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On yellow alert: Wasp totals boom in late summer

Encounters with things that sting are a part of living in the Inland Northwest.

The searing pain of a wasp attack can make grown-ups scream, jump about and pull clothes off while swatting aimlessly.

The rain clouds that arrived late this week ended a run of hot weather that enabled the region’s three main species of wasps – yellow jackets, paper wasps and bald-faced hornets – to reach their peak numbers, said Pete Landolt, a research entomologist for the U.S. Department of Agriculture in Yakima.

“We had a stretch of weather this spring where it never really warmed up. We had high mortality of nests during that period and the numbers fell off,” said Landolt, who studies wasps. “Then we hit the really hot weather at the end of June. That weather has been ideal. So the ones left have been growing and reproducing like crazy.”

Spokane County Park Ranger Bryant Robinson said his yellow-jacket traps have been filling up regularly with “the buggers” at Liberty Lake Regional Park.

“I would say it seems to be a stellar year for the Western yellow jacket. They are getting into our campers’ meals and stinging people,” Robinson said. “We have staffers being stung, campers being stung. It seems more intense than years past.”

Landolt, though, said even with the ideal conditions he estimates the 2013 wasp population is average.

“Last year was abnormally weak for the poor wasps,” Landolt said. “I would call this a normal year. I have seen years here where they are far more abundant this time of year.”

Know thy enemy

Most stings are immediately blamed on yellow jackets, the ground-nesting wasp with a notorious reputation.

Often the blame is misdirected, Landolt said. Most nests encountered by homeowners are the clamshell-shaped dwellings of paper wasps. They build nests under the eaves of roofs and other covered locations. The individual chambers for larvae are visible, and the wasps – which have similar color to yellow jackets – have longer legs that sag as they fly and a pronounced hourglass body shape.

The second type of visible nests is the rounded – Landolt described them as football-shaped – homes of bald-faced hornets. The gray-colored nests, built in trees or bushes, are distinguishable by the single opening at the bottom.

Bald-faced hornets tend to be bigger than their close relatives, the yellow jackets, he said. And they tend to be darker than the other wasps.

Yellow jackets build their nests underground. If they were visible, the nests would resemble the single-opening nests of the bald-faced hornet, Landolt said.

Each species of wasp has a hollow stinger, which actually is a modified egg-laying device, and can sting multiple times. Each wasp has a venom gland that pumps the chemical into the skin. The sting can do as little as leave a mark, or it can cause an allergic reaction ranging from a swollen bump to life-threatening anaphylactic shock.

“They are all the same general design,” Landolt said. “Bigger wasps can give you a bigger load” of venom.

Therein lies the sting

Wasps don’t go looking for a fight. They can react with legendary vengeance to what they perceive as a threat to their nests, Landolt said.

“What ticks them off can vary,” he said. “It’s hard to tell when they attack if it’s the species or the incident.”

All species of wasps start nests with a single queen.

She does everything: builds the nest, feeds the larvae and cares for the wasps that will become her workers and expand the nest. With a run of hot weather, that process accelerates and the population explodes.

By the end of the summer, wasps note the shorter days and quit making workers and then start laying eggs for drones and queens that will become the breeding population for the next summer.

“As a result, they respond more aggressively later in the season. We think that is because they have more to protect,” he said.

Each species differs somewhat in what can trigger an attack.

“Once disturbed, they may respond more aggressively the second time around,” he said. “Lawn mowers are bad for that. If you are riding a lawn mower along a hedge, from their standpoint you are shaking the hedge and they will respond aggressively to that.”

Unlike paper wasps and bald-faced hornets, yellow jacket nests often remain hidden underground. “They can knock the daylights out of you if you mow over them,” Landolt said.

The region is home to both native Western yellow jackets and non-native German yellow jackets, which were first discovered near Tacoma in 1980, Landolt said.

Both live underground and follow the same life patterns except for one major difference: German yellow jackets make much bigger nests.

“If you disturb a nest of 100 Western yellow jackets and 20 come after you, it’s much less dangerous than if you disturb 1,000 (German) yellow jackets and 200 come after you,” he said. “Because there are more of them, they are just more dangerous.”

Airborne bug killers

Despite their painful reputation, Landolt said, all species of wasps perform an immensely important role in the ecosystem: They hunt other insects.

“I’ve got a vegetable garden, and paper wasps are always hunting for caterpillars and other insects,” he said. “They are keeping a lot of insects off my vegetables.”

In the region’s forests, wasps attack everything from flies to defoliating caterpillars, pine beetles and bark beetles that attack trees. “Their impact for controlling insects is very important,” he said.

Because of that, Landolt said he advises homeowners to avoid nests if the wasps are not causing a problem.

Homeowners can eliminate problem nests in several ways. Landolt said spray insecticides – some fire up to 20 feet – can be very effective at killing off the entire colony of small nests.

Any human attack on a wasp nest should be conducted in the morning when the wasps are present and tend to be less active. “If you wait until late in the afternoon, only 20 to 30 percent of them will be there,” he said.

If campers or homeowners can’t find the nest and want to reduce the numbers of wasps, several commercially sold hanging traps use chemical attractants to lure wasps to their death. Some home remedies are also very effective, he said.

“Fermented apple juice is widely used and generally attractive to lots of types of wasps,” he said.

Meat, such as bacon, fried chicken or even sardines, works like a magnet to attract those yellow jackets most likely to invade camp breakfasts or backyard barbecues, Landolt said.

“The worst pests … the ones that make the biggest nests and sting the most and live the longest in the fall, are going for meat,” he said.