Crickets (order Orthoptera, family Grillidae) are found throughout the world except for the polar regions. More than 900 species have been described. Often heard, but more seldom seen, at first glance crickets are quite similar to grasshoppers and bush crickets—also known as long-horned grasshoppers or katydids—but may be distinguished from these insects by their much longer, thread-like antennae. Crickets can also be easily identified by long hindlegs used for jumping. Most species are black or brown in appearance, which helps to conceal them and therefore reduce the risk of detection from predatory small mammals and birds.
A cricket's body is divided into three sections: the head, which bears the large eyes, antennae, and mouth-parts; the thorax, which is separated into three segments (each of which bears one pair of segmented legs and efficient claws) and supports the wings; and the abdomen. There are typically two pairs of wings, of which the front pair are thicker. At rest, the wings are held flat over the insect's back with the edges bent down along the sides of the body. Some species, however, may just have one pair of wings, while others still have lost all power of flight. Among the latter are some of the smallest members of the Orthoptera, the ant-loving crickets that measure less than an inch (3–5mm) and live in underground ant nests. Despite the presence of wings on some species, none of the crickets are exceptionally good fliers; most rely on a combination of short flights and jumps to move to new feeding patches.
Crickets are active during the day and night, depending on the species; some prefer the warmth of full sunlight, others prefer the twilight hours of dusk, while quite a few species are only active at nighttime. Most species live in open grassland or woodlands, but others such as the mole crickets (family Gryllotalpidae) spend much time underground, only emerging occasionally to fly from one site to another. Mole crickets are easily distinguished from all other insects by their broad, spade-like front legs which have evolved as powerful digging tools. Armed with these and strong blade-like teeth, the mole cricket is well equipped to dig shallow tunnels in moist soils.
Crickets are versatile insects and are capable of feeding off a wide range of organisms. Largely vegetarian, they eat a great variety of young leaves, shoots, and stems but may also eat other insects (adults and larvae), as well as a range of dead or decaying matter, including household wastes. Like other orthopterans such as grasshoppers and locusts, their mouthparts are designed for biting and chewing.
Sound is important to all orthopterans, and crickets have specialized hearing organs (called tympanum) on their front legs, by which they are able to detect vibrations. Living in dense forests or rugged, tall grasslands can pose certain problems for small insects when it comes to finding a suitable mate. Crickets have solved this problem through an elaborate system of singing, which advertises their presence. Only male crickets are able to "sing" by a process known as stridulation. When he is ready to perform, the male chooses his auditorium carefully and, with both wings held above the body, begins to slowly rub one against the other. The right forewing bears a special adaptation which has been described as a toothed rib, or file; when this is rubbed against the hind margin of the left forewing, it produces a musical sound. In order to avoid confusion between different species, each cricket has its own distinct song, which varies not only in duration, but also in pitch. Among the songs commonly used are those used to attract females from a wide area around the male, while others serve as a courtship song once the amorous male has succeeded in gaining the interest of a passing female.
As the courtship ritual proceeds—either within a short burrow or amongst vegetation—the male deposits a number of small capsules (spermatophores) containing sperm cells. These are then collected by the female and used to fertilize her eggs. Female crickets lay their eggs singly in the ground and in plant tissues, sometimes using their long, needle-like ovipositors, specialized egglaying organs, to make an incision in the plant stem. When the eggs hatch, a small nymph-like replica of the adult cricket emerges and immediately begins to feed. As the nymphs grow, they molt, casting off their outer skeleton, perhaps as many as 10 times before they finally reach adult size. Depending on when the eggs were laid, the young nymphs or eggs themselves may have to spend the winter in a dormant state underground, emerging the following spring and summer to develop and breed.
Among the exceptions to this general pattern of reproduction is the parental nature of the mole crickets. Females may lay up to 300 eggs in an underground nest where, unlike most other insects, she guards them from potential predators and remains with the young nymphs for several weeks after they hatch, sometimes until just before they begin to disperse. As with other crickets, these nymphs then pass through many stages of growth and do not reach full adult size until the year after hatching.
Although widely conceived as major crop pests, most crickets are thought to cause relatively little harm. Some species, such as the house cricket (Acheta domestica) which has unwittingly been transported all around the world by humans, are considered a pest and health hazard because of their liking for garbage heaps. In contrast, mole crickets are now being increasingly viewed as beneficial to many horticulturalists as they feed on a wide range of soil-dwelling larvae that cause considerable damage to crops. They, and other grassland species, have, however, suffered heavily through hanging agricultural practices, as well as the increased and often excessive use of pesticides and inorganic fertilizer which reduces the natural diversity of other insects (many of which are eaten by crickets) and plants in agricultural areas.
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