By Whitney Cranshaw, Colorado State University Cooperative Extension Entomologist
As days grow shorter and nights colder, insects make their own preparations to survive the Colorado winters.
A few, such as monarch and painted lady butterflies, migrate to the southern states. Ladybird beetles often migrate westward into the mountains, where they may aggregate in masses soon to be covered with a protective blanket of snow. Most insects, however, stay nearby finding cover where they can.
All too often our homes provide just the winter shelter insects are looking for. Several types of invaders take up temporary residence in homes much to the dismay of human occupants.
Boxelder bugs and elm leaf beetles are the most common temporary invaders in Colorado. Both feed on trees (boxelder and elm) during the summer, but stop at season's end. They remain active walking, or even flying about, but they no longer develop and reproduce. They enter a state dubbed "diapause," somewhat similar to a hibernating bear. This allows their survival, until warm spring temperatures and increasing day length signal that food is again present. They then break diapause and resume their normal habits.
Numerous other insects also use diapause as a means of winter survival. Leaffooted bugs, a large, brown cousin of boxelder bugs, commonly invade homes, particularly in the mountains. Cluster flies, the large, lazy flies that careen into windows during late winter, typically move into the upper floors of a home or office. (They are notorious pests in office penthouses.) Psyllids emerging from galls of hackberry trees, yellow jacket wasps and stink bugs are other common insects that often move into homes.
Some of these invasions are short-lived. For example, millipedes and pillbugs ('roly-poly's) may wander indoors during fall and spring wet weather. They are not seeking winter shelter, only a warmer or drier shelter for the moment. Millipedes can't survive the dry environment of the home and die soon after humidity drops, leaving their crusty carcasses lying near windows and throughout the basement.
Spiders and crickets occasionally wander indoors and may try to take up permanent residence. They don't go into diapause; instead they try to tough it out. Although most don't survive well, those that do can be a nuisance.
Control of all these household invaders is similar. First, try to seal them out by caulking cracks indoors along the foundation or other openings. Do this before the insects move indoors, which can occur several months before you observe them. Elm leaf beetles and cluster flies, for example, may start heading indoors by early September, although cold temperatures accelerate migrations.
Insects also can be blocked by spot treatments of insecticides applied to the exterior of the building. To discourage pests that crawl into homes, such as spiders, millipedes and crickets, perimeter sprays around the base of foundations are useful. Spray around openings, such as windows, to control insects that fly indoors, These include elm leaf beetles, boxelder bugs and cluster flies. Commonly used insecticides include Sevin.
Vacuuming is the best way to collect errant insects once inside. (Mini-vacs are a tremendous advance in household pest control technology!)
Although any 'bug' in a home can be unpleasant, keep the situation in perspective. Most nuisance invaders are temporary and non-damaging. Boxelder bugs and elm leaf beetles won't feed on the furnishings, bite the kids, or eat the house plants. Ultimately, they move outdoors or die without reproducing.
Nuisance pests are widespread in Colorado. Their presence in a home does not reflect on your housekeeping. It's not your fault they decided to move in with you.
Photo: Judy Sedbrook
© CSU/Denver County Extension Master Gardener 2010
888 E. Iliff Avenue, Denver, CO 80210
Date last revised: 01/05/2010