The German cockroach is by far the most important and usually the most common of the cockroaches. In addition to being a nuisance, it has been implicated in outbreaks of illness, the transmission of a variety of pathogenic organisms including at least one parasitic protozoan, and allergic reactions in many people. This species has worldwide distribution.

Adults are about 1/2-5/8" (13-16 mm) long and light brown to tan in color except for 2 dark, almost parallel longitudinal stripes/bars/streaks on pronotal shield. The female is darker than the male, and her abdomen is broader. They rarely glide or "fly".

With nymphal instars 1-2 the thorax is dark brown to black but has pale lateral margins, the meso- and metathorax are pale/white centrally but have a continuous dark stripe near each margin; the thorax and abdomen are light brown ventrally. Later instars (3rd on) have 2 dark longitudinal stripes on the pronotum and is continuous with dark abdomen and abdominal segments.

Ootheca or egg capsules are yellowish brown but usually two-toned, paler end attached to female; about 1/4-3/8" (6-9 mm) long, with length more than twice width; subdivisional furrows extend the entire width; slightly bowed or arched; and with about 15-20 (range 925) eggs on each side.

The female carries her ootheca until it is within 1-2 days of hatching, and then deposits it in a sheltered area/site. On the average, the female will produce about 5 oothecae (range 4-8), averaging 30-40 eggs (range 18-50) each.

Developmental time (egg to adult) usually varies from 54-215 days, averaging about 103 days; under lab conditions of 80 degrees F/27 degrees C and 40% relative humidity, usually only 50-60 days are required. This means usually 3 to 4 generations per year, but up to 6. Adults live about 100-200 days (range 1-303). Established/mature German cockroach populations are typically composed of at least 75% nymphs.
HABITS. German cockroaches are found throughout structures but show a preference for warm (70 degrees F/21 degrees C) and humid places. They are usually found in kitchens and secondarily in bathrooms, but infestations often occur in rooms where people eat and drink while watching television such as the den, bedroom, etc. Any crack or crevice located near a source of food and/or water is prime harborage, and they spend about 75% of their time in such harborages. First instar nymphs require a crack of about 1/32" (1 mm) whereas, adults require a crack of about 3/16" (5 mm) in width.

These cockroaches are most commonly introduced into buildings via paper products or paper packaging such as grocery bags, cardboard boxes, drink cartons, and via secondhand appliances such as refrigerators, televisions, VCR's, microwaves, etc. They have been observed to migrate from building to building on warm evenings, but this rarely occurs. Although uncommon, they can survive outdoors during the warm months.
They feed on almost anything with nutritive value including all kinds of food, and such things as soap, glue, and toothpaste.

Activity periods vary with life stage, age, and physiological state. For instance, reproducing females are quite active whereas, gravid (with ootheca) females are relatively inactive starting about the 5th day after mating and go only to food and water when necessary. Males spend most of their time in harborage, even at night. All nymphs become immobile and stay in harborage during the last 3 days of each instar while they prepare to molt. Hence, about 1/3 of the time the cockroach nymphs will not be found or found exposed during an inspection.

Information compiled from the National Pest Management Association, Inc. (NPMA)