Feature Articles
Insects Trying to Get Out of Your Home May Cause Alarm
Richard M. Houseman, Ph.D., Department of Entomology, University of Missouri-Columbia
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: Sunday, April 20, 2008
