The caddisfly is a winged insect commonly seen in the Janesville area during the summer, particularly near the Rock River. Insect populations tend to explode with heat and rain.


If you’re hoping to enjoy a summer sunset near the Rock River, you’ll have to share it with the caddisfly.

The winged insects, tan-colored with long, curved antennae, are commonly found near water. They don’t harm people or property, but they’ve been antagonizing residents who like lounging on riverside patios or balconies downtown or are visiting Hedberg Public Library or other businesses.

Their populations have exploded recently thanks to high temperatures and recent rainfall.

Library Director Bryan McCormick said he never really noticed the caddisflies before last year. Now he sees them everywhere.

“I know they have been around for awhile, but last year was the first summer that it seemed like they were here all summer long. Prior to that, it seemed like just one or two hatchings,” he said.

Library patrons definitely have noticed them.

“You walk out the back door, and they are literally right there,” McCormick said. “I get home from my drive after work, and I have 10 or so of them still hanging on to the windshield. They have some cling power.”

The library has not done anything about the insects because they don’t cause damage, he said.

Wisconsin has more than 200 species of caddisfly, and the insect is abundant in warmer seasons of the year. They often are seen later in the day after the sun sets and tend to swarm around lights at night. Because they are found near water, fishermen often use baits that mimic their movements.

PJ Liesch, an entomologist at UW-Madison, said people can expect to see caddisflies around until August. He said their presence is a positive sign about the environment.

“Oftentimes, different species of the caddisfly will come and go throughout the summer months, but the fact that they are here actually shows good water quality,” Liesch said. “If the river was highly polluted, they wouldn’t be around.”

Liesch doesn’t have a foolproof way to make the insects go away. He warned against spraying them because they cause no harm, but he did have a suggestion on how to make them more tolerable.

Liesch said most outdoor lights are placed right outside a building and send light outward. He recommends placing lights on a post with the lighting pointed inward toward the building.

“The caddisflies will be drawn more to the bulb than the house. So if you adjust the lighting outside, it will help keep them away from structures and people.”

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