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Crickets

 

Crickets

are insects related to grasshoppers. They 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; females have a long cylindrical ovipositor. The hind legs have enlarged femora, providing power for jumping. The front wings are tough, leathery elytra 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.Cricket 960 x 150

 

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 on the tibiae of the front legs.

Crickets are small to medium-sized insects with mostly cylindrical, somewhat vertically flattened bodies. The head is spherical with long filiform antennae arising from cone-shaped scapes and just behind these are two large compound eyes. On the forehead are three ocelli (simple eyes). The pronotum is trapezoidal in shape, robust and well-sclerotinized. It is smooth and has neither dorsal or lateral keels.

At the tip of the abdomen is a pair of long cerci, and in females, the ovipositor is cylindrical, long and narrow, smooth and shiny. The femora of the back pair of legs are greatly enlarged for jumping. The tibiae of the hind legs are armed with a number of movable 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.

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.

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.

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.

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.

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.

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.

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. Many are scavengers and consume various organic remains, decaying plants, seedlings and fungi. In captivity, many species have been successfully reared on a diet of ground up, commercial dry dog food, supplemented with lettuce and aphids.

Crickets have relatively powerful jaws, and several species have been known to bite humans.

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.

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.

Most crickets lay their eggs in the soil or inside the stems of plants, and to do this, female crickets have a long needle-like or scabre-like egg-laying organ called an ovipositor. Some ground-dwelling species have dispensed with this, either depositing their eggs in an underground chamber or pushing them into the wall of a burrow. The short-tailed cricket (Anurogryllus) excavates a burrow with chambers and a defecating area, lays its eggs in a pile on a chamber floor, and after the eggs have hatched, feeds the juveniles for about a month.

Crickets are hemimetabolic insects, whose life cycle consists of an egg stage, a larval or nymph stage that increasingly resembles the adult form as the nymph grows, and an adult stage. The egg hatches into a nymph about the size of a fruit fly. This passes through about ten larval stages, and with each successive moult it become more like an adult. After the final moult, the genitalia and wings are fully developed, but a period of maturation is needed before the cricket is ready to breed.

Crickets have many natural enemies and are subject to various pathogens and parasites. They are eaten by large numbers of vertebrate and invertebrate predators and their hard parts are often found when the contents of animal’s guts are examined. Mediterranean house geckos (Hemidactylus turcicus) have learned that although a calling decorated cricket (Gryllodes supplicans) may be safely-positioned out-of-reach in a burrow, female crickets attracted to the call can be intercepted and eaten. Crickets are simple to breed and maintain in captivity and are reared on a large scale as food for zoo and laboratory animals.

The entomopathogenic fungus Metarhizium anisopliae attacks and kills crickets and has been used as the basis of control in pest populations. The insects are also affected by the cricket paralysis virus, which has caused high levels of fatalities in cricket-rearing facilities. Other fatal diseases that have been identified in mass-rearing establishments include Rickettsia and three further viruses. The diseases may spread more rapidly if the crickets become cannibalistic and eat the corpses.[5]

Red parasitic mites sometimes attach themselves to the dorsal region of crickets and may greatly affect them. The horsehair wormParagordius varius is an internal parasite and can control the behaviour of its cricket host and cause it to enter water, where the parasite continues its lifecycle and the cricket likely drowns. The larvae of the sarcophagid fly Sarcophaga kellyi develop inside the body cavity of field crickets. Female parasitic wasps Rhopalosoma lay their eggs on crickets, and their developing larvae gradually devour their hosts. Other wasps in the family Scelionidae are egg parasitoids, seeking out batches of eggs laid by crickets in plant tissues in which to insert their eggs.

The fly Ormia ochracea has very acute hearing and targets calling male crickets. It locates its prey by ear and then lays its eggs nearby. The developing larvae burrow inside any crickets with which they come in contact and in the course of a week or so, devour what remains of the host before pupating. In Florida it was found that the parasitic flies were only present in the autumn and that at that time of year the males sang less but for longer periods. There is a trade-off for the male between attracting females and being parasitized.

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