Searching the forest for the bees

— Every week this spring, Pat Groller drove to remote Dorchester Pond and traipsed through the forest, bucket in hand, to check her traps. Her quarry: The mysterious bees that keep wildflowers blooming here year after year.

"It's a trek, but I've enjoyed it," Groller said recently after she'd collected the contents of nine colored plastic cups staked out on the ground. She logs more than 90 miles round-trip from her home in Preston to run traps at three wooded sites on the Eastern Shore.

The 73-year-old grandmother is a volunteer in a small army of citizen scientists taking stock of wild bees in the forests. Organized by the U.S. Geological Survey, the first-of-its kind count is sampling more than 100 wooded sites across Maryland, Delaware, the District of Columbia and Virginia.

"We're interested in what kind of woods the bees are occupying," said Sam Droege, head of the geological survey's bee inventory and monitoring laboratory in Beltsville. The survey is opening a window on a "secret world," as one ecologist put it, of an intricate interaction between forest plants and a dizzying array of pollinating insects.

Scientists are also concerned to find out how wild bees are faring, Droege said, in light of the troubling declines documented in cultivated honey bee populations nationwide.

Researchers reported Thursday that beekeepers nationwide have lost one in three honey bee colonies since last spring, while Maryland's chief apiary inspector said honey bee colony losses among the state's mostly part-time beekeepers approached 50 percent.

A national survey of beekeepers found that they lost one in five honey bee colonies over the winter, fewer than the winter before. But they reported seeing substantial die-off in summer as well, pushing their year-round losses to more than a third.

While many beekeepers and some researchers have linked the die-off to pesticide exposures, the team that did the survey says no single culprit appears responsible for all the honey bee deaths. Those beekeepers who treated their hives for a common but lethal parasite, varroa mite, suffered fewer losses, said Dennis vanEngelsdorp, a University of Maryland entomologist who led the survey.

Domesticated bees are important economically, producing honey and pollinating agricultural crops; wild bees perform a vital role too in maintaining the natural vegetation that we sometimes take for granted.

Scientists have documented declines of wild bumblebees, but Droege said it's not clear that other native bees are in any particular trouble.

"We really don't have an issue that's some kind of mysterious broad-scale decline,'' he said.

Native bees seem unaffected by parasitic mites and other ills plaguing honey bees, which are not native, Droege said.

Droege, 55, and his colleagues have been sampling the wild population for years. They've logged more than 413 species in Maryland, including some honey bees and other non-native bees that were brought here at one time to serve as pollinators and have become "naturalized."

"We're regularly picking up new species of bees," he said, "not because they become new, but because of lack of feet on the ground or eyes in the sky."

The biggest and most familiar of the natives are bumblebees, but many are much smaller, and some downright tiny, such as sweat bees.

Scientists have focused mostly on studying wild bees in meadows and other open areas, but Droege said relatively little is known about the forest denizens.

"We've always known that native bees are in forests," he explained, "and that a lot of them are dependent on some of these forest blooming plants."

Unlike honey bees, which congregate in hives, most of the forest bees are loners that spend the bulk of their lives in the ground. They emerge for just a few weeks in early spring to pollinate flowering plants, shrubs and trees before the forest leafs out and shades the understory from the sun.

Many are "specialists," Droege said, focusing on a particular type of plant or flower.

For example, he said, there's a bee that specializes in collecting nectar and pollen from spring beauty, a ground-hugging pink or white wildflower that's one of the earliest harbingers of spring. One can't exist without the other, he said. In fact, many flowers have features that attract particular pollinators, while discouraging or excluding others.