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Originally published Monday, September 9, 2013 at 9:05 PM

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Sizzling summer’s final sting: a bumper crop of wasps

Colonies of the largely beneficial wasps and yellowjackets are peaking as summer ends — but think before you swat: alarm pheromones can draw a swarm.

Seattle Times science reporter

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Linda Hamilton would have preferred peaceful coexistence. But the yellow jackets at her Laurelhurst home attacked the crew that takes care of her yard, stinging one man a dozen times.

So she reluctantly called in a strike in the form of Keith Glatzer, owner of the Edmonds-based Wild Bee Company. Glatzer practices an eco-friendly form of pest control, using a vacuum to hoover up wasps instead of dousing them with chemicals.

“I’ve been superbusy this year,” he said last week, as he suited up in full beekeeper regalia before advancing on the two ground-nesting colonies in Hamilton’s front yard. “I’m seeing a lot more colonies, and sometimes multiple colonies in a single house.”

It turns out that Washington’s human inhabitants aren’t the only species benefiting from one of the most splendid summers in years. The warm, sunny weather has also spawned a bumper crop of yellow jackets and other wasps in many parts of the state.

The result has been a litany of conflicts — from stings to ruined picnics — that often end badly for the largely beneficial insects.

In Snohomish County, the Washington State UniversityExtension office has been fielding far more calls than last year, when cool, wet weather seemed to put a damper on the populations, said David Pehling. “This certainly isn’t the worst year we’ve ever had, but it’s higher than average.”

The state Department of Natural Resources has received so many complaints that the agency posted a statement denying a rumor that it releases yellow jackets to control forest pests.

East of Chinook Pass near Mount Rainier, yellow-jacket traps nailed to trees in Forest Service campgrounds are filled to the brim with black-and-yellow corpses. Trail and timber crews have been battling swarms and many workers are nursing red welts, said Leo Silba, of the Naches Ranger District.

But despite their prickly nature, the state’s 15 wasp species serve a valuable function, consuming enormous numbers of flies, caterpillars and other insects considered pests, said Peter Landolt, a U.S. Department of Agriculture research entomologist based in Yakima.

Understanding wasp biology and behavior can help humans live more harmoniously with their winged neighbors, he says. “I’m always rooting for the wasps — but I’m unusual.”

Landolt’s own tolerance threshold was tested when he discovered a colony of paper wasps had set up housekeeping under the gas-cap cover on his Ford Bronco. “Some of these species do really well around people, which is where you get problems.”

Good wasp weather

The biggest headaches are often caused by invasive species, such as the German wasp, a kind of yellow jacket that first showed up in Washington in 1980, but is now widespread. Unlike the native Western yellow jackets, which usually nest underground in abandoned rodent burrows or other cavities, the German variety is equally happy to take up residence inside the walls of houses.

Baldfaced hornets, which despite their name are actually wasps, are the architects of the distinctive, football-sized nests found dangling from trees and shrubs. Their ivory-and-black coloration sets them apart from most of the state’s other common species.

The region is also home to several species of paper wasps. Distinguished by their slender bodies and habit of dangling their legs when they fly, paper wasps build small, umbrella-shaped nests with exposed combs. They’re less aggressive than yellow jackets, but some varieties, like the nonnative European paper wasp, seem attracted to human habitations.

This year’s mild spring and warm summer have been favorable to wasps in two ways, Landolt explained. More overwintering queens survive when the weather is mild, and wasp metabolism and growth rates rev up at high temperatures.

But populations vary widely across the state. In some regions, the insects aren’t particularly plentiful this year, he said.

Invariably, wasps are most troublesome to people in late summer and early fall, as colonies — which originate with a single queen — reach their maximum size.

“Right now, the colonies are about as large as they’re going to get and they tend to be a little more aggressive,” said WSU entomologist Richard Zack. “Maybe you hadn’t noticed that you have some in your yard, but now you’re starting to see a lot more of them.”

Some yellow-jacket nests can swell to 10,000 workers, all female, and all focused on feeding and protecting the larval brood.

That’s why wasps make a beeline for picnic lunches, particularly the meat course. Normally, they would haul insects back to the nest, but ham or barbecued ribs might smell even better and are decent sources of protein. Scientists have actually tried to answer the question of whether wasps prefer fried chicken, sardines, tuna or other human foods, Landolt said. So far, it appears they like it all.

Wasps will also zero in on sweets like rotten fruit, tree sap or cola.

A strong defense

Pehling got nailed on the hand last week when he picked up a soda can and didn’t notice the hitchhiker slurping up the last sticky drops. “I mashed it with my thumb,” he said. “The pain kept me awake until about 3 in the morning.”

Gwen Tollefson, of Lynnwood, was hiking with a friend in the Olympic Mountains when he riled up a colony — and she took the hit, sustaining at least 11 stings. “I didn’t really see them, but all of a sudden I felt this intense burning,” she said. “Many expletives were coming out of my mouth.”

Unlike bees, which can only sting once, wasps are equipped with a syringe-like stinger that can deliver four or five injections before they run out of venom. It’s a defense mechanism, to protect the nest from marauding mammals, Landolt said.

“I’ve seen yellow jackets flying at my head, spraying venom at my face,” he said.

But smashing wasps is not the best defensive strategy — and can, in fact, backfire.

Landolt made that discovery when he was conducting field work in Florida, attempting to collect yellow jackets from a large nest in a stump by sucking them up with a vacuum. Even though he was wearing a protective suit, he had to back away when the colony went ballistic. As he watched the swarm, he noticed they were attacking the opening where the vacuum vented air.

“That gave me the idea that the wasps I had captured in the vacuum were releasing alarm pheromones, eliciting this massive attack,” he said.

Sure enough, when he did controlled experiments in the lab, Landolt was able to isolate and identify the chemical. Wasps emit it when they sting — and when their venom sacs are crushed, whether by a fly swatter, a human hand, or a lawn mower.

But all humans require is a little patience to get past the wasp onslaught. As the weather cools, colonies die out naturally, Landolt explained. “In a couple of months, it will all be over.”

The queens stop producing new workers and lay eggs that will develop into next season’s queens and their male consorts.

After mating, the males die and the inseminated queens find a sheltered spot — under a wood pile, behind tree bark or in an attic — to wait out the winter.

Sandi Doughton at: 206-464-2491 or sdoughton@seattletimes.com

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