On warm autumn and winter days several species of insects can become a severe nuisance as they congregate on south-facing exterior walls of buildings.  In addition to their large numbers on the outside, they can enter buildings to seek shelter.  Of these nuisance insects, boxelder bugs (a scentless plant bug), are the most numerous.  Leaf-footed bugs and ladybird beetles can also be found seeking warmth and shelter on buildings.  Adults become active on warm days and emerge from hiding places, returning to shelter as temperatures drop at the end of the day. 

            Boxelder bugs are about ½ inch long and easy to recognize because of their distinct coloration: dark gray to black background with red markings on their wings and a red body underneath.  Immature boxelder bugs are smaller and bright red with black legs.  Leaf-footed bugs are larger, 1 to 1 ½ inches long, with a brown body and leaf-shaped “wings” on their hind lower legs.  Leaf-footed bugs can give off an unpleasant odor when handled.

            The main methods to reduce insect populations and their nuisance to you and your home are by cultural practices, exclusion, mechanical removal, and insecticides.  Boxelder bugs primarily live and feed on female boxelder trees which is a species of maple and to a lesser extent on other plants (other maple, ash, fruit trees, grape, strawberry).  They primarily feed on the developing seeds.  Removal of female boxelder trees that produce the winged seedpods can reduce boxelder bug populations if there are not other nearby sources of trees and bugs.  Along riparian areas, tree removal is unlikely to yield results because boxelder trees are too numerous.  The value of the tree must also be considered and may not justify anticipated reductions in insect numbers.  Insecticides can be applied to boxelder trees during the summer when the bugs are young, but again if other sources are nearby, satisfactory results may not be achieved.  Carbaryl (Sevin) and other insecticides registered for ornamental trees can be applied to the trunk and limbs to kill young boxelder bugs.  Leaf-footed bugs feed on a wide range of trees, shrubs, vines, and some herbaceous plants.  Removal of host plants is impractical for control of leaf-footed bugs. 

            Exclusion of insects and mechanical removal are effective non-chemical control methods.  Caulk and seal cracks in foundations, and around windows, doors, and utility conduits.  Remove insects with a broom or vacuum in places where they congregate and after they enter buildings.  Wash them from surfaces with a stiff spray of water from a hose-end nozzle and sweep them up.  Applying insecticidal soap or a homemade solution of mild hand dishwashing soap, such as IvoryÒ, mixed in water (5-10 drops per gallon of water) can deter the insects.  Always test a soap solution on a small area before applying it to a large area.  Soaps can stain certain materials and even etch glass if the wrong type of soap is used.

            There are many insecticides registered in Utah for boxelder bugs and other nuisance insects.  Common active ingredients include carbaryl, cyfluthrin, cypermethrin, lambda-cyhalothrin, permethrin, and pyrethrins.  As with soaps, always test on a small area first to avoid staining or damaging finished surfaces due to oils or other ingredients in insecticide formulations.  Most insecticides applied to exterior surfaces tend to have short residuals because they are rapidly degraded in sunlight and weather.  Adult insects also tend to be tolerant of insecticides because of their thick exoskeletons and ability to disperse rapidly and avoid contact with insecticide sprays.

            Generally the most successful management of boxelder bugs and other insects congregating on exterior surfaces will be achieved by a combination of the above control and exclusion methods and increasing your tolerance to their presence.  The number of days when high numbers congregate is usually brief and they soon will disperse back to their native vegetation.  Visit the Utah State University Extension “Insects and their Relatives” web site for more information on boxelder bugs and other insects:   http://utahpests.usu.edu/insects/.