Cockroach, a common household insect pest. Fossil evidence indicates that cockroaches appeared more than 250 million years ago. There are about 3,500 known species. They are found throughout the world. In North America, there are about 60 species, including the German cockroach, or Croton bug; the Oriental cockroach, or black beetle; the Australian cockroach; and the American cockroach.

The cockroachThe cockroach has existed for more than 250 million years.

The cockroach has a flat body with a head that faces downward; long, thin antennae; and long, spiny legs. Cockroaches are usually brown. Most cockroaches are one-half inch to 2 1/2 inches (1.3 to 6.4 cm) long. The largest cockroaches are found in tropical areas, where some reach five inches (13 cm) in length. Cockroaches of most species have wings, but the insects rarely fly; instead they usually travel by running swiftly. Glands near the back of the body give off a disagreeable odor that helps protect the cockroach against predators. The female cockroach lays an egg case, called an ootheca, containing 12 to 25 eggs. The young are similar in shape to the adults.

Outdoors, cockroaches live under such objects as stones and logs. In buildings where they become pests, they hide in places such as cupboards and between walls. They eat a variety of animal and vegetable matter, especially starches and sweets. Cockroaches are controlled primarily with insecticides. Cockroaches are not known to transmit diseases to people, but they may spread filth and leave a foul odor.

Most biologists classify cockroaches in the order Dictyoptera. The German cockroach (Blattella germanica) belongs to the family Blattellidae. The Oriental cockroach (Blatta orientalis), Australian cockroach (Periplaneta australasiae), and American cockroach (P. americana) belong to the family Blattidae.