Cockroaches (or roaches) are a paraphyletic group of insects belonging to Blattodea, containing all members of the group except termites. About 30 cockroach species out of 4,600 are associated with human habitats. Some species are well-known as pests. The cockroaches are an ancient group, with their ancestors, known as "roachoids", originating during the Carboniferous period, some 320 million years ago. Those early ancestors, however, lacked the internal ovipositors of modern roaches. Cockroaches are somewhat generalized insects lacking special adaptations (such as the sucking mouthparts of aphids and other true bugs); they have chewing mouthparts and are probably among the most primitive of living Neopteran insects. They are common and hardy insects capable of tolerating a wide range of climates, from Arctic cold to tropical heat. Tropical cockroaches are often much larger than temperate species. Modern cockroaches are not considered to be a monophyletic group, as it has been found based on genetics that termites are deeply nested within the group, with some groups of cockroaches more closely related to termites than they are to other cockroaches. Some species, such as the gregarious German cockroach, have an elaborate social structure involving common shelter, social dependence, information transfer and kin recognition. Cockroaches have appeared in human culture since classical antiquity. They are popularly depicted as dirty pests, although the majority of species are inoffensive and live in a wide range of habitats around the world. Taxonomy and evolution Cockroaches are members of the superorder Dictyoptera, which includes the termites and mantids, a group of insects once thought to be separate from cockroaches. Currently, 4,600 species and over 460 genera are described worldwide. The name "cockroach" comes from the Spanish word for cockroach, cucaracha, transformed by 1620s English folk etymology into "cock" and "roach". The scientific name derives from the Latin blatta, "an insect that shuns the light", which in classical Latin was applied not only to cockroaches, but also to mantids. Historically, the name Blattaria was used largely interchangeably with the name Blattodea, but whilst Blattaria was used to refer to 'true' cockroaches exclusively, the Blattodea also includes the termites. The current catalogue of world cockroach species uses the name Blattodea for the group. Another name, Blattoptera, is also sometimes used to refer to extinct cockroach relatives. The earliest cockroach-like fossils ("blattopterans" or "roachoids") are from the Carboniferous period 320 million years ago, as are fossil roachoid nymphs. According to one hypothesis,