Wisconsin Natural Resources magazine

Wisconsin Natural Resources magazine

Photo of antlion grasping an ant © Dwight Kuhn

An unsupecting ant slipped on the sloped sides of a conical hole, was pelted by sand grains, and then ambushed by an aggressive antlion.
© Dwight Kuhn

June 2010

A tiny terror in a sandy pit

The antlion uses engineering, dexterity and determination to ambush and attack its prey.

A barefoot stroll along a beach or over sand dunes is relaxing and the wide-open scape offers a broad view stretching to the horizon. On the other hand, if you looked down and paid attention, you just might see life and death struggles unfolding underfoot. Today, the small stuff warrants attention as well. Look closely and you might see small ants navigating the uneven "boulders" of sand grains, the "mountains" of a ripple in a dune, and a veritable redwood in a twig washed up on the shore.

I see such an ant tracing a return path across the sand weaving over and around obstacles and dangers. Small two-inch depressions pock the surface. These minor divots, little dips in the sand, soon present a surfside drama for survival. They are traps that are about to spring.

Leaning over the side of a precisely dug pit, the ant peers down, unaware. It continues into the conical depression. Steep, slippery sides are ready to avalanche sending loose sand grains tumbling with the slightest motion. Once inside there is almost no hope of escape. The ant scrambles to hold its position and slides toward the center of the cone. Suddenly a camouflaged predator springs into action from just underneath the sand. It kicks up and sprays sand, pelting the ant and mercilessly knocking it down the slope towards its waiting crushing jaws. The half-inch insect chomps onto the ant with massive pincer jaws and injects an immobilizing poison. Soon the ant's innards are liquefied and sucked out by this efficient, fierce killer that tosses the ant's spent exoskeleton out of the pit and repairs the scene for the next victim.

Be grateful these creatures are only the length of our fingernail. Antlions earn their name from their lion-like, ferocious attack and voracious appetite for ants. The predatory larva keeps this form for two years or more then develops into a four-winged insect like a damselfly or lacewing. In the Americas, another common name "doodlebug" refers to the larva's spiraling dance in the sand before it starts tracing concentric circles to mark the pit it will excavate.

Antlions reside in dry sandy areas near leaves, decaying wood particles or small rocks at the base of a tree. Wooded dunes, tree-lined river banks, and ground under piers or buildings herald great locations for their homes. In Wisconsin, antlions are active in warm months when sandy soil is unfrozen. Wisconsin has a handful of antlion species, but only one pit builder, Myrmeleon immaculatus, whose gray and brown cryptically colored body blends with the sandy soils they inhabit. Other species tend to be darker in color, a brownish gray, and either reside in wood, or live in the sand, also feeding on ants and small insects, but do not build pits and merely hide and ambush their prey.

Photo of antlion pit © Ellwin Trump
A telltale pit where an antlion lies in wait. Watch out ants!
© Ellwin Trump

In sandy areas, antlions are easy to find. Look for a small (1.5- to 3-inch) conical pit up to two inches deep, too perfect for mere coincidence. Chances are good that just under the surface, in the center of the pit, lives an antlion waiting for its next meal. You won't be the only one looking. The small pits are beacons for birds that zero-in and feed on these ferocious little lions. If you find a pit, you can coax an antlion into action. Puff some air or lightly prod the pit with a blade of grass.

Contrary to expectation, the size of the antlion does not determine the size of its pit. Hunger is the driving factor that determines the relative size of the excavation.

After spending much of their larval stage underground, antlions use woody cover as a home during metamorphosis. They create a hollow cocoon within soil or wood that keeps the antlions safe as they pupate. After one month, the adults crawl from the sand being careful not to fall into a neighbor's pit.

Adult antlions with transparent wings and brownish body resemble lacewings and are active only during the evening. In the daytime, they rest motionless trying to avoid predation. The adult phase lasts 30-40 days when the female will tap her abdomen to oviposite eggs that overwinter in soil and woody debris before emerging as snarling sand trappers that can terrorize the ant world for two to three years.