WSU News

Close encounters of the wasp kind

yellowjacketYAKIMA, Wash. – As August wears on and wasp colonies reach peak size, sun worshippers and picnickers beware: One rolled-up newspaper swat at a yellowjacket crawling toward that spilled ice tea or platter of grilled hamburgers could unleash a flying armada of angry co-workers if a nest is nearby.
 
When a yellowjacket is smashed, its venom sac releases an alarm chemical that alerts nearby guard wasps to come and defend, according to Peter Landolt, a research entomologist with the U.S. Department of Agriculture in Yakima and adjunct faculty member at Washington State University. Even the process of stinging releases the signal, inciting more wasps to give chase.
 
Peter Landolt
Landolt

With 15 different species in Washington state alone, wasps are seen hovering over grass, landing atop bird feeders and scuttling across picnic tables more and more at this time of year. They’re not seeking people to attack, explained Landolt. Instead, they’re searching for food and water for the developing larvae being cared for at the nest.
 
“August and September are typically when encounters with humans go up. I like to tell people that it’s helpful to understand why wasps behave the way they do to reduce those kinds of encounters,” said Landolt, who in 1987 discovered wasps’ nifty alarm chemical signal – a type of pheromone. He has since designed commercial and do-it-yourself traps with food-based chemical attractants to reduce wasp numbers in areas where people congregate.

Ouch factor
To be sure, there’s a reason grown men and women yelp and even scream when stung. Unlike a honeybee that only stings once, a wasp can repeatedly plunge its stinger into a subject’s skin, injecting more venom each time.
Besides scaring the wits out of us, “stings can be painful and, in some circumstances, dangerous,” said Landolt, especially if someone is allergic to the venom or is stung numerous times by a swarm.
 
But painful encounters can often be avoided, making it a win-win for humans and the wasps trying to raise their young and protect their colonies.
And though it may surprise those of us who’ve been on the receiving end of a wasp’s stinger, these insects play a respectable role on the planet by eating caterpillars, flies and other bugs that damage certain trees, crops and garden plants.
Name that wasp
It helps to know which wasp species is buzzing about, said Landolt. The Northwest is home to lots of yellowjackets and paper wasps, which, with their yellow and black markings, look similar to the untrained eye but are dissimilar in a number of ways.
paper waspBecause paper wasps are less aggressive when threatened and build much smaller nests, they’re generally less dangerous than yellowjackets, he said. They construct small umbrella-shaped nests with the combs exposed – often inside eaves, pipes and window casings and underneath awnings. (Landolt recently discovered a paper wasp nest under the gas cap cover of his Ford Bronco.)
 
By contrast, most yellowjackets build their nests in the ground, including inside rodent burrows.  The enclosed structures, resembling drab-colored Japanese lanterns, are designed to hold many more occupants than those of paper wasps.
 
“Serious encounters arise when a human gets too close to a nest or accidently steps on one,” said Landolt.
bald-faced hornet nestBald-faced hornets – which curiously are wasps and not hornets – are also found in this region. Identified by their ivory and black colored markings and stripes, they build large, bloated football-shaped nests attached to trees and shrub branches. Like yellowjackets, bald-faced hornets mount coordinated, persistent assaults upon perceived invaders.
 
Paper wasps, yellowjackets and bald-faced hornets all produce new colonies each year. Except for a few wasps that might sneak into the warmth of a home, only the mated queens survive the cold months of winter.
Here to today, gone…
All those wasps poking about in gardens and crash-landing on open soda cans?
 
“Come winter, they’ll be gone,” said Landolt.
 
So if possible, keep your cool in their presence and let them eat your insect pests. However, if wasps pose a stinging risk because of their nests’ proximity to people, “by all means, do something about it,” he said.
 
To learn about your options – with diagrams to boot – see “Yellowjackets and Paper Wasps,” written by Landolt and fellow entomologist Arthur L. Antonelli for WSU’s Cooperative Extension Service, at http://cru.cahe.wsu.edu/CEPublications/eb0643/eb0643.pdf