Cockroach

Cockroaches (or roaches[1][2][3]) 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.

Description

Most species of cockroach are about the size of a thumbnail, but several species are larger. The world's heaviest cockroach is the Australian giant burrowing cockroach Macropanesthia rhinoceros, which can reach 8 centimetres (3 in) in length and weigh up to 35 grams (1.2 oz).[21] Comparable in size is the Central American giant cockroach Blaberus giganteus.[22] The longest cockroach species is Megaloblatta longipennis, which can reach 97 mm (3+7⁄8 in) in length and 45 mm (1+3⁄4 in) across.[23] A Central and South American species, Megaloblatta blaberoides, has the largest wingspan of up to 185 mm (7+1⁄4 in).[24] At the other end of the size scale, Attaphila cockroaches that live with leaf-cutter ants include some of the world's smallest species, growing to about 3.5 mm in length.[25]
Head of Periplaneta americana

Cockroaches are generalized insects with few special adaptations, and may be among the most primitive living Neopteran insects. They have a relatively small head and a broad, flattened body, and most species are reddish-brown to dark brown. They have large compound eyes, two ocelli, and long, flexible antennae. The mouthparts are on the underside of the head and include generalized chewing mandibles, salivary glands and various touch and taste receptors.[26]

Distribution and habitat

Cockroaches are abundant throughout the world and live in a wide range of environments, especially in the tropics and subtropics.[30] Cockroaches can withstand extremely low temperatures, allowing them to live in the Arctic. Some species are capable of surviving temperatures of −122 °C (−188 °F) by manufacturing an antifreeze made out of glycerol.[31] In North America, 50 species separated into five families are found throughout the continent.[30] 450 species are found in Australia.[32] Only about four widespread species are commonly regarded as pests.[33][34]

Cockroaches occupy a wide range of habitats. Many live in leaf litter, among the stems of matted vegetation, in rotting wood, in holes in stumps, in cavities under bark, under log piles and among debris. Some live in arid regions and have developed mechanisms to survive without access to water sources. Others are aquatic, living near the surface of water bodies, including bromeliad phytotelmata, and diving to forage for food. Most of these respire by piercing the water surface with the tip of the abdomen which acts as a snorkel, but some carry a bubble of air under their thoracic shield when they submerge. Others live in the forest canopy where they may be one of the main types of invertebrate present. Here they may hide during the day in crevices, among dead leaves, in bird and insect nests or among epiphytes, emerging at night to feed.[35]