Cockroaches are insects of the order Blattaria or Blattodea. The name cockroach comes from the Spanish word cucaracha, chafer, beetle, from cuca “kind of caterpillar.” The scientific name derives from the Latinized Greek name for the insect.
There are about 4,500 species of cockroach, of which about 30 species are associated with human habitations and about four species are well known as pests.
Among the best-known pest species are the American cockroach, Periplaneta americana, which is about 30 millimetres (1.2 in) long, the German cockroach, Blattella germanica, about 15 millimetres (0.59 in) long, the Asian cockroach, Blattella asahinai, also about 15 millimetres (0.59 in) in length, and the Oriental cockroach, Blatta orientalis, about 25 millimetres (0.98 in). Tropical cockroaches are often much bigger, and extinct cockroach relatives and ‘roachoids’ such as the Carboniferous Archimylacris and the Permian Apthoroblattina were not as large as the biggest modern species. They usually live alone only coming together to mate.