The Mantis

 

 

 

220px-praying_mantis_india1

Mantises are an order (Mantodea) of insects that contains over 2,400 species in about 430 genera in 15 families. The largest family is the Mantidae (“mantids”). Mantises are distributed worldwide in temperate and tropical habitats. They have triangular heads with bulging eyes supported on flexible necks. Their elongated bodies may or may not have wings, but all Mantodea have forelegs that are greatly enlarged and adapted for catching and gripping prey; their upright posture, while remaining stationary with fore arms folded, has led to the common name praying mantis.

The closest relatives of mantises are the termites and cockroaches (Blattodea), which are all within the superorder Dictyoptera. Mantises are sometimes confused with stick insects (Phasmatodea), other elongated insects such as grasshoppers (Orthoptera), or other insects with raptorial forelegs such as mantisflies (Mantispidae). Mantises are mostly ambush predators, but a few ground-dwelling species are found actively pursuing their prey. They normally live for about a year. In cooler climates, the adults lay eggs in autumn then die. The eggs are protected by their hard capsules and hatch in the spring. Females sometimes practice sexual cannibalism, eating their mates after copulation.

Mantises were considered to have supernatural powers by early civilizations, including Ancient Greece, Ancient Egypt, and Assyria. A cultural trope popular in cartoons imagines the female mantis as a femme fatale. Mantises are among the insects most commonly kept as pets.

Anatomy

Wing arrangement of a typical mantis, adult male Raptrix perspicua

Mantises have large, triangular heads with a beak-like snout and mandibles. They have two bulbous compound eyes, three small simple eyes, and a pair of antennae. The articulation of the neck is also remarkably flexible; some species of mantis can rotate their heads nearly 180°.[10] The mantis thorax consists of a prothorax, a mesothorax, and a metathorax. In all species apart from the genus Mantoida, the prothorax, which bears the head and forelegs, is much longer than the other two thoracic segments. The prothorax is also flexibly articulated, allowing for a wide range of movements of the head and fore limbs while the remainder of the body remains more or less immobile.[16][17]

 

The raptorial foreleg, showing the unusually long coxa, which, together with the trochanter, gives the impression of a femur. The femur itself is the proximal segment of the grasping part of the leg.

Mantises have two spiked, grasping forelegs (“raptorial legs”) in which prey items are caught and held securely. In most insect legs, including the posterior four legs of a mantis, the coxa and trochanter combine as an inconspicuous base of the leg; in the raptorial legs, however, the coxa and trochanter combine to form a segment about as long as the femur, which is a spiky part of the grasping apparatus (see illustration). Located at the base of the femur is a set of discoidal spines, usually four in number, but ranging from none to as many as five depending on the species. These spines are preceded by a number of tooth-like tubercles, which, along with a similar series of tubercles along the tibia and the apical claw near its tip, give the foreleg of the mantis its grasp on its prey. The foreleg ends in a delicate tarsus used as a walking appendage, made of four or five segments and ending in a two-toed claw with no arolium.[16][18]

Mantises can be loosely categorized as being macropterous (long-winged), brachypterous (short-winged), micropterous (vestigial-winged), or apterous (wingless). If not wingless, a mantis has two sets of wings: the outer wings, or tegmina, are usually narrow and leathery. They function as camouflage and as a shield for the hind wings, which are clearer and more delicate.[16][19] The abdomen of all mantises consists of 10 tergites, with a corresponding set of nine sternites visible in males and seven visible in females. The abdomen tends to be slimmer in males than females, but ends in a pair of cerci in both sexes.

Mantises have stereo vision.[20][21][22] They locate their prey by sight; their compound eyes contain up to 10,000 ommatidia. A small area at the front called the fovea has greater visual acuity than the rest of the eye, and can produce the high resolution necessary to examine potential prey. The peripheral ommatidia are concerned with perceiving motion; when a moving object is noticed, the head is rapidly rotated to bring the object into the visual field of the fovea. Further motions of the prey are then tracked by movements of the mantis’s head so as to keep the image centered on the fovea.[18][23] The eyes are widely spaced and laterally situated, affording a wide binocular field of vision and precise stereoscopic vision at close range.[24] The dark spot on each eye that moves as it rotates its head is a pseudopupil. This occurs because the ommatidia that are viewed “head-on” absorb the incident light, while those to the side reflect it.[25]

As their hunting relies heavily on vision, mantises are primarily diurnal. Many species, however, fly at night, and then may be attracted to artificial lights. Nocturnal flight is especially important to males in locating less-mobile females by detecting their pheromones. Flying at night exposes mantises to fewer bird predators than diurnal flight would. Many mantises also have an auditory thoracic organ that helps them avoid bats by detecting their echolocation calls and responding evasively.[26][27]

Diet and predation

Mantis eating a common bushbrown butterfly, Mycalesis perseus

Mantises are generalist predators of arthropods.[2] The majority of mantises are ambush predators that only feed upon live prey within their reach. They either camouflage themselves and remain stationary, waiting for prey to approach, or stalk their prey with slow, stealthy movements.[28] Larger mantises sometimes eat smaller individuals of their own species,[29] as well as small vertebrates such as lizards and frogs.[30]

Tenodera sinensis feeding on a cricket

Most mantises chase tempting prey if it strays close enough, and will go further when they are especially hungry.[31] Once within reach, mantises strike rapidly to grasp the prey with their spiked raptorial forelegs.[32] Some ground and bark species pursue their prey in a more active way. For example, members of a few genera such as the ground mantises, Entella, Ligaria, and Ligariella run over dry ground seeking prey, much as tiger beetles do.[16]

Ligariella, a ground mantid that runs down its prey

The fore gut of some species extends the whole length of the insect and can be used to store prey for digestion later. This may be advantageous in an insect that feeds intermittently.[33] Chinese mantises live longer, grow faster, and produce more young when they are able to eat pollen.[34]

Sexual cannibalism[edit]

Further information: Sexual cannibalism

Sexual cannibalism in Mantis religiosa

Sexual cannibalism is common among most predatory species of mantises in captivity. It has sometimes been observed in natural populations, where about a quarter of male-female encounters results in the males being eaten by the female.[47][48][49] Around 90% of the predatory species of mantises participate in sexual cannibalism.[50] Adult males typically outnumber females at first, but their numbers may be fairly equivalent later in the adult stage,[5] possibly because females selectively eat the smaller males.[51] In Tenodera sinensis, 83% of males escape cannibalism after an encounter with a female, but since multiple matings occur, the probability of a male’s being eaten increases cumulatively.[48]

The female may begin feeding by biting off the male’s head (as they do with regular prey), and if mating has 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 a ganglion in the abdomen, not the head, removal of the male’s head was a reproductive strategy by females to enhance fertilization while obtaining sustenance. Later, this behavior appeared to be an artifact of intrusive laboratory observation. Whether the behavior is natural in the field or also the result of distractions caused by the human observer remains controversial. Mantises are highly visual organisms and notice any disturbance in the laboratory or field, such as bright lights or moving scientists. Chinese mantises that had been fed ad libitum (so that they were not hungry) actually displayed elaborate courtship behavior when left undisturbed. The male engages the female in a courtship dance, to change her interest from feeding to mating.[52] Under such circumstances, the female has been known to respond with a defensive deimatic display by flashing the colored eyespots on the inside of her front legs.[53]

The reason for sexual cannibalism has been debated; experiments show that females on low quality diets have a higher chance to engage in sexual cannibalism compared to females on high quality diets.[54] Some consider that submissive males gain a selective advantage by producing offspring. This theory is supported by a quantifiable increase in the duration of copulation among males which are cannibalized, in some cases doubling both the duration and the chance of fertilization. This is contrasted by 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 that actively avoid cannibalism may mate with multiple females. The same study also found that hungry females generally attracted fewer males than those that were well fed.[55] The act of dismounting after copulation is dangerous for males, for at this time, females most frequently cannibalize their mates. An increase in mounting duration appears to indicate that males wait for an opportune time to dismount a hungry female, who would be likely to cannibalize her mate.[53]