If you’re traveling in the local forests this summer and early fall in Cook County, there’s a chance you’ll notice an otherwise out-of-place purple object hanging from some area trees.

And there is a purpose to these purple prisms. And it's to catch the invasive insect known as the emerald ash borer.

The United States Department of Agriculture recently set up a collection of purple prism-shaped traps in Cook County as part of a study to find out if emerald ash borer has in fact arrived to the local forests. In the past two years, there have been confirmed cases of the invasive insect in both Duluth and Thunder Bay.

The purple trap is a three-dimensional triangle or prism. It’s made out of thin, purple plastic that has been coated with non-toxic glue on all three exterior sides. The purple traps are about 24-inches long and hang vertically in ash trees. Each trap is baited with a lure on the interior to attract ash borer to it.

According to the USDA, in their adult stage, ash borers fly around ash trees, feeding on leaves and looking for a mate. If the insect lands on a purple trap, it will get stuck in the non-toxic glue coating. Survey crews service the traps two times: at some point in the summer to replace the lure and collect any insects stuck on them; and in the fall, to collect any suspect beetles and remove the traps.

To date, there are no confirmed cases of emerald ash borer in Cook County. This could change when the survey is complete in the fall.