A bulldozer rumbled atop a massive construction-rubble landfill nearby as Sam Droege and Thom Wilson went bee-hunting beneath high-voltage power lines slicing across northeastern Baltimore.
Every few steps he took, Droege — a wildlife biologist with the U.S. Geological Survey — swiped the long-handled net he carried at the winged insects he spied on colorful little wildflowers popping up amid the weeds and trash.
He examined one of his catches: "There's a little Ceratina, a small carpenter bee." And, farther on: "Here's a little bee, on this chicory."
Wilson, a self-taught naturalist from nearby Armistead Gardens, kept pace, rattling off the scientific and common names of the bees and the blossoming plants attracting their attention: milkweed, goldenrod, dogbane, Queen Anne's lace and more.
To many, a landfill and an unkempt power line right-of-way might look like eyesores. But they're flashing an all-you-can-eat sign for wild bees, which can be found in surprising numbers and diversity in blighted, out-of-the-way spots like this one in Baltimore.
Droege, who heads the USGS native bee inventory and monitoring lab, is working with other researchers to assess their status nationwide amid worrisome losses in domestic honeybee colonies.
The health of wild pollinators is important because they play an underappreciated role in food production, while also ensuring the survival of many of the flowers and trees that make up the natural and man-made landscape.
"If there were zero bees, we would just be eating bread and wine," Droege quipped. While some grains and grapes are self-pollinating, he said, little else is. According to the National Academy of Sciences, three-fourths of the world's flowering plants need pollinators of some kind — including bats and birds — to help them reproduce by carrying pollen from male to female parts of flowers.
There's been growing concern in recent years over honeybee declines, which have been variously blamed on severe winter weather, disease, pests, loss of habitat and pesticides. The Obama administration announced a federal strategy in May to promote the health of honeybees and other pollinators, which called for planting more vegetation on which they can feed, among other measures. Droege welcomed the plan, but said it's based on a shaky understanding, at best, of what's happening with wild bees.
"The whole notion of doing something for conserving an insect is really nice," said Droege. But while everyone now wants to help bees, he said, experts have yet to even identify them all.
"We really don't have a handle on their actual status," Droege said. There is evidence some, notably bumblebees, have lost ground. Honeybees have been extensively studied because of their importance to agriculture, but there's been no comprehensive effort so far to track wild bees. Little is known about many, and the reasons they might be declining are just as murky.
A study published earlier this month found that the ranges of bumblebees in North America and Europe have shrunk over the past century, with many disappearing from their southern reaches. Researchers suggested climate change may be the cause.
Droege wonders if there aren't other factors, but says it's clear something is going on. The rusty-patched bumblebee, once common from Georgia to Canada, has virtually vanished, and conservationists have petitioned the federal government to list it as endangered.
Closer to home, Droege said, one bumblebee that used to frequent Baltimore hasn't turned up east of Frederick for the past couple decades. And a Towson University scientist who's doing a survey of bumblebees in Baltimore County, Droege noted, has found only about half as many species as were recorded in a similar study 30 years ago.
To get a better handle on what's happening, Droege designed a multistate survey of bumblebees this summer. Volunteer "citizen scientists" are collecting bumblebees on federal parklands from the Skyline Drive in Virginia to the Great Smoky Mountain National Park in Tennessee. Researchers hope to find out if any of the increasingly rare wild bees are still hanging out in these remote spots, relatively free of human disturbance and of pesticide use, which some suspect may be affecting bee populations.
The power line right-of-way in northeast Baltimore drew some bumblebees, and even a honeybee or two. But Droege, with Wilson's help, focused on collecting other pollinators, dropping each one in a plastic vial of soapy water for later examination and identification.
Wilson, 41, has been communicating with Droege for several years about the bees he's found as he pursues his own studies of the urban ecosystem.
Armistead Gardens, bordered by landfills, incinerators and toxic-waste dumps, was once dubbed the "Ring of Fire." Those have been mostly cleaned up over the past 30 years, but remnants of the gritty industrial legacy linger. Nature has moved into the gaps.
"I intersected with Thom working on bees," Droege explained, "but he's investigated so many plants and animals in this small area."
Wilson chooses to capture his finds with a digital camera rather than a net — he doesn't like to kill the bees. But he said he has no problem helping Droege build his collection, since it's for science.
"The little bees are usually more interesting," explained Droege. Some don't sting, for instance, and some don't even look like bees. Droege talks about how beautiful they look when their features are magnified under a microscope.
He held up a carpenter bee for inspection.
"See the yellow markings on the abdomen and the bright yellow on the face?" he asked. "You really can't tell how pretty that bee is until you look at it in one of our close-up pictures."
To share his appreciation, he's co-authored a coffee table book just published that features bees-eye portraits of 100 different species, a tiny fraction of the 20,000 found worldwide.
While it's unclear what's happening overall to wild bees, Droege said, there are still many around — even in heavily trafficked or disturbed spots like the power right-of-way.
"Go to the National Mall or Baltimore harbor," Droege said, "and these places are just filled with bees."
Several years ago, Droege and a colleague collected more than 500 bees in a two-day survey of spots around the harbor, including the former steel-making complex at Sparrows Point. Of the 49 species they found, 11 were not native to North America.
While some bees form group nests, others are loners, eschewing life in a hive for a hermit-like hole in the ground or a fissure in a plant. Some are specialists, foraging on only one type of flower — which means it's bad news for them if the host plants disappear. But others, especially those in developed areas, tend to be generalists, Droege said, taking sustenance from whatever flowers they can find.
Ceratina, the carpenter bee, does well in suburbia, the researcher added, because gardeners are frequently trimming plants, and the insect likes to nest in the spongy tissue inside the plants' stems.
For two hours, Droege and Wilson rambled, sharing their knowledge of insects, foliage and — in Wilson's case — local politics. They ventured from the towering landfill to a ridge where new homes are replacing public housing, back down to a beaver-enhanced complex of ponds and swamp, then to Herring Run and back. Birds and green frogs called out along the way, accompanied by a throbbing chorus of cicadas. A pair of deer scuttled across the landfill slope.
Droege eyed the bare hillside.
"Bees like that kind of junky-looking thing," Droege said. "They prefer open dirt."
"The worst possible thing is a very fertilized lawn. It's just too thick, they can't find a place to nest in there."
By the end of the trek, Droege's little plastic vial was nearly black with specimens he'd collected.
"Even today, with a little spitting rain … we have a fair amount of activity," he said. Because trees aren't allowed to grow up beneath power lines, he said, the rights of way are "really awesome spots for plant diversity — and bee diversity."
And while the open area was filled with non-native, invasive plants, the bees — some of them immigrants themselves — love the flowers, wherever they're from.
For example: The broad white array of tiny white blossoms in Queen Anne's lace — a wild carrot introduced from Europe — provide a perfect "feeding platform" for tiny wild bees, Droege pointed out.
After getting back to his lab in Beltsville, the USGS researcher reported that his vial held 17 different species of bees, including seven that hadn't been recorded before in the city.
For Wilson, the haul included four bee species he hadn't seen before near Armistead Gardens. And it grew the total list of bees he's identified in that corner of the city to 78 — "a good day, indeed!" he concluded.
Droege said only one of the bees found, a Texas leaf-cutter, was relatively uncommon. But he said he wasn't surprised to see it, given the habitat. The key, he said, is being there to observe it.
"Spend enough time in the field, like Thom does," Droege said, "and all sorts of nature's treasures are revealed."