapse disorder.
Native bees pollinate everything from pear and cherry trees to blueberries, tomatoes and eggplant. They are also fascinating to watch.
So the next time a bumblebee buzzes around your head, don’t swat at it. Follow it around. You might see it mating, or gathering nectar and pollen and flying off to its nest.
There are more than 4,000 species of native bees, according to “The Status of Pollinators in North America,” a 2007 report by the National Research Council in Washington.
Their total numbers are difficult to estimate because native bees are “hard to identify — they’re small, they fly under people’s radar,” said Scott Black, an entomologist and the executive director of the Xerces Society, an organization that studies insects.
But native bees are on the decline too and we need to encourage them, now that there are fewer honeybees. (The society has compared field studies from the 1950s through the 1970s with more recent studies, he said, and found “drastic decline” in at least three species of bumblebees: the Western bumblebee, the rusty-patched bumblebee and the yellow-banded bumblebee.)
The European honeybee, Apis mellifera, was brought here by the colonists in the early 1600s to make honey, said Tristram Seidler, the staff ecologist for the New England Wild Flower Society. “Its pollination service was only recognized later on,” he said.
Until then, from the time the first flowering plant was pollinated by a bee 120 million years ago, native bees had been doing the job just fine. In fact, Mr. Seidler said, they are at least 10 times more efficient than honeybees.
“They visit more plants per hour, at a fast speed, and make pollen more available,” he said.
Native bees fly farther between flowers, thus doing a better job at cross-pollinating than do honeybees.
And honeybees are at a disadvantage when it comes to certain flowers, like the blueberry. “Its petals are joined, with a very small opening, so the bee can’t even force himself inside,” Mr. Seidler said. “That’s why buzz pollination” — the bumblebee’s specialty — “is more effective.”
Buzz pollination is a process that sounds very nice for both flower and bee: Bumblebees and some other native bees “use their flight muscles to vibrate the flower until the pollen is shaken loose,” Mr. Seidler said. Like honeybees, they use their middle pair of legs to gather the pollen into pollen sacks. “You can see these on bees when they’re flying by.”
Sometimes they sit on the flower and vibrate; sometimes they hang upside down and do their thing. And when they fly off to other flowers, some of that pollen just naturally falls off and pollinates the plants.
Mason bees don’t have pollen sacks. “They have rows of stiff hairs on their lower abdomens,” Mr. Seidler said. “They use their legs to pack the pollen into those hairs, so that when they’re crawling around on other flowers, the sticky stigmas will get the pollen.”
That makes them better pollinators than honeybees, he said, because they are small and can really get down into those flowers.
Honeybees, however, build large colonies of 20,000 to 100,000 bees, so they have the numbers to pollinate huge commercial orchards or fields of tomatoes or strawberries. So growers have long rented them from commercial beekeepers, who truck in their hives, much like migrant workers, to pollinate the flowers when they open. When the job is done, they haul them out again, and the growers can spray the crops without harming the bees, which are sensitive to pesticides.
But now growers have an economic incentive to reduce their pesticide use — to help encourage the native bees in their area, which are not, of course, trucked in and out of their habitat.
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