Cockroaches are among the most common insect pests in homes, schools, and businesses. They like to eat many of the same foods we do and are especially troublesome wherever food is prepared or served. They also may transfer disease-causing organisms. Fortunately, cockroaches can be controlled with a little knowledge about their biology and behavior, attention to sanitation, and effective use of commercially available insecticides.
Cockroaches have flattened bodies and heads that, when viewed from above, are concealed by a plate-like structure called a pronotum. They move surprisingly fast with their elongated, spiny legs. Their long, thin antennae help them find food and feel their way in the dark (which is when they are most active). Cockroaches can be brown, black, tan, reddish orange, or pale green. Most have wings, and in some species they are short and non-functional.
The most common types of cockroaches in Texas are the American cockroach, Periplaneta americana; German cockroach, Blattella germanica; Oriental cockroach, Blatta orientalis; and Smokybrown cockroach, Periplaneta fuliginosa. German cockroaches spend their lives indoors. American cockroaches are long-lived, reaching adulthood and sexual maturity in an average of 600 days. As adults, they usually live 1 to 2 years.
American, oriental, and smokybrown cockroaches live mostly outdoors but may move indoors in search of food or water. Cockroaches also infest homes when brought in with groceries or boxes, and, once established, can readily move within structures such as from apartment to apartment.
American cockroaches, also known as waterbugs or palmetto bugs, are more common in commercial buildings and are one of the most common cockroaches in sewer systems. The largest cockroach in Texas, it can grow 1 1/2 to 2 inches long. Both the adult male and the female can fly. Adults are reddish brown, with tan to light-yellow bands outlining the pronotum. Young nymphs are grayish brown, but after the first few molts, they become more reddish brown.
German cockroach adults are 1/2 to 5/8 inch long and are light brown with two dark stripes on the pronotum. Both males and females have wings extending to the end of their abdomens but they do not fly. Nymphs have wing pads and two dark stripes extending down the entire thorax and abdomen.
German cockroaches are the most prolific of indoor cockroaches and can produce a generation in about 100 days. They are one of the most widespread insect pests to public health in urban homes, apartments, and restaurants. They transport germs and are associated with allergies and asthma.
German cockroaches do not live outdoors in Texas. The Asian (Blattella asahinai) and field (Blattella vaga) cockroaches look very similar to German cockroaches and may be found outdoors in some areas of the state.
Smokybrown cockroaches are also large. Adults reach 1 1/4 to 1 1/2 inches long. They are dark brown to black and their wings extend beyond the abdomen in both sexes. Their antennae are as long as or longer than their bodies. Younger nymphs are black with two white bands on the body and white-tipped antennae; older nymphs are uniformly reddish brown.
The smokybrown cockroach is common outdoors, especially in the more humid areas of Texas and other southern states. They prefer living in protected, moist, warm sites, away from moving air. Common habitats are ground cover, mulch, palm fronds, soffits, eaves of attics, and tree holes. Smokybrown cockroaches reach maturity in an average of 600 days, and adults typically live 3 to 9 months.
Oriental cockroaches are dark brown to black and grow to about 1¼ inches long. They do not fly and their wings remain short, even as adults. The female’s wings are smaller than the male’s, which extend only slightly over half of the body. Nymphs are uniformly reddish brown to black. The development time from egg to adult averages 575 to 600 days and adult oriental cockroaches live 1 to 6 months. They prefer cooler, ground-level sites such as basements, crawl spaces, and wet areas.
Turkestan cockroaches, Blatta lateralis, are becoming more common in Texas, especially in western parts of the state. Males and females look strikingly different. The brownish yellow adult males are 1/2 to 7/8 inch long. The pronotum has a pale margin, as do the upper corners of the front wings. The female Turkestan cockroach is similar to the oriental cockroach—shiny, dark reddish brown with short wings. However, the outer bases of the wings are pale like the male Turkestan cockroach.
This species is native to Asia but was introduced to California and is expanding its range into Texas. It has become one of the most common outdoor cockroaches in El Paso, where it is found in compost, leaf litter, and potted plants; in expansion joints of sidewalks; and around water meter boxes.
Cockroaches have a three-stage life cycle: egg, nymph, and adult. Mature females produce 12 to 36 eggs at a time, depending on the species. The eggs are protected in a bean-shaped capsule, or ootheca (oh-oh-THEE-kah). The number of oothecae that females produce depends on the species. The female cockroach carries the egg capsule until it is mature or she finds a secluded spot to glue it to a surface or drop it. Some females carry it until just before the eggs begin to hatch. After hatching, nymphs tend to stay in dark, protected cracks and crevices, which they often share with adult cockroaches.
At average indoor temperatures, it takes a German cockroach nymph 50 to 60 days to develop into an adult. The optimum temperature for German cockroaches is around 80 degrees F. Warmer temperatures shorten their development time and increase the potential for population growth.
Most cockroach species are nocturnal—they hide during the day and come out at night to look for food. For example, the German cockroach spends about 75 percent of its life in narrow cracks and crevices, from 1/32 to 3/16 inch wide. From these harborages, adults emerge at night to search for food and water.
If you see cockroaches during the day, it usually means there are a lot of them around. They tend to congregate near sources of heat and moisture, which accelerates their growth and reproductive rates.