By Pat Hottel

One of the many ways that insects survive cold weather is to hibernate in void spaces of structures. They migrate towards buildings in search of an ideal warm resting spot to spend the cold winter. Changes in daylight hours and cooler temperatures can trigger the insect’s indoor movements. Normally there is a single life stage, the adult stage, when the insects move indoors and they do not breed, feed or develop during the winter. They slow down their metabolism and wait for the arrival of spring. Examples of the most common insects employing this survival tactic include: multi-colored Asian lady beetles, cluster flies, boxelder bugs, brown marmorated stink bugs and the Western conifer seed bugs. These insects, by virtue of their numbers alone, can elevate beyond nuisance status, especially in sensitive environments like food-production plants, pharmaceutical plants and health-care facilities where insect contamination is a concern. Some can stain surfaces and create offensive odors in addition to being a nuisance and contamination threat. Here are “the invaders”:

Boxelder Bugs 

Probably the most common of the fall invading insects, this black and red marked bug actually feeds on trees, including the boxelder and maple. It is ½-inch long as an adult, and mostly black in color with red lines marking the wings and the thorax or area behind the head.

Brown Marmorated Stink Bug 

The brown marmorated stink bug is a relatively new invasive insect that has moved from its U.S. introduction point in eastern Pennsylvania westward, causing growing problems for pest management professionals. This is both an agricultural and structural pest. It can be identified by its mottled brown color and shield-like shape. Adults are about 5/8-inch in length and have lighter bands or stripes on the last segments of the antennae and around the exposed edges of the abdomen.

Cluster Fly 

There are several flies that will overwinter in structures. Cluster flies and face flies are the most common and tend to cause the most concern since they often appear in groups or clusters. The adult cluster fly is slightly larger than a house fly. The wings are held overlapping each other over the abdomen unlike the house fly, which has wings that appear to be more of a triangular pattern when at rest. It has golden yellow hairs on the thorax or main middle section of the body. The immature stages are parasitic on earth worms and cause no structural harm.

Multi-Colored Asian Lady Beetle

These beetles get their name because they can vary in color and markings. The wing color can vary from tan to reddish orange and they can have a varied number of black spots on the wings. They are predaceous on soft-bodied plant pests like aphids and have a valuable role in reducing agricultural and horticultural pests. They achieve pest status as they migrate indoors in the late fall months. They are sometimes called the Halloween beetle because they often come into structures around that time on a sunny day after a frost.

Western Conifer Seed Bug 

This bug is a plant pest of conifers where it feeds on sap in cones, seeds and needles. It is ¾-inch in length, reddish brown in color with a faint white zig zag pattern that runs across the mid-section of the wings. It belongs to the leaf-footed bug family, so named because of the flattened leaf-like section on the hind leg. This fall invader is found in the Northern states only.

First Line of Defense (3 Ss) 

The first line of defense are the 3 Ss (sealing, sweeps and screens). Ideal temperatures for their overwintering locations are in the 40-50°F range, typically found in the exterior wall voids or attic spaces of buildings. Denying insects access to these ideal harborage sites is the first line of defense in control. The use of sealants, door sweeps and screens are the primary exclusion tools in preventing entry. The size of entry hole and degree to which sealing is needed will depend on the insect. The multicolored Asian lady beetle will fit through openings 1/8-inch in size or larger. The sealing of all cracks in this width and use of normal window mesh screening will exclude most of the fall invaders. Door brushes and seals also should be in place. All sealing efforts must be made prior to the insect’s indoor migration, so those measures are typically conducted in the summer months.

All of the invaders tend to migrate towards the sunnier sides of the structure, which warrants special attention to sealing in south, west and east exposures. Several of the invaders will orient towards contrasting colors on walls (e.g., where a light colored building meets a dark frame). They also may follow structural lines such as foundation/siding junctures. All of these tips can be used to optimize sealing efforts. The table below shows the estimated time frames for fall-invading insects to move into and out of structures. It can be used to help plan proper sealing times. Seal after they leave the building and before re-entry in the fall or late summer. 

Insecticidal Control

Perimeter treatments with insecticides can be used to supplement exclusion efforts. The applications should be made to areas where the insects are resting and entering the building. New changes in pyrethroid insecticide (i.e., deltamethrin, cypermethrin, cyfluthrin and lambda-cyhalothrin) labels may limit the ability to treat all areas with these products. More directed treatment may be required under the new labels. Pest management professionals may need special lifts or ladders to reach affected areas on structures with impervious surfaces that fall directly underneath the target surface. If insecticidal treatments are performed, they should be scheduled at the time right before the insects are starting to enter the structure for optimal effectiveness. Insecticide treatments after they have entered the structure are of minimal help.

Physical Removal

If the window for exclusion and preventive pesticide treatment was not met and the insects made their way unrestricted, insect light traps may be helpful in attracting and eliminating some of the insects that are not confined in ceiling or wall void spaces. Occasionally, a number of the invading insects will wind up in the occupied spaces of the building based on their point of entry, or they may emerge in winter during a temporary “January thaw” situation, believing that it is spring time. Smaller portable, battery-operated light traps can be useful in small areas for attracting insects and may offer some relief.

Commercially available exterior pheromone traps have been used successfully in reducing brown marmorated stink bugs on the exterior. Care should be used in ensuring they are not placed too close to the structure, which might encourage interior migration.

In addition to light traps, insects also can physically be removed through the use of vacuums. If vacuums are used, the contents should be discarded right after vacuuming has been completed. Some of the invaders like stink bugs can cause objectionable odors if left inside the vacuum.

Pat Hottel, a member of the Copesan Technical Committee, has almost 40 years of experience in the pest management industry. She’s been with McCloud Services in Hoffman Estates, Ill., since 1980 and serves as technical director. Hottel holds a bachelor’s degree in entomology from the University of Georgia and is a BCE.