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 extinct cockroach relatives and ‘roachoids’ such as the Carboniferous Archimylacris and the Permian Apthoroblattina were not as large as the biggest modern species Etymology
The name “cockroach” comes from the Spanish word for cockroach, cucaracha, transformed by English folk etymology into “cock” and “roach”. The term cucaracha (streak bug, sp.) 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 Americans began using the term for regular (non-flying) cockroach. Cockroaches, like all insects, breathe through a system of tubes called tracheae. The tracheae of insects are attached to the spiracles, excluding the head. Thus, cockroaches, like all insects, are not dependent on the mouth and windpipe to breathe.
The valves open when the CO2 level in the insect rises to a high level; then the CO2 diffuses out of the tracheae to the outside and fresh O2 diffuses in. Unlike in vertebrates that depend on blood for transporting O2 and CO2, the tracheal system brings the air directly to cells, with the tracheal tubes branching continually like a tree until their finest divisions, tracheoles, are associated with each cell, allowing gaseous oxygen to dissolve in the cytoplasm lying across the fine cuticle lining of the tracheole. CO2 diffuses out of the cell into the tracheole.
While cockroaches do not have lungs and thus do not actively breathe in the vertebrate lung manner, in some very large species, the body musculature may contract rhythmically to forcibly move air out and in the spiracles; this may be considered a form of breathing.