If you are like me, you might have thought these conical pits were a type of ant hill. Quite to the contrary, as unsuspecting ants that stumble into the pit slide to the bottom, they are quickly sucked dry of all body fluids by the antlion larva hiding just under the surface at the bottom of the pit. Iowa antlions are sit-and-wait predators, because they build the pit and wait hidden at the bottom of the pit until an ant or other prey falls.
Antlions are insects closely related to lacewings. These insects have been classified in the order Neuroptera, which literally means nerved-wings. Neuropterans are soft-bodied insects with four membranous wings which have many cross veins. These insects undergo complete metamorphosis and have an egg, larval, pupal and adult stage.
The antlion larvae over winter in Iowa and are the first stage we see at the beginning of the summer. The adults are weak fliers. They are active mostly during the night and may be attracted to porch lights and are usually present midsummer. During the day they are more difficult to find because they rest.
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In our home gardens, these important predators are found in the dry, sandy, loose soil. These sites could be near flower beds and under hedges or eaves. Antlion larvae build funnel shape pits, similar to craters on the moon, in which they catch their prey. The antlion larvae have sickle-shaped mandibles which are used to inject venom to subdue their prey. Their broad abdomen helps the antlion build its pit with a shovel and plow action.
The prey approaches the edge of the pit, and because of the sandy properties, it may slide down the pit directly on the sickle-like mandibles. The antlions inject venom and will then suck all the contents of the prey. After all the juicy contents have been sucked, the antlion discards the exoskeleton of the other insect or arthropod out of its pit.
Some entomologists say the diameter of the pit expands as the antlion grows. Antlions may become as large as a human fingernail (0.6 in) and the pits may be from 1 to 2 inches wide. Other entomologists; however, say the pit expands due to the period of time the antlion has gone without food. The bigger the pit the hungrier the antlion is, thus increasing probability of prey falling into its pit.
An antlion may continue to be a larva for up to three years before changing into a pupal form. Antlions pupate in the soil, and the cocoon is made of silk and soil. The adult may be predaceous or feed on nectar, but its real purpose is to mate and reproduce. It may live for up to a month. Females lay eggs in sandy or loose soil areas. Hopefully, the female does not go too close to where another antlion larva may have its pit, because it may become food for the owner of the pit.
Find the nearest sandy or loose soil area around your home or in a park late in the spring or early summer. Once you have located the pits built by antlions, look for prey such as ants or other small arthropods and throw it inside the pit. The antlion will do the rest. Antlions, like other animals, make important contributions to our ecosystem. Antlions are not pests. Overuse of insecticides near gardens and lawn will cause harm to antlions.
For more information on lawn and garden topics, call the Master Gardener at Iowa State University Extension, Woodbury County at (712) 276-2157 or email mimishan@iastate.edu.
