excerpts from "Wanye's World"
|Kaweah Oaks Preserve is rich in diverse forms of animal
life, but there is one little creature that looks like something out of
a science fiction horror movie. This remarkable and long-lived creature
- 2-3 years in the larval stage, makes funnel-shaped, crater-like pits
in soft sand, and then waits patiently at the bottom to ambush a hapless
passer-by that happens to fall in. It is commonly called an antlion, referring
to its habit of preying on small crawling insects, such as ants. If antlions
were about 100 times larger, they would be a formidable threat to people.
The antlion larva is a ferocious looking creature with a robust, fusiform body bearing three pairs of walking legs and a slender neck. Its small head bears an enormous pair of sicklelike jaws (mandibles) with several sharp, teethlike projections. Like sharp hypodermic needles, the hollow jaws pierce the victim and suck fluids out of its body. According to R.E. Hutchins (Insects, 1966), the jaws are capable of injecting venom which digests and dissolves the body contents of the prey.
Antlions are members of a large order of unusual insects, the Neuroptera. They are often called the "nerve-winged insects" because of the elaborate pattern of longitudinal and cross-veins (nerves) in the four wings of adults. The order Neuroptera also includes Dobsonflies and Lacewings and is the most primitive order of insects. These insects undergo complete metamorphosis with an egg, larva, pupa and winged adult. The larval stage is typically a grotesque, wingless creature with long, sicklelike jaws. Pupation usually occurs in a silken cocoon; however, the silk is not derived from modified salivary glands as in most insects, but is produced by the Malpighian tubules and is spun from the anus! The order includes many predaceous, night-flying species, including lacewings, alderflies, snakeflies and dobsonflies. The immature or larval stage of dobsonflies, called hellgrammites, are familiar to fishermen and fisherwomen because they are commonly used as bait. One curious member of the order, called a mantispid, shows a striking resemblance to a miniature preying mantis with enlarged, grasping front legs.
Antlions belong to the Family Myrmeleontidae and include over 600 described species. Two of the most common genera in the southwestern United States are Myrmeleon and Brachynemurus. Like many other members of the order, adult antlions are commonly seen around lights and campfires, particularly during the late summer and fall. They have two pairs of long, narrow, many-veined wings and a long, slender abdomen. Although they greatly resemble small and unrelated dragonflies, called damselflies, they belong to an entirely different order of insects. The adult antlion can be readily distinguished from a damselfly by its long, clubbed antennae. It is a feeble flier and flutters about through the night air in search of a mate. As in all animals, without the mating imperative, the genes of this remarkable species would be lost forever. The most incredible part of its life cycle begins after the gravid (pregnant) female lays her eggs in the sand, and after the immature larvae hatch from the eggs.
In some species, the larva excavates a conical pit in the sand by crawling backwards in circles, at the same time flipping out sand grains with its long jaws. As it moves round and round, the pit gradually gets deeper and deeper. Eventually the crater reaches 2inches across and almost as deep, with very steep walls. The slope of the funnel is adjusted to the critical angle of repose for sand, so that the sides readily give way under the feet of a would-be escapee. The larva waits quietly at the bottom of the pit, with its body off to one side and concealed by the steep wall. Only its sicklelike jaws protrude from the sand and often they are in a wide-opened position.
When crawling insects, such as ants, inadvertently fall into the pit it is virtually impossible for them to climb the loose sand on the steep walls. To make matters worse, the antlion quickly flips out more sand, thus deepening the pit and causing miniature landslides along the walls which knock the struggling ant to the bottom. If the ant or other insect is large enough it may escape, but usually its struggle is hopeless when it is seized by the powerful jaws of the antlion. Antlion larvae are capable of capturing and killing a variety of insects, and can even subdue small spiders. Often the struggling victim is pulled beneath the sand as its body fluids are gradually siphoned out. After consuming all the contents, the lifeless, dry carcass is flicked out of the pit, and the pit is readied for a new victim.
The larvae are relatively easy to catch and maintain in captivity. Although they look ferocious, they pose no serious threat to humans. They are much too small to bite your fingers or drag you into their sand pit. When disturbed, the larva usually remains motionless. It is covered with a layer of dust or sand and is easily overlooked. All you need is a container of soft, dry sand and an ample supply of small, crawling insects for food.
Antlion cocoons resemble rabbit droppings (or M & M's® candies)
covered with sand grains. They are often buried several centimeters deep
in soft sand and are difficult to spot when you attempt to excavate them.
Right - A damselfly in its resting position. The adult antlion looks very similar, except it has a pair of long, clubbed antennae protruding from its head.
The adult antlion superficially resembles the unrelated damselfly. It can readily be distinguished by its longer, clubbed antennae and nocturnal life style.
When the cocoon is completed the larva transforms into a pupa where it remains for several weeks (or months). Finally the pupa breaks through the wall of the sand cocoon and pushes itself up to the surface. A beautiful, winged adult antlion crawls out of the pupal case and soon flutters away in search of a mate. Since they are active at night (nocturnal), it is not always that easy to find a mate in the pitch darkness of summer and fall. Luckily they are attracted to lights and their odds of meeting a mate may increase on a neon sign or window screen! It is interesting that some insects that are active during the daytime (diurnal), such as butterflies, find their mates by a phenomenon known as "hilltopping." They simply fly upslope to the summit of the nearest hill. During the summer months it is common to find dozens of species of butterflies (including beautiful tiger swallowtails) chasing each other in rather erratic flying behavior at the tops of chaparral-covered hills.
The antlion is just one of many obscure creatures living
in the southwestern United States. They are a marvelous little insect to
observe in the wild, and they make a fascinating demonstration for a sand
terrarium in the classroom. Although they live in a very competitive world,
often within disturbed, urbanized areas, they are masters of survival under
adverse conditions. If their little crater-like pitfall traps in the sand
are obliterated by the wind, rain, animals, or vehicles, they just rebuild
it and calmly wait for their next prey. In fact, it is this ingenuity and
perseverance that undoubtedly explains their survival through countless