Antlion
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[Photo] An adult antlion, camouflaged on a plank. Photo by Fir0002 http://en.wikipedia.org/wiki/User:Fir0002

Antlions are a family of insects in the order Neuroptera, classified as Myrmeleontidae (sometimes spelled as Myrmeleonidae), from the Greek "myrmex", meaning "ant", and "leo(n)", meaning "lion"; the most known genus is Myrmeleo. Strictly speaking the term antlion applies to the larval form of the members of this family. Antlions are worldwide in distribution, most common in arid and sandy habitats, and can be fairly small to very large (wingspan range of 2-15 cm). Antlions are omnivorous. The antlion larvae eat ants and other insects, while the adult antlion eats pollen and nectar.

The antlion larva is often called a "'Doodlebug"'. One theory is that it gets this name from the odd winding, spiralling trails it leaves in the sand while looking for a good location to build its trap. These trails look like someone has doodled in the sand.

The adult antlion has two pairs of long, narrow, multi-veined wings in which the apical veins enclose regular oblong spaces, and a long, slender abdomen. Although they greatly resemble dragonflies or damselflies, they belong to an entirely different order of insects. Antlions are easily distinguished from damselflies by their longer, prominent, apically clubbed antennae and different pattern of wing venation. They also are very feeble fliers and are normally found fluttering about in the night, in search of a mate. The adult is rarely seen in the wild because it is typically active only in the evening.

Development
The life cycle of the antlion begins with egg-laying or "oviposition". The female antlion repeatedly taps the sand surface with the tip of her abdomen. She then inserts her abdomen into the sand and lays an egg. The antlion larva is a ferocious-appearing creature with a robust, fusiform body bearing three pairs of walking legs and a prothorax forming a slender mobile neck for the large square head, which bears an enormous pair of sicklelike jaws (mandibles) with several sharp, hollow projections. Depending on species and where it lives, the larvae will either hide under leaves or pieces of wood, or dig pits in sandy areas.

The pupal stage of the antlion is quiescent. The larva makes a globular cocoon of sand stuck together with fine silk spun from a slender spinneret at the posterior end of the body. These cocoons may be buried several centimeters deep in the sand. It remains there for one month, until the completion of the transformation into the sexually mature insect, which then emerges from the case, leaving the pupal integument behind, and climbs to the surface. After about 20 minutes the adult's wings are fully opened and it will fly off in search of a mate. The adult is considerably larger than the larva; they exhibit the greatest disparity in size between larva and adult of any type of holometabolous insects, by virtue of the adults having an extremely thin, flimsy exoskeleton (in other words, they have extremely low mass per unit of volume). The adults are reported to subsist on plant nectar, but some species retain strong chewing jaws similar to those of the dragonfly indicating that they also feed on insects.

Pitfall construction
Having marked out the chosen site by a circular groove, the antlion larva starts to crawl backwards, using its abdomen as a plough to shovel up the soil. By the aid of one front leg it places consecutive heaps of loosened particles upon its head, then with a smart jerk throws each little pile clear of the scene of operations. Proceeding thus it gradually works its way from the circumference towards the centre. As it slowly moves round and round, the pit gradually gets deeper and deeper, until the slope angle reaches the angle of repose. When the pit is completed, the larva settles down at the bottom, buried in the soil with only the jaws projecting above the surface, often in a wide-opened position on either side of the very tip of the cone.

Trapping prey
Since the sides of the pit consist of loose sand at its angle of repose (that is, the steepest angle the sand can maintain, where it is on the verge of collapse from slight disturbance), they afford an insecure foothold to any small insects that inadvertently venture over the edge, such as ants. Slipping to the bottom, the prey is immediately seized by the lurking ant-lion; or if it attempts to scramble again up the treacherous walls of the pit, it is speedily checked in its efforts and brought down by showers of loose sand which are thrown at it from below by the larva. By throwing up loose sand from the bottom of the pit, the larva also undermines the sides of the pit, causing them to collapse and bring the prey with them. Thus it does not matter whether the larva actually strikes the prey with the sand showers.

Antlion larvae are capable of capturing and killing a variety of insects, and can even subdue small spiders. The projections in the jaws of the insect are hollow and through this the larva will suck the fluids out of its victim. After consuming the contents, the dry carcass is flicked out of the pit. The larva readies the pit once again by throwing out collapsed material from the center, steepening the pit walls to the angle of repose.

An average-sized larva digs a pit about 2 inches deep and 3 inches wide at the edge. This behavior has also evolved in a family of flies, the Vermileonidae, whose larvae dig the same sort of pit to feed on ants.

Antlions are especially abundant in soft sand beneath trees or under overhanging rocks. Apparently the larvae prefer dry places that are protected from the rain. Eventually the larva attains its maximum size and undergoes metamorphosis. The entire length of time from egg-laying to adulthood may take two or three years due to the uncertainty and irregular nature of its food supply. When it first hatches, the tiny larva specializes in very small insects, but as it grows larger, it constructs larger pits and thus catches larger prey.

In certain species of Myrmeleontidae, such as Dendroleon pantheormis, the larva, although resembling that of Myrmeleon structurally, makes no pitfall, but seizes passing prey from any nook or crevice in which it shelters.

Etymology
The exact meaning of the name ant-lion (French fourmilion) is uncertain. It has been thought that it refers to the fact that ants form a large percentage of the prey of the insect, the suffix "lion" merely suggesting destroyer or eater. Perhaps, however, the name may only signify a large terrestrial biting apterous insect, surpassing the ant in size and predatory habits.

The Japanese word for Antlion or Doodlebug is "Ari-jigoku", literally "Ant Hell". The term "ari-jigoku" is also used to describe a situation in which one has fallen into inevitable doom, and must languish while awaiting disaster.

http://en.wikipedia.org/wiki/Antlion

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