Cockroaches are insects of the order Blattodea, sometimes called Blattaria, of which about 30 species out of 4,600total are associated with human habitats. About four species are well known as pests.
Among the best-known pest species are the American cockroach, Periplaneta americana, which is about 30 mm (1.2 in) long; the German cockroach, Blattella germanica, about 15 mm (0.59 in) long; the Asian cockroach, Blattella asahinai, also about 15 mm (0.59 in) in length; and the Oriental cockroach, Blatta orientalis, about 25 mm (0.98 in).Tropical cockroaches are often much bigger, and, contrary to popular opinion, extinct cockroach relatives and ‘roachoids’ such as the Carboniferous Archimylacris and the Permian Apthoroblattina were not as large as the biggest modern species.
The name “cockroach” comes from the Spanish word for cockroach, cucaracha, transformed by English folk etymologyinto “cock” and “roach“. The term cucaracha (sp. cuca “bug”, and raxa “streak” (modern Spanish raya)) originally was used for the wood louse (the sow bug), but later was used to mean the palmetto bug (the flying cockroach). It is from this later Mexican usage that English-speaking Americans began using the term for regular (non-flying) cockroach.
(From Wikipedia, February 2015)