Snakeflies are a group of predatory insects comprising the order Raphidioptera, from Ancient Greek ῥαφίς (rhaphís), meaning "needle", and πτερόν (pterón), meaning "wing", with two extant families: Raphidiidae and Inocelliidae, consisting of roughly 260 species. In the past, the group had a much wider distribution than it does now; snakeflies are found in temperate regions worldwide but are absent from the tropics and the Southern Hemisphere. Recognizable representatives of the group first appeared during the Early Jurassic. They are a relict group, having reached their apex of diversity during the Cretaceous before undergoing substantial decline. An adult snakefly resembles a lacewing in appearance but has a notably elongated thorax which, together with the mobile head, gives the group their common name. The body is long and slender and the two pairs of long, membranous wings are prominently veined. Females have a large and sturdy ovipositor which is used to deposit eggs in some concealed location. They are holometabolous insects with a four-stage life cycle consisting of eggs, larvae, pupae and adults. In most species, the larvae develop under the bark of trees. They may take several years before they undergo metamorphosis, requiring a period of chilling before pupation takes place. Both adults and larvae are predators of soft-bodied arthropods.
Description
Adult snakeflies are easily distinguished from similar insects by having an elongated prothorax but not the modified forelegs of the mantis-flies. Most species are between 15 and 30 mm (0.6 and 1.2 in) in length. The head is long and flattened, and heavily sclerotised; it may be broad or taper at the back, but is very mobile. The mouthparts are strong and relatively unspecialised, being modified for biting. The large compound eyes are at the sides of the head. Members of the family Inocelliidae have no ocelli; while members of the Raphidiidae have three distinct ocelli, but are mostly differentiated by elimination, lacking the traits found in inocelliids. The prothorax is notably elongated and mobile, giving the group its common name of snakefly. The three pairs of legs are similar in size and appearance. The two pair of dragonfly-like wings are similar in size, with a primitive venation pattern, a thickened leading edge, and a coloured wingspot, the pterostigma. Inocelliids lack a cross vein in the pterostigma that is present in raphidiids. The females in both families typically have a long ovipositor, which they use to deposit their eggs into crevices or under bark.
Distribution and habitat Snakeflies are usually found in temperate coniferous forest. They are distributed widely around the globe, the majority of species occurring in Europe and Asia, but also being found in certain regions of Africa, western North America and Central America. In Africa, they are only found in the mountains north of the Sahara Desert. In North America, they are found west of the Rocky Mountains, and range from southwest Canada all the way to the Mexican-Guatemalan Border, which is the furthest south they have been found in the western hemisphere. In the eastern hemisphere, they can be found from Spain to Japan. Many species are found throughout Europe and Asia with the southern edge of their range in northern Thailand and northern India. Snakeflies have a relict distribution, having had a more widespread range and being more diverse in the past; there are more species in Central Asia than anywhere else. In the southern parts of their range, they are largely restricted to higher altitudes, up to around 3,000 m (10,000 ft). Even though this insect order is widely distributed, the range of individual species is often very limited and some species are confined to a single mountain range.
Life cycle
Snakeflies are holometabolous insects, having a four-stage life cycle with eggs, larvae, pupae and adults. Before mating, the adults engage in an elaborate courtship ritual, including a grooming behaviour involving legs and antennae. In raphidiids, mating takes place in a "dragging position", while in inocelliids, the male adopts a tandem position under the female; copulation may last for up to three hours in some inoceliid species. The eggs are oviposited into suitable locations and hatch in from a few days to about three weeks. The larvae have large heads with projecting mandibles. The head and the first segment of the thorax are sclerotised, but the rest of the body is soft and fleshy. They have three pairs of true legs, but no prolegs. However, they do possess an adhesive organ on the abdomen, which they can use to fasten themselves to vertical surfaces. There is no set number of instars the larvae will go through, some species can have as many as ten or eleven. The larval stage usually lasts for two to three years, but in some species can extend for six years. The final larval instar, the prepupal stage, creates a cell in which the insect pupates. The pupa is able to bite when disturbed, and shortly before the adult emerges, it gains the ability to walk and often leaves its cell for another location. All snakeflies require a period of cool temperatures (probably around 0 °C (32 °F)) to induce pupation. The length of the pupation stage is variable. Most species pupate in the spring or early summer, and take a few days to three weeks before ecdysis. If the larvae begin pupation in the late summer or early fall, they can take up to ten months before the adults emerge. Insects reared at constant temperatures in a laboratory may become "prothetelous", developing the compound eyes and wingpads of pupae, but living for years without completing metamorphosis.
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