By Carl Hoffman

Boxelder bugs are gathering on the outside of some homes in large numbers and multi-colored Asian lady beetles will probably arrive soon. Both boxelder bugs and Asian lady beetles congregate on the outside of homes as they search for sites to overwinter. Many of them may find their way into the home and, although they do not feed or reproduce there, they can certainly be annoying.

The large number of boxelder bugs appearing now is due to the weather this summer. Boxelder bugs are just one of many insects that are more abundant during hot, dry summers. These bugs reproduce and feed on female, seed producing boxelder, maple and ash trees. During late summer and fall, boxelder bugs begin leaving the trees to find protected areas for the winter. Although many immature insects may be present in the fall, only full-grown bugs survive the winter. The adult boxelder bugs are capable of flying several blocks and sometimes may even fly further than that. Boxelder bugs like sunny areas and are attracted to buildings with a lot of southern exposure. As weather cools, these insects will push into cracks and enter houses near the foundations. Many crawl under shingles and get into wall voids and attics. They also may enter through doors, windows, vent openings and other accessible areas.

The multi-colored Asian lady beetle has become a nuisance pest in the fall during the last few years. Unlike the common lady beetle, or ladybug, the multi-colored Asian lady beetles like to overwinter in large numbers in and around buildings. Once they find a house they like, they emit a chemical that attracts even more individuals, which can result in congregations of thousands. It is important to note that they do not reproduce indoors so that all lady beetles seen inside during the winter and spring have entered the home during the previous fall. Therefore, preventing them from entering is the most effective step in managing the lady beetles.

The most effective control for these insects begins outside. Prevent the insects from entering your home by carefully sealing as many potential points of entrance as possible. Caulk, seal, or screen gaps in siding and under eaves, vents to the outside, cable and meter attachments, cracks around windows, doors and siding, openings that may exist between the siding and foundation and any other openings that can be found. These insects need only a very small opening to enter, so it is important to check all possible sites of entry very carefully.

Making any necessary repairs will not eliminate all of the insects, but can significantly reduce the number entering the home. If the number of any of these insects is more than you can tolerate, you may wish to use a residual insecticide. Make sure the product is labeled for use around the outside of buildings. Concentrate your efforts on the south and west sides of your home as this is where the insects are most likely to be found. The best time to spray is when you first observe the insects clustering around the outside of your home or other building. Effective insecticides that are available to the public include bifenthrin, cyfluthrin, cyhalothrin, deltramethrin, permethrin and tralomethrin. These products are sold under various trade names. The name of the chemical in the product will be found under the "Active Ingredients" listed on the label. Read all directions very carefully before purchasing an insecticide and again before applying them. Be sure the product you intend to use is labeled for use on the exterior of buildings. Apply the insecticide according to label directions on the foundation, around doors, windows, and along roof lines, paying particular attention to the south and west sides. To be most effective, these residual insecticides should be applied when the insects first begin to congregate on the outside of buildings.

A soap mixture can be used as an alternative to synthetic insecticides in the control of boxelder bugs. Mix 1/2 cup of a liquid laundry detergent in a gallon of water in a hand sprayer or squirt bottle. It is important to test this mixture first on an inconspicuous spot before applying it to the entire area, as it might stain cedar and other siding. Once you determine the mixture to be nonstaining, apply a coarse spray directly on the bugs as often as necessary. It is important to note that the soap mixture affects only those boxelder bugs that are sprayed and does not prevent other bugs from returning to the site. Soap mixtures are not effective in controlling multi-colored Asian lady beetles.

Once these pests get inside, the only practical control is to remove them by hand or with a vacuum cleaner. The use of insecticides indoors is not effective and is not recommended.

- Carl Hoffman is with the University of Minnesota Extension.