The presence of the occasional live cockroach in your home or garden doesn't necessarily mean that you have an infestation of the insects, but if you see large numbers of live or dead roaches, shedded skins, egg cases or droppings, you may have a problem. Droppings look like grains of black pepper or coffee grounds; they may also appear as dark smears near the roaches' hiding spots or along their frequently traveled paths. Egg cases are brown, about 1/4 inch long, and oval or rectangular in shape. Large populations of cockroaches may also produce a strong, musty odor that is easy to detect.
Signs of Infestation
Look for these signs in the places where cockroaches tend to nest and feed, using a flashlight or a small mirror to see into dark, tight spaces when necessary. You can also set out sticky traps to help you identify which species of cockroach is present and to give you an idea of how many roaches are living in your home or garden.
Common household cockroach species in the United States include the German cockroach, the brownbanded cockroach, the American cockroach and the Oriental cockroach. Of these, the American cockroach is largest, with a body length of up to 2 inches. The Oriental cockroach is somewhat smaller, with a length of 1 to 1 1/4 inches, and the brownbanded and German cockroaches are both about 1/2 inch long. The German cockroach can be identified by the two dark brown stripes on the back of its thorax.
Species identification is important because different species have different habitat preferences. Knowing which species is present in your home will give you clues about where to look for their hiding places and how to combat them.
Where to Look in the Home
Inside the house, roaches gather and nest in places where there are sources of food and moisture, as well as places where they can stay out of sight. Some species prefer to live in kitchens, where they feed on human food and trash and they are able to hide and lay their eggs in secluded locations. Look for signs of infestation in cracks behind cabinets, under or behind appliances, or near drains or other plumbing.
Some species, including the Oriental cockroach, may also live in bathrooms or basements near leaky or condensation-covered plumbing, in drains, or in wall cavities where there's moisture infiltration.
Where to Look in the Garden
Some cockroach species, such as the wood cockroach, prefer to live outdoors and are rarely a problem in the home. Wood cockroaches, which are common in the eastern half of the United States, often lay their eggs under loose bark on trees and logs, and the adults tend to congregate in moist, dark locations, such as inside hollow logs and under wood piles, where they feed on decaying organic matter. They may also gather under house siding or wood shingles.
Wood cockroaches may migrate inside homes on their own or be carried inside on firewood. Once inside, they tend to wander around the home, but they rarely breed or establish a population indoors.
Insecticidal dusts containing silica, diatomaceous earth or boric acid are often effective in controlling cockroach infestations. Scatter the dust in a very thin layer where the roaches gather and travel, including under appliances, in cracks or places where pipes enter walls. Keep the dust away from places where pets or children play, and do not put it on surfaces used for food storage or preparation. Avoid inhaling the dust, as well.
Cockroach baits contain insecticides which the roaches carry back to their nesting areas, where the poison will kill other roaches. Place the baits in corners and against walls where roaches move and feed, such as inside cabinets, near trash cans and under appliances.