July Insect - Antlions: Amazingly Adapted Predators
This month, Barb Ogg, Extension Educator, tells us of an insect that provides entertainment rather than being a pest. Investigate bare soil around your acreage for signs of these beneficial predators. Read on to see that they might be more fun to watch than zombie movies!
In the summer, homeowners sometimes notice small funnel-shaped pits next to their foundations, usually in fine, dry soil or sand. A few people even call the Extension office about these pits, worried they are signs of termites — but they aren’t! The pits are often in soil directly under the eaves or next to porches — areas protected from direct rainfall. Observant individuals will notice the pits are about the same size and evenly spaced. The photo by Soni Cochran, UNL Extension, shows antlion pits with a penny for size comparisons.
At the bottom of each pit, under the soil, will be an antlion larva patiently waiting for its next lunch, an unsuspecting ant, to fall into it. The antlion larva is brownish-gray and is well camouflaged in the soil. When disturbed, the larva remains motionless, which makes it hard to find even when you know it’s there.
The antlion family, Myrmeleontidae, literally means antlion family (myrme = ant) + (leon = lion) + (idae = family). Antlions belong to the insect order Neuroptera, most of which are predators.
Antlion larvae are sometimes called doodlebugs. They get this nickname because, in the process of finding a suitable place to dig a pit, the larva leaves a narrow, irregular, twisted trail in the soil that looks like doodling. Another oddity is these larvae crawl backwards. They will be found in locations where the soil is composed of small, dry, loose particles.
The antlion larva is a ferocious-looking insect (see photo below by Barb Ogg) with a plump, spiny body and a square, flattened head with long, hollow, sickle-shaped mandibles. Like other insects, they have three pairs of legs, although you may only notice two pairs of legs from above.
The shape of the larva's abdomen, with its relatively blunt anterior end gradually tapering toward the posterior, helps the larva to slide backward easily through the sand. The hairs on the antlion's body curve forward to help it move backward. An antlion larva excavates its pit by using its flat head as a shovel, flicking sand upward. It circles backward deeper in the sand, repeatedly flicking sand until a symmetrical pit is formed.
If a larva encounters a small pebble or other object, it will try to flick the object out of its pit. If the object is too large to flick but large enough to move, the ant lion larva will push it up and out of the pit. When the pit is finished, the larva will conceal itself at the bottom, remaining motionless.
When an ant or other small insect accidentally steps inside the rim of the pit, it slips on the soft sand particles and falls to the bottom of the pit. The larva impales the ant with its sickle-shaped mandibles. But, if the ant is able to crawl up the pit, the larva will toss sand upward, causing an avalanche of loose sand to send the ant tumbling down to the bottom of the pit. After the prey has been captured, the antlion larva pulls the victim deeper into the sand and uses its hollow mandibles to sucks out its body fluids. The larva then disposes of the carcass by throwing it out of the pit.
As antlion larvae get larger, their pit gets larger and deeper. When several larvae live near each other, they adjust the spacing between the pits so they don’t interfere with each other. When the larva grows to its maximum size, it pupates by digging deeper in the soil. It pupates inside a spherical cocoon comprised of sand particles stuck together with silk. After about a month, it emerges as an adult. The adult does not resemble the larva at all, but looks similar to a small damselfly with a slender body and delicate outstretched wings. After adults mate, the adult female lays eggs in soft, dry soil.
Antlions are absolutely harmless and cause no damage to flowers, people or structures. You can handle them and they do not bite. They only feed on ants and other insects that fall into their traps. It is best to leave them alone. But, it is interesting for kids (and adults, too) to watch them make their pits and catch their prey. You can speed up the process by dropping an ant or other small insect in their pit.