By Ann Hazelrigg, Extension Plant Pathologist, University of Vermont
When the weather turns cold, four common insect invaders may appear uninvited in your home. None of them breed in the house or cause any damage to humans, pets, food items, or structures. These nuisance pests are looking for a warm, protected place to overwinter and hibernate.
The western conifer seed bug (Leptoglossus occidentalis) is the largest of the four insects. It feeds primarily on seeds and developing cones of several conifer species. The range of these true bugs (order Hemiptera) currently extends across the northern U.S. into Canada.
Adults are about 3/4 of an inch long, brownish in color, with alternating light and dark bands running along the outer wing edges on each side of the abdomen. The lower hind leg is widened on each side and looks like a tiny leaf has been attached. These insects move slowly and can fly, often making buzzing sounds when airborne, and will give off a pungent odor if you handle them.
The brown marmorated stink bug (Halyomorpha halys) can be confused with the western conifer seed bug but is smaller. It is brownish, shield-shaped, and about 5/8 of an inch long, and the next to last (fourth) antennal segment has a white band. Several abdominal segments protrude beneath the wings, alternatively banded with black and white, hence the term “marmorated.”
This insect was introduced to the U.S. from Asia in 1996 and has become an invasive, destructive fruit and vegetable pest in the mid-Atlantic states. Their numbers have been low in Vermont, and they are considered home invaders as opposed to crop pests. During the several weeks of peak flight, they can enter homes through any small opening. Once inside, they will often fly, causing a buzzing sound. They do not reproduce, damage structures, bite people, or harm pets. They can exude a pungent chemical when they are handled or crushed. Adults mate outdoors in the spring about two weeks after emerging from a resting phase.
The multicolored Asian lady beetle (Harmonia axyridis) is a more colorful nuisance insect introduced by the United States Department of Agriculture (USDA) as a predator of aphids and scale insects. Asian lady beetles are slightly larger than native lady beetles and are oval and yellow to red in color. They can have no spots or as many as 19.
These beetles congregate on sunny south/southwest sides of houses in the fall and can inundate homes from September through April. It is common for tens of thousands of beetles to congregate in attics, ceilings, and wall voids. Due to the warmth of the walls, they will move around inside cavitites and exit into living areas. The little beetles can exude a foul-smelling defensive chemical, which will sometimes cause spotting on walls and other surfaces.
Boxelder bugs (Boisea trivittata) are about 1/2 inch long by1/3 of an inch wide. They are dark brownish black with three lengthwise red stripes on the thorax (area behind the head).
They become particularly annoying in the fall when adults and large nymphs tend to congregate in large numbers, primarily on the southwest side of structures and on boxelder trees. They migrate indoors, and adults overwinter by hiding in cracks and crevices in walls, door and window casings, around foundations, and other protected places. Once inside, they can spot curtains, furnishings, and clothing with their excrement. When crushed, they give off an offensive odor.
They do not breed indoors, and they eventually die when trapped in the house. Removing boxelder trees may decrease their numbers in the fall; however, they can fly up to two miles. These bugs do little damage to landscape or ornamental plants.
Mechanical exclusion is the best control method to keep all of these nuisance pests from entering homes—seal cracks around windows, doors, siding, utility pipes, behind chimneys, and underneath the wood fascia and other openings with good quality silicone or silicone-latex caulk.
Damaged screens on doors and windows should be repaired or replaced. Cover attics, fireplace chimneys, and exhaust vents with # 20 (or smaller) screen mesh.
Exterior applications of insecticides may offer some relief from infestations where completely sealing the exterior is difficult or impossible, but this is usually not warranted.
The use of a vacuum is still the most efficient method of collecting beetles in the home. It is advisable to empty the bag and beetles after each vacuuming.
Dr. Ann Hazelrigg is the University of Vermont Extension plant pathologist and director of the UVM Plant Diagnostic Clinic.
