Box Elder Bugs

What is black and red and gathers in large numbers on the sunny sides of homes? The answer is boxelder bugs. Boxelder trees in the East are commonly called Manitoba or soft maples. These insects are a major pest of soft maple trees feeding primarily on fallen keys in the early spring and the newly forming leaves later on. Boxelder bugs only feed on the female tree. Female trees produce keys, the male trees do not. Like many other insects, they look for places to over winter and homes and other buildings provide an ideal location.

Boxelder bugs are about 10-14mm ( ½ inch) long and are black with red markings. The young or nymphs are similar to adults but lack wings and are redder in colour. Like pine seed bugs and stink bugs they can give off a strong odour if crushed. These insects are primarily a nuisance pest as they do not do any damage to the home. Problems usually result when they are crushed causing staining and an unpleasant odour. Boxelder bugs congregate on the sunny, sheltered sides of homes in the early fall and as the weather gets colder, will enter into the structure through cracks and crevices. They can congregate in extremely large numbers and in some cases can cover entire walls.

Control and Treatment

Control should begin with sealing and caulking of gaps and openings on the exterior. Cleaning up litter close to the house such as piles of leaves, grass, dead flowers, fire wood and lumber helps reduce harbourage sites. In cases of a light infestation, control is often not necessary as population levels vary from year to year and they are usually gone from the home by late spring. If chemical control is to be done, it should be done on the outside, concentrating on the surfaces and cracks and crevices where they rest. Treatments can be done in the spring and/or fall.

Treatment Schedules

Fall Treatments

Fall treatments should be done when the insects are first starting to congregate and before they penetrate into the structure.

Spring Treatments

Spring treatments canbe done when the over wintering insects are emerging and starting to fly to the trees. Treatment of trees should be done in the spring when the newly hatched young are beginning to feed or in the fall just as the adults start to look for places to over winter. Treatment of trees is often difficult for the homeowner due to the large size and numbers of trees that may be present. As well, the trees may be located on surrounding properties and therefore treatment may not be possible. In some cases if the problem is severe and persistent from year to year and there are only 1 or 2 female trees it may be easier to have them cut down.

A pub that I looked after for many years was ringed by soft maple trees on the neighbouring property. In years of heavy infestations, patrons in the fall were not amused at having to pick boxelder bugs out of their Guinness. The problem was ultimately solved when the neighbour had the trees cut down. In the home, use a vacuum to remove them. Try not to squash them as they may stain carpets or drapes.