Feature Articles - Housing
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
