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Insects trying to get out of your home may cause alarm

Richard M. Houseman, Ph.D., Department of Entomology, University of Missouri


In most cases, you get concerned about insects coming into your house. Sometimes, however, an insect problem can be caused by insects trying to get out! This situation might sound unusual, but it happens every spring when outdoor temperatures begin to increase.
 

Why are insects suddenly appearing in my home this spring?
 

All insects must survive the cold winter months. Some insect species congregate together in large groups as temperatures drop during fall, and seek out locations where they will be protected during winter. Once cold weather is past, they become active again and disperse away from their protected areas.
 

If an insect 'congregation' selected your home to pass the winter, and they were able to get inside through cracks, crevices, vents, or poorly fitting screens and doors, their spring migration may leave them trapped inside your home. Two insect species, the boxelder bug and the multicolored Asian lady beetle, are commonly trapped indoors during the spring and will often appear during late March to early April.
 

What kinds of insects usually get trapped indoors during the spring?
 

Boxelder Bug (Boisea trivittata)

This bug is approximately 1/2" long. It is mostly black with red lines on its back. Immature stages are mostly red, with black legs and head. These bugs are plant feeders and feed almost exclusively on female (seed-bearing) boxelder trees (Acer negundo). They may also be found on female silver maple trees (Acer saccharinum). They do not feed on male trees, but may occasionally feed on the fruit of apple or plum trees.
 

Boxelder bugs invade homes in October and November and congregate in wall voids and other undisturbed locations. When crushed, they produce a strong odor. Their feces can cause a red stain on curtains, walls, clothing, and other resting places. They have been reported to bite occasionally, which causes a skin irritation and a red spot resembling an ulcer. Adults become active and move outdoors in spring when the boxelder buds open.
 

Multicolored Asian Lady Beetle (Harmonia axyridis)
This lady beetle is approximately 1/4" to 3/8" long and comes in a variety of colors ranging from beige to yellowish-orange to dark reddish-orange with between 0-19 black spots on their body. The area behind the head and in front of the wings is ivory colored with a black M-shaped mark. They are very beneficial insects that feed on several pests of horticultural plants and crops. Adults may live for up to three years.
 

Asian lady beetles invade homes during October and November and congregate in dark, undisturbed locations such as wall voids or attics. When they become active in March or April, large numbers of them may be seen crawling on walls and ceilings inside the home. They do not sting, carry disease or bite. They have not been observed feeding on wood, cloth or stored food items in the home. If these beetles are handled, they will release a defensive chemical, which has a mild odor and may stain walls and fabrics.
 

What should I do now?
 

If these insects appear in your home during the spring, it is too late to solve the problem for this year. It is better to wait until summer and begin preventing next year's invasion. You can provide immediate relief by using a vacuum cleaner to remove insects that are trying to get outside. If you decide to use the vacuum, remember to remove and seal the vacuum bag immediately. This keeps the insects from escaping and prevents the insect's odorous defensive secretions from contaminating your vacuum cleaner.
 

No attempt should be made to kill these insects while they are passing the winter in wall voids or attics. Killing them without cleaning out all of the dead bodies would provide a food source for scavenger insects like larder beetles and carpet beetles to get established. If these beetles are established, they are a bigger problem than either boxelder bugs or lady beetles because they will infest stored products, fabrics, etc.
 

How do I prevent another infestation next year?
 

Long-term control of boxelder bugs and multicolored Asian lady beetles begins outdoors. Although total exclusion is not realistic, all exterior openings should be considered as possible routes of entry and covered in some way to keep these insects out. Seal cracks and crevices that allow these insects to gain access to interior wall voids or attics. Caulk around cable entrances, window frames, doorframes, overhangs, facia boards, etc. Vents, weep holes, etc. that cannot be sealed should at least be covered with 16-mesh screening. These steps should be taken in June or July to prevent invasions later this fall.
 

Since lady beetles are beneficial insects, no direct control is recommended. However, it will be helpful to reduce populations of boxelder bugs outside your home. Removing boxelder and silver maple trees around your home and neighborhood will reduce populations of this insect. In cases where homeowners do not want to remove these trees, infested trees can be sprayed with an appropriately labeled insecticide. The application should be made to trees during the spring, just after the young bugs have hatched from their eggs. Such treatments require special equipment and a license, so contact a company that specializes in treating ornamental plants.
 

In some situations, preventative chemical barriers may be applied around the home prior to invasions in the fall. They are applied to all outside walls and adjacent overhangs. However, without sealing exterior openings, these barriers provide only temporary relief. In these cases it is useful to contact a pest management professional for this service.

 

 


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Last update: Monday, March 29, 2010