Antlions

Antlions: The good, the odd, the ugly

by Barb Ogg, Ph.D., UNL Extension Educator, Emeritus

In the summertime, homeowners may notice small funnel-shaped pits next to their foundations, usually in dry, fine soil. Often these pits are under the eaves or next to porches, areas that are protected from direct rainfall. Observant homeowners may also notice that as the summertime progresses, the pits become larger in diameter and more widely spaced apart. Hidden under the soil at the bottom of each pit, a predatory immature antlion waits for unsuspecting ants and other small insects to fall into the pit.

Compared with other insects, immature antlions are peculiarly adapted for constructing their pits and this predatory lifestyle. They have a broad, flattened body, short legs, (best suited for crawling backward) and a flat head with long, sickle-shaped mandibles. The larvae do not resemble the adult antlions, which look like a small damselfly and have a slender body and delicate outstretched wings.

Antlion larvae (photo right) are sometimes called doodlebugs. They get this nickname because, in the process of finding a suitable site to dig a pit, the larvae leave a narrow, irregular, twisted furrow in the soil that looks like doodling.

Antlion larvae do not seem to care about the type of soil in which they dig. Pits have been found in quartz sand, red sandstone, dust, humus, rotted wood, gypsum and coal ashes. The consistent requirement seems to be that the substrate must be composed of small, dry, loose particles. If you want to attract antlions, place sand under the eaves next to your house in an area that nearly always stays dry.

How do immature antlions move through the soil and construct their funnel-shaped pit? The shape of the larva's abdomen, with its relatively blunt anterior end gradually tapering toward the posterior enables the antlion to slide backward easily through the sand. The hairs on the antlion's body curve forward to help it move backward.

An antlion excavates its pit by using its oval-shaped abdomen as a plow and its flat head as a shovel for flicking sand upward. It circles backward through the sand and repeatedly flicks sand upward, raising its head above the soil surface. Watch an amazing video

If an antlion larva encounters a small pebble or other object when it is constructing its pit, it will attempt to flick the object out of its pit. If the object is too large to flick but large enough to move, it may literally be "pushed" up and out of the pit by the larva. When the pit is completed, the larva lies motionless on the bottom, concealed beneath the sand, with only its long, piercing mandibles exposed.

When an ant or other small insect accidentally steps inside the rim of the pit, it will slip on the soft sand particles on the side of the pit and fall to the bottom. The unfortunate victim usually becomes impaled by the antlion's piercing mandibles. But if it tries to escape, the antlion will flick sand and shower the prey. As this storm of loose sand falls on the slope of the pit, it speeds up the treadmill effect. Eventually the prey tumbles to the bottom toward the waiting antlion.

After the prey has been captured, the antlion drags the victim deeper into the sand where it sucks out its body fluids. The antlion then disposes of the carcass by flicking it out of the pit.

As the summer progresses, antlions get larger and construct a larger pit. When several antlions live near each other, they adjust the spacing between the pits so as not to interfere with each other. When the antlion larva grows to its maximum size, it changes into a pupa and then an adult, a life cycle similar to that of a butterfly. Adults mate and females lay eggs in soft, dry soil that will be suitable for their larvae.

Antlions are absolutely harmless and cause no damage to flowers, people or structures. They are highly beneficial and 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.

To learn more, visit the Antlion Pit Web site.

Photo Credits:

• Top - Soni Cochran, Nebraska Extension in Lancaster County
• Right - Betsy Matos, Iowa State University Department of Entomology. Iowa State Extension Article on Antlions

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