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Mantis

[man-tis]

The insect order Mantodea or mantises consists of approximately 2,000 species worldwide in temperate and tropical habitats, of which a majority are in the family Mantidae. For most of the past century, only this single family was recognized within the order, and the term "mantid" was therefore historically used for any member of the order; technically, however, the term only refers to this one family, meaning the species in the other eight recently-established families are not mantids, by definition (i.e., they are empusids, or hymenopodids, etc.), and the term "mantises" (or the more colloquial "praying mantises") should be used when referring to the entire order. Often mistakenly spelled preying mantis (an eggcorn, since they are notoriously predatory), they are in fact named for the typical "prayer-like" stance. The word mantis derives from the Greek word mantis for prophet or fortune teller. In Europe, the name "praying mantis" refers to only a single species, Mantis religiosa. The closest relatives of mantises are the orders Isoptera (termites) and Blattodea (cockroaches), and these three groups together are sometimes ranked as an order rather than a superorder.

Description

Mantises are exclusively predatory and their diet usually consists of living insects; larger species have been known to prey on small lizards, frogs, birds, snakes, and even rodents. Most mantises are ambush predators, waiting for prey to stray too near. The mantis then lashes out at remarkable speed. Some ground and bark species, however, pursue their prey rather quickly. Prey are caught and held securely with grasping, spiked forelegs ("raptorial legs"); the first thoracic segment, the prothorax, is commonly elongated and flexibly articulated, allowing for greater range of movement of the front limbs while the remainder of the body remains more or less immobile. The articulation of the head is also remarkably flexible, permitting nearly 300 degrees of movement in some species, allowing for a great range of vision (their compound eyes have a large binocular field of vision) without having to move the remainder of the body. As their hunting relies heavily on vision, they are primarily diurnal, but many species will fly at night, and can be commonly encountered at lights.

Camouflage

Mantises are masters of camouflage and most species make use of protective coloration to blend in with the foliage or substrate, both to avoid predators themselves, and to better snare their victims. Various species have adapted to not only blend with the foliage, but to mimic it, appearing as either living or withered leaves, sticks, tree bark, blades of grass, flowers, or even stones. Some species in Africa and Australia are able to turn black after a molt following a fire in the region to blend in with the fire ravaged landscape (fire melanism). While mantises can bite, they have no venom, and are not dangerous to humans. They do not appear to be chemically protected; nearly any large predatory animal will eat a mantis if it is able to detect it (mantises are generally quite aggressive towards one another, in fact, and most species are readily cannibalistic when given the opportunity).

Evolution

Mantises are evolved from proto-cockroaches, diverging from their common ancestors by the Cretaceous period, possibly from species like Raphidiomimula burmitica, a predatory cockroach with mantis-like forelegs. Possibly the earliest known modern mantis is Regiata scutra, although more common (and confirmed) is Santanmantis, a stilt-legged genus, also from the Cretaceous. Like their close termite cousins, though, mantises did not become common and diverse until the early Tertiary period.

Reproduction and life history

Sexual cannibalism is common among mantises in captivity, and under some circumstances may also be observed in the field. The female may start feeding by biting off the male’s head (as with any prey), and if mating had begun, the male’s movements may become even more vigorous in its delivery of sperm. Early researchers thought that because copulatory movement is controlled by ganglion in the abdomen, not the head, removal of the male’s head was a reproductive strategy by females to enhance fertilisation while obtaining sustenance. Later, this bizarre behaviour appeared to be an artifact of intrusive laboratory observation. Whether the behaviour in the field is natural, or also the result of distractions caused by the human observer, remains controversial. Mantises are highly visual creatures, and notice any disturbance occurring in the laboratory or field such as bright lights or moving scientists. Research by Liske and Davis (1987) and others found (e.g. using video recorders in vacant rooms) that Chinese mantises that had been fed ad libitum (so were not starving) actually displayed elaborate courtship behavior when left undisturbed. The male engages the female in courtship dance, to change her interest from feeding to mating. Courtship display has also been observed in other species, but it does not hold for all mantises.

The reason for sexual cannibalism has been the subject of some debate, with some considering submissive males to be achieving a selective advantage in their ability to produce offspring. This theory is supported by a quantifiable increase in the duration of copulation among males who are cannibalized, in some cases doubling both the duration and the chance of fertilization. This is further supported in a study where males were seen to approach hungry females with more caution, and were shown to remain mounted on hungry females for a longer time, indicating that males actively avoiding cannibalism may mate with multiple females. The act of dismounting is one of the most dangerous times for males during copulation, for it is at this time that females most frequently cannibalize their mates. This increase in mounting duration was thought to indicate that males would be more prone to wait for an opportune time to dismount from a hungry female rather than from a satiated female that would be less likely to cannibalize its mate. Some consider this to be an indication that male submissiveness does not inherently increase male reproductive success, rather that more fit males are likely to approach a female with caution and escape.

The mating season in temperate countries typically begins in autumn. To mate following courtship, the male usually leaps onto the female’s back, and clasps her thorax and wing bases with his forelegs. He then arches his abdomen to deposit and store sperm in a special chamber near the tip of the female’s abdomen.

Depending on the species, the female then lays between 10 to 400 eggs. These are typically deposited in a frothy mass that is produced by glands in the abdomen. This froth then hardens, creating a protective capsule with a further protective coat, and the egg mass is called an ootheca. Depending on the species these can be attached to a flat surface, wrapped around a plant or even deposited in the ground. In spite of the versatility and durability of the eggs, they are often preyed on, especially by several species of parasitic wasps. In a few species, the mother guards the eggs.

As in related insect groups, mantises go through three stages of metamorphosis: egg, nymph, and adult (mantises are among the hemimetabolic insects). The nymph and adult insect are structurally quite similar, except that the nymph is smaller and has no wings or functional genitalia. The nymphs are also sometimes colored differently from the adult, and the early stages are often mimics of ants. A mantis nymph increases in size (often changing its diet as it does so) by replacing its outer body covering with a sturdy, flexible exoskeleton and molting when needed. This can happen up to five to ten times, depending on the species. After the final molt most species have wings, though some species are wingless or brachypterous ("short-winged"), particularly in the female sex.

In tropical species, the natural lifespan of a mantis in the wild is about 10-12 months, but some species kept in captivity have been sustained for 14 months. In colder areas, females will die during the winter (as well as any surviving males).

Behavior

Generally, mantises are protected simply by virtue of concealment. When directly threatened, many mantis species stand tall and spread their forelegs, with their wings fanning out wide. The fanning of the wings evidently makes the mantis seem larger and more threatening, with some species having bright colors and patterns on their hind wings and inner surfaces of their front legs for this purpose. If harassment persists, a mantis may then strike with its forelegs and attempt to pinch or bite. As part of the threat display, some species also may produce a hissing sound by expelling air from the abdominal spiracles. When flying at night, at least some mantises are able to detect the echolocation sounds produced by bats, and when the frequency begins to increase rapidly, indicating an approaching bat, they will stop flying horizontally and begin a descending spiral toward the safety of the ground, often preceded by an aerial loop or spin.

Mantises, like stick insects, show rocking behaviour in which the insect makes rhythmic, repetitive side-to-side movements. Functions proposed for this behaviour include the enhancement of crypsis by means of the resemblance to vegetation moving in the wind. However the repetitive swaying movements may be most important in allowing the insects to discriminate objects from the background by their relative movement, a visual mechanism typical of simpler animals. Rocking movements by these generally sedentary insects may replace flying or running as a source of relative motion of objects in the visual field.

Pest control uses

Many gardeners consider mantises to be desirable insects, as they prey upon many harmful insect species. Organic gardeners who avoid pesticides may encourage mantises as a form of biological pest control. Tens of thousands of mantis egg cases are sold each year in some garden stores for this purpose.

However, mantises prey on neutral and beneficial insects as well, basically eating anything they can successfully capture and devour. Although their diet primarily consists of small invertebrates, large mantises have been observed eating small vertebrates such as lizards, mice, snakes, and small birds such as hummingbirds.

Conservation status

Only one Spanish species, Apteromantis aptera, is listed as Lower Risk/Near Threatened. With one exception (the ground mantis Litaneutria minor in Canada, where it is rare - though it is common in the United States), North American mantises are not included among threatened or endangered species, though species in other parts of the world are under threat from habitat destruction. The European mantis (Mantis religiosa) is the state insect of Connecticut, but the General Statutes of Connecticut do not list any special protected status, as it is a non-native species from Europe and Northern Africa.

Introduced species

About 20 species are native to the United States, including the common Carolina mantis, and only one in Canada. Two species (the Chinese mantis and the European Mantis) were deliberately introduced to serve as pest control for agriculture, and have spread widely in both countries. While it is legal to keep native mantises as pets or to sell egg cases for gardening, non-native species are illegal to possess and release in the United States, under the Non Native Invasive Species Act of 1992.

Historical references

One of the earliest mantis references is in the ancient Chinese dictionary Erya, which gives its attributes in poetry (representing courage and fearlessness), as well as a brief description. A later text, the Jingshi Zhenglei Daguan Bencao 經史證類大觀本草 ("Bencao of the Daguan period, Annotated and Arranged by Types, Based upon the Classics and Historical Works") from 1108, is impressively correct on the construction of the egg packages, the development cycle, the anatomy and even the function of the antennae.

Western descriptions of the biology and morphology of the mantises had become relatively accurate by the 18th century. Roesel von Rosenhof accurately illustrated and described them in the Insekten-Belustigungen (Insect Entertainments). Aldous Huxley made philosophical observations about the nature of death while two mantises mated in the sight of two characters in the novel Island (the species was Gongylus gongylodes). The naturalist Gerald Durrell's autobiography My Family and Other Animals includes an account of a very evenly matched battle between a mantis and a gecko.