For a few hours Wednesday night, insects in parts of Bloomington-Normal were of biblical proportions.
Swarms and swarms of small, ant-like, winged insects covered cars, pestered dogs, forced some people to move indoors, and they all — seemingly — appeared out of nowhere.
And then they were gone.
Without seeing one up close, he can’t know for certain, but Illinois State Entomologist Chris Dietrich said there’s a good chance that the thousands of insects that briefly plagued Bloomington-Normal were flying ants.
“This time of year, colonies of ants tend to produce winged individuals that go off and form new colonies — it’s basically the males and females getting together to mate and then the females go off and drop their wings and then they establish a new colony,” Dietrich told WGLT. “This time of year, they’re mostly just looking for a place to spend the winter, but since the weather is still pretty warm, they could potentially go ahead and start forming a new colony after the males and females court and mate.”
It’s also possible that the bugs could have been soybean aphids, Dietrich added, but what most people reported seeing resembled winged ants more than anything else.
Either way, warm, humid conditions coupled with rain create favorable conditions for certain insects to reproduce.
“There can be a lot of different species that respond positively to the kind of weather conditions that we’ve had this summer. Really warm weather, lots of rain, lots of humidity — that tends to really promote insect reproduction and they can build up in huge numbers over the course of the summer,” Dietrich said. “Then you see these outbreaks and swarms.”
For some people, the persistent presence of insects en masse may prompt a desire to eliminate them via pesticides or other, contact-killing sprays. Dietrich said he doesn’t recommend such actions, since contact-based sprays only solve part of the issue, and the swarms are usually a temporary phenomenon; in Bloomington-Normal, they lifted after a few hours.
“You might kill a few of the bugs, but then there’s just going to be more. They come back. What really helps is to understand what kind of bugs they are in the first place and whether they’re actually harmful,” he said. “They may be annoying for a while, but generally, they’re going to disappear after a couple of days.”
Whether winged ants or soybean aphids, Dietrich said neither of those insects pose harm to humans (though regarding the latter, soybeans are, obviously, at-risk).
Emerging at irregular intervals and in mass numbers is a strategic move for insects seeking to avoid predators: The numbers overwhelm the potential predators and disappearing after a short time ensures the predators cannot, or struggle to, track their potential prey. Insects’ life cycles are so complex, their species so diverse and their enemies so numerous it makes predicting the emergence of swarms like the one that hit Bloomington-Normal on Wednesday difficult at best.
“You can make some educated guesses based on the conditions at the time, but you can be wrong,” Dietrich said. “Most entomologists, myself included, don’t really try to make predictions like this because we’re often able to be proven wrong.”
Dietrich has been the state entomologist since 2013. The position is the byproduct of the state legislature legally chartering the Natural History Society of Illinois in 1861, though it was formed and originally housed at Illinois State University in 1858.
Now called the Illinois Natural History Survey, its staff, library and research collections were eventually moved to Champaign-Urbana under the umbrella of the University of Illinois where they remain.
