Cockroaches (or simply "roaches") are insects of the order Blattaria. The name derives from the Greek and Latin names for the insect (Doric Greek: βλάττα, blátta; Ionic and Attic Greek: βλάττη, bláttē; Latin: Blatta).
Among the best-known pest species are the American cockroach, Periplaneta americana, which is about 30 millimetres (1.2 in) long, the German cockroach, Blattella germanica, about 15 millimetres (0.59 in) long, the Asian cockroach, Blattella asahinai, also about 15 millimetres (0.59 in) in length, and the Oriental cockroach, Blatta orientalis, about 25 millimetres (0.98 in). Tropical cockroaches are often much bigger, and extinct cockroach relatives such as the Carboniferous Archimylacris and the Permian Apthoroblattina were several times as large as these.
A proposed phylogeny of the families.
Mantodea, Isoptera, and Blattaria are usually combined by entomologists into a higher group called Dictyoptera. Current evidence strongly suggests that termites have evolved directly from true cockroaches, and many authors now consider termites to be a family of cockroaches, as Blattaria excluding Isoptera is not a monophyletic group.
Historically, the name Blattaria has been used largely interchangeably with the name Blattodea, though in most recent treatments, the latter name refers to a larger grouping that includes numerous fossil groups that were related to roaches, but not true cockroaches themselves. Another name, Blattoptera has come into use for this same paraphyletic group. These earliest cockroach-like fossils ("Blattopterans" or "roachids") are from the Carboniferous period between 354–295 million years ago. However, these fossils differ from modern cockroaches in having long ovipositors and are the ancestors of mantids as well as modern cockroaches. The first fossils of modern cockroaches with internal ovipositors appear in the early Cretaceous.
Cockroaches live in a wide range of environments around the world. Pest species of cockroaches adapt readily to a variety of environments, but prefer warm conditions found within buildings. Many tropical species prefer even warmer environments and do not fare well in the average household.
The spines on the legs were earlier considered to be sensory, but observations of their locomotion on sand and wire meshes have demonstrated that they help in locomotion on difficult terrain. The structures have been used as inspiration for robotic legs.
Cockroaches leave chemical trails in their feces as well as emitting airborne pheromones for swarming and mating. Other cockroaches will follow these trails to discover sources of food and water, and also discover where other cockroaches are hiding. Thus, cockroaches can exhibit emergent behavior, in which group or swarm behavior emerges from a simple set of individual interactions.
Research has shown that group-based decision-making is responsible for complex behavior 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. Researchers found a balance between cooperation and competition exists in group decision-making behavior found in cockroaches. The models used in this research can also explain the group dynamics of other insects and animals.
Cockroaches are mainly nocturnal and will run away when exposed to light. A peculiar exception is the Asian cockroach, which is attracted to light. Another study tested the hypothesis that cockroaches use just two pieces of information to decide where to go under those conditions: how dark it is and how many other cockroaches there are. The study conducted by José Halloy and colleagues at the Free University of Brussels and other European institutions created a set of tiny robots that appear to the roaches as other roaches and can thus alter the roaches' perception of critical mass. The robots were also specially scented so that they would be accepted by the real roaches.
Additionally, researchers at Tohoku University engaged in a classical conditioning experiment with cockroaches and discovered that the insects were able to associate the scent of vanilla and peppermint with a sugar treat.
Cockroaches are rather large insects. Most species are about the size of a thumbnail, but several species are bigger. The world's largest cockroach is the Australian giant burrowing cockroach, which can reach 9 centimetres (3.5 in) in length and weigh more than 30 grams (1.1 oz). Comparable in size is the Central American giant cockroach Blaberus giganteus, which grows to a similar length but is not as heavy.
Cockroaches have a broad, flattened body and a relatively small head. They are generalized insects, with few special adaptations, and may be the most primitive living neopteran insects. The mouthparts are on the underside of the head and include generalised chewing mandibles. They have large compound eyes, two ocelli, and long, flexible, antennae.
The first pair of wings are tough and protective, lying as a shield on top of the membranous hind wings. All four wings have branching longitudinal veins, and multiple cross-veins. The legs are sturdy, with large coxae and five claws each. The abdomen has ten segments and several cerci.
Female cockroaches are sometimes seen carrying egg cases on the end of their abdomen; the egg case of the German cockroach holds about 30 to 40 long, thin eggs, packed like frankfurters in the case called an ootheca. The eggs hatch from the combined pressure of the hatchlings gulping air and are initially bright white nymphs that continue inflating themselves with air, becoming harder and darker within about four hours. Their transient white stage while hatching and later while molting has led to many claims of glimpses of an albino cockroach.
A female German cockroach carries an egg capsule containing around 40 eggs. She drops the capsule prior to hatching, though live births do rarely occur. Development from eggs to adults takes 3 to 4 months. Cockroaches live up to a year. The female may produce up to eight egg cases in a lifetime; in favorable conditions, it can produce 300 to 400 offspring. Other species of cockroach, however, can produce an extremely high number of eggs in a lifetime, but in some cases a female needs to be impregnated only once to be able to lay eggs for the rest of her life.
Aside from the famous hissing noise, some cockroaches (including a species in Florida) will make a chirping noise.
Cockroaches are most common in tropical and subtropical climates. Some species are in close association with human dwellings and widely found around garbage or in the kitchen. Cockroaches are generally omnivorous with the exception of the wood-eating genus Cryptocercus; these roaches are incapable of digesting cellulose themselves, but have symbiotic relationships with various protozoans and bacteria that digest the cellulose, allowing them to extract the nutrients. The similarity of these symbionts to those in termites are such that the genus Cryptocercus has been believed to be more closely related to termites than to other cockroaches, and current research strongly supports this hypothesis of relationships. All species studied so far carry the obligate mutualistic endosymbiont bacterium Blattabacterium cuenoti, with the exception of Nocticola australiensise, an Australian cave dwelling species without eyes, pigment or wings, and which recent genetic testing indicates could be a missing link between cockroaches and mantises.
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, 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.
Cockroaches use pheromones to attract mates, and the males practice courtship rituals such as posturing and stridulation. Like many insects, cockroaches mate facing away from each other with their genitalia in contact, and copulation can be prolonged. A few species are known to be parthenogenetic, reproducing without the need for males.
The female usually attaches the egg-case to a substrate, inserts it into a suitably protective crevice, or carries it about until just before the eggs hatch. Some species, however, are ovoviviparous, keeping the eggs inside their bodies, with or without an egg-case, until they hatch. At least one genus, Diploptera is fully viviparous.
Cockroach nymphs are generally similar to the adults, except for undeveloped wings and genitalia. Development is generally slow, and may take anything from a few months to over a year. The adults are also long-lived, and have been recorded as surviving for four years in the laboratory.
Cockroaches are among the hardiest insects on the planet. Some species are capable of remaining active for a month without food and are able to survive on limited resources like the glue from the back of postage stamps. Some can go without air for 45 minutes. In one experiment, cockroaches were able to recover from being submerged underwater for half an hour.
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 6 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.
Cockroaches are one of the most commonly noted household pest insects. They feed on human and pet food, and can leave an offensive odor. They can also passively transport microbes on their body surfaces including those that are potentially dangerous to humans, particularly in environments such as hospitals. Cockroaches have been shown to be linked with allergic reactions in humans. One of the proteins that triggers allergic reactions has been identified as tropomyosin. These allergens have also been found to be linked with asthma.
General preventive measures against household pests include keeping all food stored away in sealed containers, using garbage cans with a tight lid, frequent cleaning in the kitchen, and regular vacuuming. Any water leaks, such as dripping taps, should also be repaired. It is also helpful to seal off any entry points, such as holes around baseboards, in between kitchen cabinets, pipes, doors, and windows with some steel wool or copper mesh and some cement, putty or silicone caulk.
Cockroaches have been known to live up to three months without food and a month without water. Frequently living outdoors, although preferring warm climates and considered "cold intolerant," they are resilient enough to survive occasional freezing temperatures. This makes them difficult to eradicate once they have infested an area.
There are numerous parasites and predators of cockroaches, but few of them have proven to be highly effective for biological control. Wasps in the family Evaniidae are perhaps the most effective insect predators, as they attack the egg cases, and wasps in the family Ampulicidae are predators on adult and nymphal cockroaches (e.g., Ampulex compressa). The house centipede is probably the most effective control agent of cockroaches, though many homeowners find the centipedes themselves objectionable.
Ampulex wasps sting the roach more than once and in a specific way. The first sting is directed at nerve ganglia in the cockroach's thorax; temporarily paralyzing the victim for 2–5 minutes, which is more than enough time for the wasp to deliver a second sting. The second sting is directed into a region of the cockroach's brain that controls the escape reflex, among other things. When the cockroach has recovered from the first sting, it makes no attempt to flee. The wasp clips the antennae with its mandibles and drinks some of the hemolymph before walking backwards and dragging the roach by its clipped antennae to a burrow, where an egg will be laid upon it. The wasp larva feeds on the subdued, living cockroach.
Bait stations, gels containing hydramethylnon or fipronil, as well as boric acid powder, are toxic to cockroaches. Baits with egg killers are also quite effective at reducing the cockroach population. Additionally, pest control products containing deltamethrin or pyrethrin are very effective.
In Singapore and Malaysia, taxi drivers use Pandan leaves as a cockroach repellent in their vehicles. In Russia, some people, after opening all cupboards, leave a saucepan half-full of sulfur burning on a gas ring, then quickly come back in to switch it off (with gas mask) and leave the residence for a few days. This is said to be protective for ten years.
An inexpensive roach trap can easily be made from a deep smooth-walled jar with some roach food inside, placed with the top of the jar touching a wall or with sticks leading up to the top, so that the roaches can reach the opening. Once inside, they cannot climb back out. An inch or so of water or stale beer (by itself a roach attractant) will ensure they drown. The method works well with the American cockroach but less so with the German cockroach. A bit of Vaseline can be smeared on the inside of the jar to enhance slipperiness. The method is sometimes called the "Vegas roach trap" after it was popularized by a Las Vegas-based TV station. This version of the trap uses coffee grounds and water.
Some of the earliest writings about cockroaches encouraged their use as medicine. Pedanius Dioscorides (1st century), Kamal al-Din al-Damiri and Abu Hanifa ad-Dainuri (9th century) all offered medicines that either suggest grinding them up with oil or boiling them. The list of ailments to be treated included earaches, open wounds and "gynecological disorders."
Pest control is cited as one of the reasons for reduced populations of cockroaches in ex-USSR countries.
Because of their long, persistent association with humans, cockroaches are frequently referred to in art, literature, folk tales and theater and film. In Western culture, cockroaches are often depicted as vile and dirty pests. Their size, long antennae, shiny appearance and spiny legs make them disgusting to many humans, sometimes even to the point of phobic responses. This is borne out in many depictions of cockroaches, from political versions of the song La Cucaracha where political opponents are compared to cockroaches, through the 1982 movie Creepshow and TV shows such as the X-Files, to the Hutu extremists' reference to the Tutsi minority as cockroaches during the Rwandan Genocide in 1994 and the controversial cartoons published in the "Iran weekly magazine" in 2006 which implied a comparison between Iranian Azeris and cockroaches. In the movie Men in Black a giant alien cockroach is shown as a predator who eats a farmer and then uses his skin to disguise itself as a human being. In Oliver Twist, the children, Mr. Bumble, and Widow Corney sing about feeding Oliver cockroaches in a canister. Award-winning computer and video game series Fallout takes place in a post-nuclear war universe, in which enlarged, irradiated cockroaches are present as early enemies. This is a nod to the notion of their nuclear fortitude.
Not all depictions of cockroaches are purely negative, however. In the Pixar film Wall-E, a cockroach that has survived all humanity is the best friend of the lead character (a robot), and waits patiently on him to return. The same cockroach survives getting squished twice. In the film Joe's Apartment, the cockroaches help the titular hero, and the narrator of the book archy and mehitabel is a sympathetic cockroach. In the book Revolt of the Cockroach People, an autobiographical novel by Oscar Zeta Acosta, cockroaches are used as a metaphor for oppressed and downtrodden minorities in US society in the 1960s and 70s. The image of cockroaches as resilient also leads people to compare themselves to cockroaches. Madonna has famously quoted, "I am a survivor. I am like a cockroach, you just can't get rid of me." "Cockroach", or some variant of it is also used as a nickname, for example Boxing coach Freddie Roach, who was nicknamed La Cucaracha (The Cockroach) when he was still competing as a fighter. The album The Lonesome Crowded West by rock group Modest Mouse features a song with the title and lyric "Doin' The Cockroach". In the Netherlands 'Zaza the cockroach' becomes a buddy of the boy called Pluk in a popular Dutch book for children: 'Pluk van de Petteflet', written by Annie M.G. Schmidt. In Suzanne Collins's Underland Chronicles series, giant cockroaches are allies of humans in the Underland, and they and a toddler named Margaret (a.k.a. Boots, or "the princess," as the cockroaches call her) love each other.
Moreover, in Franz Kafka's The Metamorphosis, a man, Gregor, is transformed overnight into a dung beetle or cockroach (translation not specific, hinted at with description of beetle-or-cockroach-like features) . He views himself as repulsive in his new identity.
A Cockroach in Alcobaça, Bahia.
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Mantodea, Isoptera, and Blattaria are usually combined by entomologists into a higher group called Dictyoptera. Current evidence strongly suggests that termites have evolved directly from true cockroaches, and many authors now consider termites to be a family of cockroaches.
Historically, the name Blattaria has been used largely interchangeably with the name Blattodea. Blattodea refers to a larger group that includes fossil groups related to roaches, but not true cockroaches themselves. These earliest cockroach-like fossils ("Blattopterans" or "roachids") are from the Carboniferous period between 354–295 million years ago. However, these fossils differ from modern cockroaches in having long ovipositors and are the ancestors of mantis as well as modern cockroaches. The first fossils of modern cockroaches with internal ovipositors appear in the Lower Cretaceous. A proposed phylogeny of the families is shown in the diagram.
Cockroaches in the broader sense (Blattodea) have existed a very long time. The earliest cockroach fossils are 354–295 million years old. Science student, Cary Easterday, found a giant 300 million year old fossil cockroach 9 cm (4 in) long, in a coal mine in Ohio.
Most cockroaches are omnivores. They are physically very robust (tough), and hard to kill.
Cockroaches grow to maturity in 3-4 months and can live up to one year. A female German cockroach can produce 8 egg cases in her lifetime and each egg case may contain 30-40 eggs.
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