Crickets, family Gryllidae (also known as "true crickets"), are insects related to grasshoppers. The Gryllidae have mainly cylindrical bodies, round heads and long antennae. Behind the head is a smooth, robust pronotum. The abdomen ends in a pair of long cerci (spikes); females have a long cylindrical ovipositor. The hind legs have enlarged femora (thighs), providing power for jumping. The front wings are adapted as tough, leathery elytra (wing covers) and it is by rubbing parts of these together that some crickets chirp. The hind wings are membranous and folded when not in use for flight; many species however are flightless. The largest members of the family are the bull crickets, Brachytrupes, which are up to 5 cm (2 in) long.
There are more than 900 species of crickets; the Gryllidae are distributed all around the world except at latitudes 55 or higher, with the greatest diversity being in the tropics. They occur in varied habitats from grassland, bushes and forest to marshes, beaches and caves. Crickets are mainly nocturnal, and are best known for the loud persistent chirping song of males trying to attract females, although some species are mute. The singing species have good hearing, via the tympani (eardrums) on the tibiae of the front legs.
Crickets appear as characters in literature. The Talking Cricket features in Carlo Collodi's 1883 children's book, The Adventures of Pinocchio, and in films based on the book. The eponymous insect is central to Charles Dickens's 1845 The Cricket on the Hearth, as is the chirping insect in George Selden's 1960 The Cricket in Times Square. Crickets are celebrated in poems by William Wordsworth, John Keats, and Du Fu. They are kept as pets in countries from China to Europe, sometimes for cricket fighting. Crickets are used as food in Southeast Asia, where they are sold deep-fried in markets as snacks. They are also used to feed carnivorous pets and zoo animals. In Brazilian folklore, crickets feature as omens of various events.
Contents [hide]
1 Description
2 Distribution and habitat
3 Biology
3.1 Defence
3.2 Chirping
3.3 Flight
3.4 Diet
3.5 Reproduction and life-cycle
3.6 Inbreeding avoidance
3.7 Predators, parasites and pathogens
4 Phylogeny and taxonomy
5 In human culture
5.1 Folklore and myth
5.2 In literature
5.3 As pets and fighting animals
5.4 As food
5.5 In popular culture
6 Notes
7 References
8 Sources
9 External links
Description[edit]
African field cricket Gryllus bimaculatus
Crickets are small to medium-sized insects with mostly cylindrical, somewhat vertically flattened bodies. The head is spherical with long slender antennae arising from cone-shaped scapes (first segments) and just behind these are two large compound eyes. On the forehead are three ocelli (simple eyes). The pronotum (first thoracic segment) is trapezoidal in shape, robust and well-sclerotinized. It is smooth and has neither dorsal or lateral keels (ridges).[3]
At the tip of the abdomen is a pair of long cerci (paired appendages on rearmost segment), and in females, the ovipositor is cylindrical, long and narrow, smooth and shiny. The femora (third segments) of the back pair of legs are greatly enlarged for jumping. The tibiae (fourth segments) of the hind legs are armed with a number of moveable spurs, the arrangement of which is characteristic of each species. The tibiae of the front legs bear one or more tympani which are used for the reception of sound.[3]
The wings lie flat on the body and are very variable in size between species, being reduced in size in some crickets and missing in others. The forewings are elytra made of tough chitin, acting as a protective shield for the soft parts of the body and in males, bear the stridulatory organs for the production of sound. The hind pair are membranous, folding fan-wise under the forewings. In many species the wings are not adapted for flight.[1]
The largest members of the family are the 5 cm (2 in)-long bull crickets (Brachytrupes) which excavate burrows a metre or more deep. The tree crickets (Oecanthinae) are delicate white or pale green insects with transparent forewings while the field crickets (Gryllinae) are robust brown or black insects.[1]
Distribution and habitat[edit]
Crickets have a cosmopolitan distribution, being found in all parts of the world with the exception of cold regions at latitudes higher than about 55 North and South. They have colonised many large and small islands, sometimes flying over the sea to reach these locations, or perhaps conveyed on floating timber or by human activity. The greatest diversity occurs in tropical locations, such as in Malaysia, where 88 species were heard chirping from a single location near Kuala Lumpur. There could have been a greater number than this present because some species are mute.[1]
Crickets are found in many habitats. Members of several subfamilies are found in the upper tree canopy, in bushes and among grasses and herbs. They also occur on the ground and in caves, and some are subterranean, excavating shallow or deep burrows. Some make galleries in rotting wood, and certain beach-dwelling species can run and jump over the surface of pools.[1]
Biology[edit]
Defence[edit]
Crickets are relatively defenceless, soft-bodied insects. Most species are nocturnal and spend the day hidden in cracks, under bark, inside curling leaves, under stones or fallen logs, in leaf litter or in the cracks in the ground that develop in dry weather. Some excavate their own shallow holes in rotting wood or underground and fold in their antennae to conceal their presence. Some of these burrows are temporary shelters, used for a single day, but others serve as more permanent residences and places for mating and laying eggs. Burrowing is performed by loosening the soil with the mandibles and then carrying it with the limbs, flicking it backwards with the hind legs or pushing it with the head.[4]
Other defensive strategies are the use of camouflage, fleeing and aggression. Some species have adopted colourings, shapes and patterns that make it difficult for predators that hunt by sight to detect them. They tend to be dull shades of brown, grey and green that blend into their background, and desert species tend to be pale. Some species can fly but the mode of flight tends to be clumsy, so the most usual response to danger is to scuttle away to find a hiding place.[4]
Chirping[edit]
A male Gryllus cricket chirping. Its head faces its burrow; the leathery forewings (tegmina) are raised (clear of the more delicate hindwings) and are being scraped against each other (stridulation) to produce the song. The burrow acts as a resonator, amplifying the sound.
Most male crickets make a loud chirping sound by stridulation (a few species are mute). The stridulatory organ is located on the tegmen, or forewing, which is leathery in texture. There is a large vein running along the centre of each tegmen, with comb-like serrations on its edge forming a file-like structure, and at the rear edge of the tegmen is a scraper. The tegmina are held at an angle to the body and rhythmically raised and lowered which causes the scraper on one wing to rasp on the file on the other. In the central part of the tegmen is the "harp". This is an area of thick, sclerotinized membrane which resonates and amplifies the volume of sound, as does the pocket of air between the tegmina and the body wall. Most female crickets lack the necessary adaptations to stridulate, and these make no sound.[5]
There are several types of cricket song in the repertoire of some species. The calling song attracts females and repels other males, and is fairly loud. The courting song is used when a female cricket is near and encourages her to mate with the caller. A triumphal song is produced for a brief period after a successful mating, and may reinforce the mating bond to encourage the female to lay some eggs rather than find another male.[6] An aggressive song is triggered by contact chemoreceptors on the antennae that detect the presence of another male cricket.[7]
Crickets chirp at different rates depending on their species and the temperature of their environment. Most species chirp at higher rates the higher the temperature is (approximately 62 chirps a minute at 13 C in one common species; each species has its own rate). The relationship between temperature and the rate of chirping is known as Dolbear's Law. According to this law, counting the number of chirps produced in 14 seconds by the snowy tree cricket, common in the United States, and adding 40 will approximately equal the temperature in degrees Fahrenheit.[6]
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The calling song of a field cricket
In 1975, Dr. William H. Cade discovered that the parasitic tachinid fly Ormia ochracea is attracted to the song of the cricket, and uses it to locate the male in order to deposit her larvae on him. It was the first known example of a natural enemy that locates its host or prey using the mating signal.[8] Since then, many species of crickets have been found to be carrying the same parasitic fly, or related species. In response to this selective pressure, a mutation leaving males unable to chirp was observed amongst a population of field crickets on the Hawaiian island of Kauai, enabling these crickets to elude their parasitoid opponents.[9]
Flight[edit]
Some species such as the ground crickets (Nemobiinae) are wingless, others have small forewings and no hind wings (Copholandrevus), others lack hind wings and have shortened forewings in females only, while others are macropterous, with the hind wings longer than the forewings. In Teleogryllus, the proportion of macropterous individuals varies from very low to 100%. Probably most species with hind wings longer than forewings engage in flight.[3]
Some species like Gryllus assimilis take off, fly and land efficiently and well, while other species are clumsy fliers.[1] In some species, the hind wings are shed leaving wing stumps, usually after dispersal of the insect by flight. In other species they may be pulled off and consumed by the cricket itself or by another individual, probably providing a nutritional boost.[10]
Gryllus firmus exhibits wing polymorphism; some individuals have fully functional, long hind wings and others have short wings and cannot fly. The short-winged females have smaller flight muscles, greater ovarian development and produce more eggs, so the polymorphism adapts the cricket for either dispersal or reproduction. In some long-winged individuals, the flight muscles deteriorate during adulthood and the insect's reproductive capabilities improve.[11]
Diet[edit]
Two adult domestic crickets, Acheta domestica, feeding on carrot
Captive crickets are omnivorous: when deprived of their natural diet, they will accept a wide range of different organic foodstuffs. Some species are completely herbivorous, feeding on flowers, fruit and leaves, with ground-based species consuming seedlings, grasses, pieces of leaf and the shoots of young plants. Others are more predatory and include in their diet invertebrate eggs, larvae, pupae, moulting insects, scale insects and aphids.[12] Many are scavengers and consume various organic remains, decaying plants, seedlings and fungi.[13] In captivity, many species have been successfully reared on a diet of ground up, commercial dry dog food, supplemented with lettuce and aphids.[12]
Crickets have relatively powerful jaws, and several species have been known to bite humans.[14]
Reproduction and life-cycle[edit]
Male crickets establish their dominance over each other by aggression. They start by lashing each other with their antennae and flaring their mandibles. Unless one retreats at this stage, they resort to grappling, at the same time each emitting calls that are quite unlike those uttered in other circumstances. When one achieves dominance, it sings loudly while the loser remains silent.[15]
Females are generally attracted to males by their calls, though in non-stridulatory species, some other mechanism must be involved. After the pair have made antennal contact, there may be a courtship period during which the character of the call changes. The female mounts the male and a single spermatophore is transferred to the external genitalia of the female. Sperm flows from this into the female's oviduct over a period of a few minutes or up to an hour, depending on species. After copulation the female may remove or eat the spermatophore; males may attempt to prevent this with various ritualised behaviours. The female may mate on several occasions with different males.[16]
