One of the ways insects survive cold weather is to seek the protection of structures. They migrate towards buildings in search of a 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, which moves indoors and they do not breed, feed or develop during the winter. Examples of the most common insects which use this survival tactic include multicolored Asian lady beetles, cluster flies and box elder bugs.
A second group of fall invaders arrive at our structures accidentally. These insects may be attracted to building lighting and may be tied to harvesting of fields. The majority of these are mold feeders which are associated with grain in poor condition. Examples of these beetles include the foreign grain beetle and hairy fungus beetle.
These insects, just by their numbers, 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.
A Review of the Common Invaders:
Box Elder Bugs
Probably the most common of the fall invading insects, this black and red marked bug feeds on trees including the box elder and maple. It is ½-inch long as an adult, mostly black in color with red lines marking the wings and the thorax or area behind the head.
Cluster Fly
There are several flies which 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, whose wings 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.
Multicolored 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. These insects are predaceous on soft bodied plant pests like aphids so 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 the time of Halloween on a sunny day after a frost.
Hairy Fungus Beetle
The hairy fungus beetle is associated with mold and is light attracted. One common species we find in food plants can be confused with the cigarette beetle due to its size, color and shape. It is oval in shape with a three clubbed antennae. The antennae of the cigarette beetle are saw-like in shape and not clubbed.
Foreign Grain Beetle
The foreign grain beetle is a common late summer and fall invader. It feeds on grains in poor condition and the fungus associated with the deteriorating grain. They are 1/16-inch to 1/8-inch in size. They look similar to flour beetles in color and body shape but are typically smaller and more highly attracted to lights. You may find these beetles in large numbers in insect light traps.
First Line of Defense: The 3 S’s (Sealing, Sweeps and Screens)
Ideal temperatures for their overwintering locations are in the 40-50 degrees Fahrenheit range, which is typically found in the exterior wall voids or attic spaces of buildings. Denying the insects access for these ideal harborage sites is the first line of defense in control. Use of sealants, door sweeps and screens are the primary exclusion tools in preventing entry. The table below shows the estimated time frames for the 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.
Fall Invader Timetable: Dates may vary slightly by geographic location
| Insect | Enter Structures | Leave Structures |
| Box elder bugs | September | March-April |
| Cluster Flies | Late August-September | March-April |
| Multicolored Asian Lady Beetle | October | March-April |
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. Timing of the applications can be critical.
Physical Removal
If the window for exclusion and preventative pesticide treatment was not met and the insects make their way unrestricted, insect light traps may be helpful in attracting and eliminating some of the insects which 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 due to their point of entry or they may emerge in winter due to a temporary “January thaw” situation in belief 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.
In addition to light traps, insects can also physically be removed through the use of vacuums. If vacuums are used, the contents should be discarded right after vacuuming has been completed.
About McCloud Services
McCloud Services, based in South Elgin, Ill., is the leader in food protection services throughout the chain of custody – from grain elevator to grocery store. McCloud Services is known for its integrated approach to pest management, specifically designed for the food service industry. Serving the largest food-related brands in the U.S., the company has earned a reputation as the “food protection experts.” McCloud Services has locations in 11 states with nine service centers. For more information, please visit: www.mccloudservices.com.