CORVALLIS - Despite the buzz about this summer's plague of deadly stinging insects, yellow jacket populations in the Willamette Valley seem about average to the expert who collects them for a living.
"Generally, yellow jacket numbers in summer are related to weather in April, May and June," said Jim diGiulio, who collects venom for pharmaceutical use. "This spring was fairly mild, and the population numbers at this point seem typical of most years."
But no season can be considered mild if you are allergic to the sting of yellow jackets.
"Stinging insects account for between 40 and 100 deaths annually in the United States," said Mike Burgett, entomologist at Oregon State University and OSU Extension Service. "In western Oregon during the summer, most of those stings come from bees and hornets."
Hornets, including yellow jackets, use venom to defend themselves, but in most cases, it is not the toxicity of insect venom that kills people, it is their allergic reaction to that venom, according to Burgett.
DiGiulio collects hornets and yellow jackets whose venom is used to make serum to desensitize people who are allergic to stings. Similar venom from honeybees is relatively easy to collect from commercial hives. But hornets and yellow jackets must be collected from wild nests, and diGiulio is one of a handful of specialists across the country who do the job.
A former entomology graduate student at OSU, diGiulio is an expert in the taxonomy and behavior of yellow jackets. There are about a dozen different kinds of yellow jackets in Oregon, distinguished by size, markings, and habits. The species that diGiulio targets are those few that you are most likely to come across, those that live under your eaves or show up at your barbeque. The serum developed from his collections is specific to these particular species of yellow jackets.
"In the Willamette Valley, we have four common species: two aerial nesters and two ground nesters," said diGiulio. "It's the ground nesters that people most commonly encounter, so that's the kind of venom serum that is most needed. "
The need for venom keeps diGiulio busy collecting insects for three months every year. Dressed in white coveralls, heavy gloves and a bee veil, diGiulio traces hornets to their paper-lined lairs, then vacuums them from the nest and quickly freezes them in dry ice for shipping.
"Yellow jacket nests are like annual flowers," explained Burgett. "They bloom in the summer then they die."
The nest that is begun by a single queen in the spring may have a few dozen workers by June, a few hundred by July, and several hundred by August. By the end of the summer, yellow jacket nests may contain more than a thousand workers vigorously defending their nest and queen.
Unlike honeybees, hornets don't store food in their nests. They hunt for the food they need as their nest develops. So as the nest grows bigger, so do your chances of crossing paths with foraging workers. Most of their prey consists of insects that we like even less than we like yellow jackets, according to Burgett. Mosquitoes, houseflies and the bugs that are eating your garden are all fair game to yellow jackets. Bald-faced hornets, a black-and-white aerial nester, are voracious predators of other yellow jackets.
By September, nest development turns toward creating queens and males. By October, the new fertilized queens will fly off alone to find a protected spot to spend the winter. Those males and the workers that kept the nest humming all summer will die with the first frosts. Only a few new queens will survive the winter. The old nest is abandoned and will not be reused next spring.
So, the yellow jackets that are crashing your picnic now won't be around much longer.
"It is important to remember that these animals are not aggressive, they are just defensive and it is best to give them their space," said Burgett. "Trying to trap them out of your backyard may be like swatting flies in a cow barn."
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Michael Burgett, 541-737-4896