More than 4600 species belong to the order of cockroaches (Blattodea). Their representatives occur worldwide. Cockroaches are nocturnal and are mainly found in the tropics and subtropics.
The best studied cockroaches in dwellings as sources of allergens are the German cockroach (Blattella Germanica), which dominates in number in America, the American cockroach (Periplaneta americana), and the Oriental cockroach or common cockroach (Blatta orientalis). The infestation of containers transported by ship or air causes the spread of another cockroach species in Europe, Periplaneta fuliginosa. Periplaneta fuliginosa was originally only native to Japan, Southeast Asia and the Southeast states of the USA.