Boxelder bugs are a common occurrence in southeast Idaho. These nuisance pests will soon begin congregating, particularly on southern-facing trees and walls as they gather in areas warmed by the sun. This is a prime opportunity to reduce their populations. Your efforts won’t eliminate them but may reduce your grief as fewer are around to find their way inside homes and other structures. They will soon be seeking safe harbor from the cooling temperatures.
Boxelder bugs that do get inside residences do not feed or reproduce, but their liquid feces can leave unsightly stains. They pose no human health risks. The most common nuisance is the mess the dead bugs leave as they become trapped between windows, in vehicles and elsewhere.
Insecticides, particularly Tempo (beta-cyfluthrin), can be effective as a barrier around buildings. You can apply this yourself or hire a professional. Treat a 2-3-foot swath around the exterior of buildings, particularly anywhere insects may find access such as windows and vents. Vinyl siding is a favorite of boxelder bugs as they can get behind it and survive the winter. Treat corners where the siding ends to reduce this.
Another simple solution is to spray the insects with soapy water. The soap disrupts their cell membranes and breaks down protective coatings. To be effective you must directly coat the bugs with the soap solution. Now is a relatively easy time to accomplish this when they are congregated.
There are several recipes for this soap solution. Utah State suggests ½ cup laundry detergent or 5 tablespoons dish soap with 1 gallon of water. Colorado State recommends a 2-3 % solution of dish soap and water for treating areas with live foliage. There are also insecticidal soaps you can buy that are intended for insect control. Regardless of the formula, you must coat the insects thoroughly.
Learn more about boxelder bugs at: University of Idaho: https://www.extension.uidaho.edu/publishing/pdf/CIS/CIS1155.pdf
Utah State University: https://digitalcommons.usu.edu/cgi/viewcontent.cgi?article=1863&context=extension_curall