It is Accidental Invader Season Again

Accidental invaders are insects that inadvertently enter homes and buildings from the surrounding landscape. Many species are troublesome during late summer and fall as they move to protected locations to spend the winter.

Accidental invaders are generally harmless to people and property. They do not feed on people, pets, houseplants, stored products, or furnishings. They cannot sting and they do not carry disease. Accidental invaders cannot reproduce indoors. They are nuisances just by their presence, especially when they occur in large numbers.

Here is a review of the common, autumn accidental invaders, followed by some tips for preventing their entry.

Boxelder bug. Common, well known and extremely variable from year to year. Two generations are produced during the summer on seed-producing boxelder and maple trees, as well as other flowers and shrubs.

Multicolored Asian lady beetle. It’s worth repeating that ladybug and lady beetle are the exact same thing. MALB is the newest of the approximately 500 different species of lady beetles found in North America. MALB was originally from eastern Asia or Japan and was first reported in Iowa in 1995. Lady beetles, including the Asian lady beetles, are beneficial in the landscape, garden, or fields where they eat aphids and other insects during the summer. This species becomes a pest as a household accidental invader in mid-to-late October.

Brown Marmorated Stink Bug (BMSB). This is Iowa's newest accidental invader. BMSB was first identified in the U.S. in Allentown, PA in 2001 and first reported in Iowa in 2011. Since then it has been reported in 43 U.S. states and 30 Iowa counties. BMSB nymphs and adults feed on sap from a long list of host plants including many fruits, vegetables, field crops, shade trees, and other woody ornamentals. We continue to track the distribution of BMSB in Iowa and would appreciate your reports of new county records. Please view the linked map. Reports can be made by emailing digital images to

Management of Accidental Invaders

The preferred management for accidental invaders is prevention; stop them before they enter the house. Pest-proof building by installing tight-fitting door sweeps or thresholds, seal openings around pipes and wires, caulk around windows, doors, chimneys, and other construction joints, and keep siding, eaves, and soffits in good repair. In short, make the exterior walls as insect-proof as possible, realizing it will never be perfect.

Residual insecticide sprays can supplement pest-proofing and may be applied by a professional pest control firm or by the homeowner. Insecticide protection is short lived and may have to be repeated during a prolonged fall. Apply insecticide according to label directions to siding, foundation, windowsills, and door thresholds, and to the lawn or landscape for a distance of several feet from the building. Insecticides must be applied before insects begin to enter buildings to be effective (September to mid-October).

It is not effective in most cases to treat trees, garden or crops during the summer to prevent accidental invaders. Insects can travel long distances and may come from the surrounding area. 

Remove insects that have already entered the home with a dustpan or vacuum. A household aerosol spray labeled for this use provides some relief but is not a long-term solution to the problem. Aerosol sprays do not control concealed pests. Use insecticides indoors sparingly.


Links to this article are strongly encouraged, and this article may be republished without further permission if published as written and if credit is given to the author, Horticulture and Home Pest News, and Iowa State University Extension and Outreach. If this article is to be used in any other manner, permission from the author is required. This article was originally published on October 11, 2019. The information contained within may not be the most current and accurate depending on when it is accessed.