Temperature and humidity levels within a home vary significantly depending on location, as basements and cellars are generally moist, while an attic tends to be the driest area within a home. Bathrooms often contain the highest moisture levels of any indoor area, as most single family homes contain multiple residents who each take a daily hot shower. Research shows that every single room and level in a home contains multiple arthropod species, many of which are pests that are not numerous enough to constitute an infestation.

Arthropod species vary dramatically from room-to-room, and especially from level-to-level. For example, insect pests that require moist conditions in order to thrive often congregate in basements and cellars, and this is especially true for slow-moving arthropod pests, like millipedes, that do not have to travel far to gain basement access. Other insect pests that require high-moisture conditions, such as German and American cockroaches, are highly mobile, allowing them to travel to bathrooms where they often congregate beneath the floor and in wall voids near the bathtub, sink and toilet. Understandably, a relatively small number of insect pest species are in the habit of establishing infestations in attics due to the difficulty accessing high levels as well as the relatively dry attic air that most insect pest species avoid.

In the northeast, the most common insect pests that are known for gathering in attics include cluster flies, Asian lady beetles, clothes moths, boxelder bugs, western conifer seed bugs, bed bugs and spiders. Attics often contain stored clothes, stacks of old newspapers or magazines, cardboard boxes, and of course, unpainted wood. Airborne pests typically gain access to attics by flying through vents, and although rare, it is not unheard of for eastern subterranean termite swarmers to establish attic infestations by flying through attic vents. Clothes moths are often found flying around attics while their larvae feed on stored food. Common invasive fall pests, like seed bugs, stink bugs, lady beetles and boxelder bugs, prefer relatively moist conditions, but their eagerness to gain entrance indoors before winter sees these bugs establish a presence in attics where they usually die within a short amount of time. Bed bugs may be present on clothing that is brought into attics, and brown banded cockroaches feed on paper and boxes, provided that a water source is available, such as rainwater leaks. The best way to prevent attic infestations is to install a wire mesh barrier on attic vents, and avoid storing clothes that are infested with clothes moth larvae or bed bugs.

Has your attic ever been infested by cluster flies?