COCKROACH ( Blattodea )

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Phylum Arthropoda

Subphylum Hexapoda

Class Insecta

Subclass Pterygota

Infraclass Neoptera

Superorder Dictyoptera

Order Blattodea




Cockroaches are insects of the order Blattodea, which also includes termites. About 30 cockroach species out of 4,600 are associated with human habitats. About four species are well known as pests. The cockroaches are an ancient group, dating back at least as far as the Carboniferous period, some 320 million years ago. Those early ancestors however lacked the internal ovipositors of modern roaches. Cockroaches are somewhat generalized insects without special adaptations like the sucking mouthparts of Hemiptera; they have chewing mouthparts and are likely among the most primitive of living neopteran insects. They are common and hardy insects, and can tolerate a wide range of environments from Arctic cold to tropical heat. Tropical cockroaches are often much bigger than temperate species, and, contrary to popular belief, extinct cockroach relatives and roachoids such as the Carboniferous Archimylacris and the Permian Apthoroblattina were not as large as the biggest modern species. 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, though the great majority of species are inoffensive and live in a wide range of habitats around the world.


Most species of cockroach are about the size of a thumbnail, but several species are bigger. The world's heaviest cockroach is the Australian giant burrowing cockroach Macropanesthia rhinoceros, which can reach 9 cm in length and weigh more than 30 g .Comparable in size is the Central American giant cockroach Blaberus giganteus, which grows to a similar length. The longest cockroach species is Megaloblatta longipennis, which can reach 97 mm in length and 45 mm across. A Central and South American species, Megaloblatta blaberoides, has the largest wingspan of up to 185 mm .

Distribution and habitat

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

Collective decision-making

Gregarious cockroaches display collective decision-making when choosing food sources. When a sufficient number of individuals (a quorum) exploits a food source, this signals to newcomer cockroaches that they should stay there longer rather than leave for elsewhere. Other mathematical models have been developed to explain aggregation dynamics and conspecific recognition. Group-based decision-making is responsible for complex behaviors such as resource allocation. In a study where 50 cockroaches were placed in a dish with three shelters with a capacity for 40 insects in each, the insects arranged themselves in two shelters with 25 insects in each, leaving the third shelter empty. When the capacity of the shelters was increased to more than 50 insects per shelter, all of the cockroaches arranged themselves in one shelter. Cooperation and competition are balanced in cockroach group decision-making behavior. Cockroaches appear to use just two pieces of information to decide where to go, namely how dark it is and how many other cockroaches there are. A study used specially-scented roach-sized robots that appear to the roaches as real to demonstrate that once there are enough insects in a place to form a critical mass, the roaches accepted the collective decision on where to hide, even if this was an unusually light place.


Some species make a hissing noise while other cockroaches make a chirping noise. The Madagascar hissing cockroach produces its sound through the modified spiracles on the fourth abdominal segment. Several different hisses are produced, including disturbance sounds, produced by adults and larger nymphs, and aggressive, courtship and copulatory sounds produced by adult males. Henschoutedenia epilamproides has a stridulatory organ between its thorax and abdomen, but the purpose of the sound produced is unclear. Several Australian species practice acoustic and vibration behavior as an aspect of courtship. They have been observed producing hisses and whistles from air forced through the spiracles. Furthermore, in the presence of a potential mate, some cockroaches tap the substrate in a rhythmic, repetitive manner. Acoustic signals may be of greater prevalence amongst perching species, particularly those that live on low vegetation in Australia's tropics.


Cockroaches are among the hardiest insects. Some species are capable of remaining active for a month without food and are able to survive on limited resources, such as the glue from the back of postage stamps. Some can go without air for 45 minutes. Japanese cockroach (Periplaneta japonica) nymphs, which hibernate in cold winters, survived twelve hours at ?5 °C to ?8 °C in laboratory experiments. Experiments on decapitated specimens of several species of cockroach found a variety of behavioral functionality remained, including shock avoidance and escape behavior, although many insects other than cockroaches are also able to survive decapitation, and popular claims of the longevity of headless cockroaches do not appear to be based on published research. The severed head is able to survive and wave its antennae for several hours, or longer when refrigerated and given nutrients. It is popularly suggested that cockroaches will "inherit the earth" if humanity destroys itself in a nuclear war. Cockroaches do indeed have a much higher radiation resistance than vertebrates, with the lethal dose perhaps six to 15 times that for humans. However, they are not exceptionally radiation-resistant compared to other insects, such as the fruit fly. The cockroach's ability to withstand radiation better than human beings can be explained through the cell cycle. Cells are most vulnerable to the effects of radiation when they are dividing. A cockroach's cells divide only once each time it molts, which is weekly at most in a juvenile roach. Since not all cockroaches would be molting at the same time, many would be unaffected by an acute burst of radiation, but lingering radioactive fallout would still be harmful.