[Annual Cockroach Control Issue] Moving Day for Oriental Cockroaches

Features - Annual Cockroach Control Issue

This outdoor-dwelling species of cockroach often moves indoors in the fall.


Editor’s Note: This article was adapted from Techletter, a biweekly publication from Pinto & Associates, Mechanicsville, Md. To subscribe, visit www.techletter.com or call 301/884-3020.

Oriental cockroaches primarily live outdoors. They have a seasonal cycle with only one generation per year. The largest number of adults are present in midsummer.

By late summer, most adults have died and the population is made up mostly of nymphs. In the fall, these nymphs frequently migrate indoors. Oriental cockroaches also can move inside whenever the weather outside becomes too hot, wet, dry or cold, or when populations get so large they run out of space in their outdoor sites.

Appearance and Habits.

The oriental cockroach, Blatta orientalis, is large like the American cockroach, but is very dark, almost black in color, and rather shiny-looking. The adult female is about 1¼ inch (32 mm) long and has short, functionless wing pads. The female and the large nymphs look similar. The male has noticeable wings but they cover only three-quarters of his abdomen, and he doesn’t fly.

The oriental cockroach is not able to climb vertical surfaces like the German cockroach and tends to move sluggishly. Like other cockroaches, the oriental scavenges on garbage, decaying plant and animal materials, on human and pet food, and on sewage (they are frequent residents of sewers).

Oriental cockroaches have a distinctive and unpleasant odor and most people describe them as being “more smelly” than other cockroach species, especially in large numbers. The female carries her egg capsule for about 30 hours, then leaves it in a protected place near a food supply.

Indoor Harborage Sites.

Oriental cockroaches are “peridomestic roaches,” which means that they can live both outside and inside. Orientals are generally found where it’s damp, cool and dark. Once inside, they can survive and breed successfully if they can find an area with enough moisture. For this reason, they are almost always found on the lowest levels of buildings — in basements, crawlspaces, cellars, garages and ground-floor apartments — and this is where you should concentrate your inspection.

You rarely find oriental cockroaches higher than the ground floor. However, they have been known to follow trash chutes or electrical or pipe chases and end up on higher floors.

Orientals will move to the dampest area in a residence or commercial building; that may be a kitchen or bathroom. You also can find them around leaky pipes, drains, under washing machines or refrigerators, or near sinks in laundry rooms. This affinity for moisture is why they are often incorrectly called “water bugs.” If water is available, oriental cockroaches can live for a month without food.