Purdue News
Purdue News
'Tis the season of the annual yellow jacket buildup, when a nest begun in spring by a single queen now hums with thousands of worker wasps, all bent on foraging for food, tending the new queens, maintaining the nest and aggressively defending the homefront.
Before concentrating on the relatively hazard-free task of teaching, Purdue University entomologist John F. MacDonald spent 15 years studying yellow jackets, learning their habits and helping people to understand the group of insects.
For example, most people react fearfully to all wasps, but not all are created equally evil. "If you see a lot of traffic in and about a nest, those are social yellow jackets; just one is probably a solitary wasp. Unlike our society, the social ones are dangerous and the loners are harmless," MacDonald said.
MacDonald still serves as a buffer between the wasps and the rest of us, advising parks, college football stadiums and the State Fair on ways to reduce the nuisance and the very real danger yellow jackets pose for an unfortunate few.
"Most people are wary of yellow jackets, and they should be," said MacDonald, who has been stung hundreds of times in the course of his studies. "They can be very unforgiving if their colonies are disturbed and, unlike honeybees, they can sting multiple times."
For most of us, a yellow jacket sting is a painful episode followed by localized swelling and itching, all part of our immune system response to the venom. It also could involve more extensive swelling, such as a finger sting that swells the arm up to the elbow, he said. If you're stung around the mouth and throat, MacDonald advises seeing a doctor, because the swelling could interfere with breathing.
But for about 1 percent to 2 percent of the population, a yellow jacket sting anywhere can mean a major medical emergency, MacDonald said.
For them, the "awesome array of chemicals" in a drop of venom includes those that can induce symptoms that range in severity from slight to life-threatening: hives, feelings of tiredness and impending doom, a stomach ache, dizziness, and difficulty breathing. These symptoms, far removed from the sting site, mean you have become sensitized to the venom. At the dangerous end of sensitivity, the reaction causes a drop in blood pressure and the victim quits breathing.
The onset of symptoms can be delayed as much as an hour or more after the sting, but once the extreme allergic reaction starts, it progresses rapidly, with only minutes before the victim collapses and dies, he said.
Most at risk are those who have become sensitized to the venom because of a previous sting, usually men over age 50. MacDonald said that statistic may be gender-biased because men spend more time outdoors. Very few people have extreme allergic reactions before puberty, which suggests that children may not be as susceptible to wasp venom. MacDonald suggested that anyone who has had more than a localized reaction to a yellow jacket sting should see an allergist to make sure they haven't become sensitized. Those who have become sensitized might want to carry a bite kit during the warm season or have themselves medically desensitized.
Fearing the insect is not the answer, though. Respectful is not the same as panic-stricken, he said.
"If you're so afraid you won't engage in normal outdoor activities, you need to get perspective," MacDonald said. Knowing what sets yellow jackets off and making sure you're not running a backyard yellow jacket fast food restaurant will help you avoid most dealings with the insect.
Avoid colonies. All 3,000 worker wasps in a typical nest are genetically programmed to defend the nest at all costs. Vibrations or other disturbances can send hundreds of wasps swarming into the air to attack anything that moves. It won't take much prodding to set off colony that has been previously disturbed, because the insects stay in a higher state of readiness. MacDonald proved this for himself when he inspected a nest that had been disturbed the day before by a bulldozer. Just walking up to it sent the colony "exploding into my face," he said.
The best form of control is to quit rewarding wasps for coming around. Efficient scavengers, worker wasps forage full-tilt in the late summer for insects and other meat to feed the larvae back at the nest. They develop a sweet tooth for sweets and sugars in late fall, as their task switches to helping the queens build up body fat for overwintering. Keeping garbage can lids tightly closed and keeping food under cover will help, MacDonald said.
"Wasps can become 'entrained,' which means they can learn and memorize the places to go for food," he said. Wasp-tagging studies also showed they'll return at the same time every day. It can take a while before a wasp realizes no more food will show up, and the insect will buzz by for up to three days after you've cleaned it up.
MacDonald also advised destroying colonies in your yard and play areas. Once you find the entrance hole in the ground, return at night and apply a spoonful of Sevin dust around the entrance. Yellow jackets are daylight insects and are much less likely to object to your interference in the evening, he said, and once several hundred workers track back and forth through the pesticide, their end is near. He doesn't recommend flooding the burrow, trying to burn it out or other home remedies: they won't get the whole colony, and then you're left with wet, angry yellow jackets at a DefCon 5 level of alert.
The German yellow jacket takes even more care. This nonindigenous aggressor seems to prefer building its home in our homes, entering through cracks and crevices and building wasp metroplexes behind the drywall and sometimes beyond.
MacDonald knows one family that returned from vacation to find their entire home taken over by yellow jackets, with hundreds sitting in the windows, flying around the kitchen and greeting them at the door.
Even if it hasn't gotten that far, call a pest control professional, MacDonald said. Special equipment may be needed to get an effective chemical deep into the wall void and contact with the colony. Plugging or simply treating the entrance hole may prompt the insects to locate another exit or chew through the drywall into the home.
He calls yellow jackets the "back-to-school pest," because most of the phone calls come when kids are back in class. "That's when the numbers are large enough to get attention, and people think they just moved in." Not so, he said. That nest has been there all summer, there just hasn't been enough of them to notice.
Some other common fallacies:
No, said MacDonald, any way you think about it. Yellow jackets have adapted to survive all of the weather the Midwest can throw at them. Because each nest begins anew each spring from a single queen, weather has no discernible effect on populations from year to year.
Wrong again. The colony may be nesting in the same place, but it's a different nest. Each autumn the nonqueen adults die off, and the queens move to protected quarters for the winter such as a leaf pile, bark strip or rodent burrow. Untended, the paper nest disintegrates. Because wasp populations can fluctuate widely in a region, the presence of wasps this year is no guarantee you'll be visited again next year.
Source: John MacDonald, (765) 494-4582
Writer: Chris Sigurdson, (765) 494-8415; e-mail, sig@ecn.purdue.edu
Purdue News Service: (765) 494-2096; e-mail, purduenews@purdue.edu
