Q. I have noticed large numbers of orange or red insects collecting around my patio door. When I open the door, the insects fly inside. What are these insects and should I be alarmed?
A. Boxelder bugs are familiar insects to many people. Adult boxelder bugs are about one-half-inch long, black with orange or red markings. Their wings lay flat over their bodies, overlapping each other to form an X. The immature nymphs are smaller and bright red when they first hatch. You can potentially see all stages at any given time.
Boxelder bugs are primarily a nuisance because they enter homes and other buildings, often in large numbers. Fortunately, they do not bite people and are essentially harmless to property.
Boxelder bugs emerge from overwintering sites in the spring. Eventually they move to female seed-bearing boxelder trees where they lay eggs on trunks, branches, and leaves. These trees are referred to as brood trees. During late summer and fall, boxelder bugs begin to leave the brood trees, looking for sites to overwinter. Boxelder bugs are especially attracted to tall buildings with a large Southern or Western exposure. Color does not appear to influence boxelder bugs as they are found on buildings of all hues.
As the weather cools, boxelder bugs push into cracks and spaces around homes. In some cases they end up in the interior of buildings where they are often found around windows. While you may see persistent numbers of these bugs, individuals are short-lived, only surviving for a few days up to a week.
In the spring, all the surviving boxelder bugs that overwintered inside buildings become active. They try to move outdoors but many remain trapped inside.
The best management of boxelder bugs is prevention – so take steps to keep them from entering your home from the start. Repair or replace damaged window and door screens, seal areas where cable TV wires, phone lines, and other utility wires and pipes, outdoor facets, dryer vents and similar objects enter buildings. Unfortunately, houses with vinyl siding provide too many gaps to effectively exclude these insects. Use an all-purpose insecticide labeled for exterior use on homes where these bugs are gathering. You may also consider hiring an experienced pest control service to treat your building’s exterior.
When boxelder bugs are found indoors; the best option is to remove them with a vacuum or a broom and dust pan. Insecticides have limited value indoors and are not usually suggested. Keep in mind that they do not live indoors more than a few days and do not reproduce inside.
Spraying or removing the seed-bearing boxelder trees in your yard is not a practical solution because adult boxelder bugs can fly up to a couple of miles from brood trees. Although you might encounter large numbers of boxelder bugs in a given year, they are not automatically abundant every season.
Source: University of Minnesota extension www.extension.umn.edu/distribution/horticulture/dg0998.html.