Cockroaches are insects of the order Blattodea, sometimes called Blattaria, of which about 30 species out of 4,600 total are associated with human habitats. About four species are well known as pests.
Among the best-known pest species are the American cockroach, Periplaneta americana, which is about 30 mm (1.2 in) long; the German cockroach, Blattella germanica, about 15 mm (0.59 in) long; the Asian cockroach, Blattella asahinai, also about 15 mm (0.59 in) in length; and the Oriental cockroach, Blatta orientalis, about 25 mm (0.98 in). Tropical cockroaches are often much bigger, and, contrary to popular opinion, extinct cockroach relatives and 'roachoids' such as the Carboniferous Archimylacris and the Permian Apthoroblattina were not as large as the biggest modern species.
The name "cockroach" comes from the Spanish word for cockroach, cucaracha, transformed by English folk etymology into "cock" and "roach". The term cucaracha (sp. cuca "bug", and raxa "streak" (modern Spanish raya)) originally was used for the wood louse (the sow bug), but later was used to mean the palmetto bug (the flying cockroach). It is from this later Mexican usage that English-speaking Americans began using the term for regular (non-flying) cockroach.
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 moths and similar insects.
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- Blattella germanica, German cockroach
- Blaptica dubia, South American/Peruvian Dubia cockroach
- Blatta orientalis, Oriental cockroach
- Blattella asahinai, Asian cockroach
- Blaberus craniifer, true death's head cockroach
- Blaberus discoidalis, discoid cockroach or false death's head
- Eurycotis floridana, Florida woods cockroach
- Gromphadorhina portentosa, Madagascar hissing cockroach
- Laxta granicollis, bark cockroach
- Parcoblatta pennsylvanica, Pennsylvania woods cockroach
- Periplaneta americana, American cockroach
- Periplaneta australasiae, Australian cockroach
- Periplaneta brunnea, brown cockroach
- Periplaneta fuliginosa, smokybrown cockroach
- Periplaneta japonica, Japanese cockroach, a freeze-tolerant species
- Pycnoscelus surinamensis, Surinam cockroach, a greenhouse pest
- Saltoblattella montistabularis, leaproach, the only jumping cockroach
- Supella longipalpa, brown-banded cockroach
Evolutionary history and relationships
Termites were previously regarded as a separate order Isoptera to cockroaches. However recent genetic evidence strongly suggests that they evolved directly from 'true' cockroaches, and many authors now place them as an "epifamily" of Blattodea. Blattodeans (cockroaches and termites) and Mantodea (praying mantises) are closely related and are combined by entomologists into a superorder called Dictyoptera.
Historically, the name Blattaria has been used largely interchangeably with the name Blattodea, but whilst the former name was used to refer to 'true' cockroaches exclusively, the latter also includes the termites. The current catalogue of world cockroach species (the Cockroach Species File Online) uses the name Blattodea for the group. Another name, Blattoptera is also sometimes used for this group. The earliest cockroach-like fossils ("blattopterans" or "roachids") are from the Carboniferous period 354-295 million years ago, as are fossil roachoid nymphs. However, these fossils differ from modern cockroaches in having long external ovipositors and are the ancestors of mantises, as well as modern blattodeans. The first fossils of modern cockroaches with internal ovipositors appeared in the early Cretaceous.
Cockroaches live in a wide range of environments around the world. Pest species adapt readily to a variety of environments, but prefer warm conditions found within buildings. Many tropical species prefer even warmer environments.
Cockroaches are mainly nocturnal and will run away when exposed to light. A peculiar exception is the Asian cockroach, which is attracted to light.
The spines on the legs were earlier considered to be sensory, but observations of their locomotion on sand and wire meshes have demonstrated 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. These chemical trails transmit bacteria onto surfaces. 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.
Daily rhythms may also be regulated by a complex set of hormonal controls of which only a small subset have been understood. In 2005, the role of one of these proteins, pigment dispersing factor (PDF), was isolated and found to be a key mediator in the circadian rhythms of the cockroach.
Gregarious cockroaches display collective decision-making when choosing food sources. In particular, it appears that 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.
Research has shown 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. Researchers found a balance between cooperation and competition exists in the group decision-making behavior found in cockroaches. The models used in this research can also explain the group dynamics of other insects and animals.
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 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 they would be accepted by the real roaches.
Gregarious German cockroaches show different behavior when reared in isolation from when reared in a group. In one study, isolated cockroaches were less likely to leave their shelters and explore, spent less time eating, interacted less with conspecifics when exposed to them, and took longer to recognize receptive females. Because these changes occurred in many contexts, the authors suggested them as constituting a behavioral syndrome. These effects might have been due either to reduced metabolic and developmental rates in isolated individuals or the fact that the isolated individuals hadn't had a training period to learn about what others were like via their antennae.
Individual American cockroaches appear to have consistently different "personalities" regarding how they seek shelter. In addition, group personality is not simply the sum of individual choices but reflects conformity and collective decision-making.
A number of studies have explored the social structure, chemical signaling, and "social herd" characteristics of gregarious cockroaches, including German and American cockroaches. According to one review, these two model species suggest that "the social biology of domiciliary cockroaches so far can be characterised by a common shelter, overlapping generations, non-closure of groups, equal reproductive potential of group members, an absence of task specialisation, high levels of social dependence, central place foraging, social information transfer, kin recognition, and a meta-population structure [...]." One BBC article summarized these findings with the title, "Why cockroaches need their friends."
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 (3.5 in) in length and weigh more than 30 g (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. According to the Guinness World Records, the longest cockroach species is Megaloblatta longipennis, which can reach 97 mm (3.8 in) in length and 45 mm (1.8 in) across. A Central and South American species, Megaloblatta blaberoides, has the largest wingspan of up to 185 mm (7.3 in).
Cockroaches have broad, flattened bodies and relatively small heads. They are generalized insects, with few special adaptations, and may be among 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 (the tegmina) 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.
Eggs and egg capsules
Female cockroaches are sometimes seen carrying egg cases on the end of their abdomens; the egg case of the German cockroach holds about 30 to 40 long, thin eggs in a case called an ootheca. The egg capsule may take more than five hours to lay and is initially bright white in color. The eggs are hatched from the combined pressure of the hatchlings gulping air. The hatchlings are initially bright white nymphs and 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 many to claim the existence of albino cockroaches.
A female German cockroach carries an egg capsule containing around 40 eggs. She drops the capsule prior to hatching, though live births do occur in rare instances. Development from eggs to adults takes three to four months. Cockroaches live up to a year. The female may produce up to eight egg cases in a lifetime; in favorable conditions, she can produce 300 to 400 offspring. Other species of cockroaches, however, can produce an extremely high number of eggs in a lifetime; in some cases a female needs to be impregnated only once to be able to lay eggs for the rest of her life.
Some species make a hissing noise while other cockroaches (including a species in Florida) will make a chirping noise. Several Australian species practice acoustic and vibration behaviour 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 will tap the substrate in a rhythmic, repetitive manner. It is hypothesized that acoustic signals may be of greater prevalence amongst perching species, particularly those that live on low vegetation in Australia's tropics.
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 species such as 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 in the genus Cryptocercus to those in termites are such that they have been suggested 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, with the exception of Nocticola australiensise, an Australian cave-dwelling species without eyes, pigment or wings, and which recent genetic studies indicate are very primitive cockroaches.
Tracheae and breathing
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, with 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 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. 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. In one experiment, cockroaches were able to recover from being submerged underwater for half an hour. Japanese cockroach (P. 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.
Role as pests
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 are linked with allergic reactions in humans. One of the proteins that triggers allergic reactions is tropomyosin. These allergens are also linked with asthma.
General preventive measures against household pests include keeping all water and food stored away in sealed containers, using garbage cans with tight lids, 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, between kitchen cabinets, pipes, doors, and windows with some steel wool or copper mesh and some cement, putty or silicone caulk.
Control and elimination
Sodium bicarbonate (Baking Soda) kills cockroaches. Once consumed, it causes internal organs of cockroaches to burst due to gas collection.
Bay Leaves, Catnip, Mentha (Mint), Cucumber, and Garlic are all repellents to cockroaches according to Home Remedies and Tips.
Diatomaceous earth applied as a fine powder works very well to eliminate cockroaches as long as it remains in place and dry. Diatomaceous earth is harmless to humans and feels like talcum powder. Most insects, including bed bugs, are vulnerable to it.
Some 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.
Of the numerous parasites and predators of cockroaches, few have proven to be highly effective for biological control of pest species. 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 up to five minutes, 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 on it. The wasp larva feeds on the subdued living cockroach.
Bait stations, gels containing hydramethylnon or fipronil, and 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.
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 (outside the jar) leading up to the top so 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 (first century), Abu Hanifa ad-Dainuri (9th century), and Kamal al-Din al-Damiri (14th century) all offered medicines that either suggest grinding them up with oil or boiling them, and Lafcadio Hearn claimed, in the 1870s, many New Orleanians had great faith in a remedy of boiled cockroach tea.
Several cockroach species, notably Blaptica dubia, are raised as feeder insects for insectivorous pets. A few cockroach species are raised as pets, most commonly the Giant Madagascar Hissing Cockroach, Gromphadorhina portentosa.
Given its nature as an extremely resilient creature, they have been notably used for space tests. To note is Nadezhda, a cockroach sent into space by Russian scientists during Foton-M test, and became the first terrestrial creature to give birth in space.
Because of their long, persistent association with humans, cockroaches are frequently referred to in art, literature, folk tales and theater and film and real life. 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. The second part of the Harry Hole crime novels written by Jo Nesbø is called The Cockroaches (Kakerlakkene in Norwegian). In the movie Men in Black a giant alien cockroach is shown as a predator and criminal who eats a farmer and then uses his skin to disguise itself as a human being. In Oliver!, 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 postatomic bomb war universe, in which enlarged, irradiated cockroaches are present as early enemies. This is a nod to the notion of their nuclear fortitude. Also, in Franz Kafka's The Metamorphosis, a man, Gregor Samsa, is transformed overnight into a monstrous insect with cockroach-like features. He views himself as repulsive in his new identity, and is treated as a pest and burden by even his own family. Ayn Rand in her early novel "We the Living" compared the Soviet Union to a huge pile of cockroaches. During Australian Rugby League State of Origin matches, it is common slang to refer to Queensland as canetoads and New South Wales as cockroaches.
Not all depictions of cockroaches are purely negative, however. Twilight of the Cockroaches depicts the extermination of cockroaches as a holocaust, and presents a happy ending as the pregnant lead cockroach, Naomi, escapes to mother many generations. 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. Milquetoast the Cockroach was a major character in the popular comic strip Bloom County and its sequel Outland. 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. Donald Harington's satirical novel The Cockroaches of Stay More (Harcourt, 1989) imagines a community of "roosterroaches" in a mythical Ozark town where the insects are named after their human counterparts. Madonna has famously quoted, "I am a survivor. I am like a cockroach, you just can't get rid of me." This has also led to the urban legend that cockroaches are immortal. "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. The cover for Papa Roach's major label debut album Infest features a cockroach on its covers. Also, in the music video for "Between Angels and Insects", a single from the same album, cockroaches make numerous appearances, most notably in its bridge, where cockroaches come out of Jacoby Shaddix's mouth when he screams.
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