Pit-trapping antlions (Myrmeleon immaculatus, family Myrmeleontidae) have long been one of my favorite insects. My fascination is shared with fellow antlion enthusiast, Ron Wilson (Natorp's Nursery Outlet & Landscaping, Mason, OH), who has had a thriving private stock of antlions in his home landscape for years. He always lets me know when pits appear meaning the antlions are starting to roar.
The genus name Myrmeleon is derived from the Latin for ant (mymex) and lion (leon). The common name "antlion" refers to the larvae. The brown to grayish-brown, slightly hairy larvae have armor-like plating and sport impressive out-sized, sickle-shaped mandibles that are responsible for the death, destruction, and terrible fate of ants or any other small arthropods that stumble into their pits.
NOTE: You can view a short video of an antlion in action by clicking on the hotlink at the end of this Alert.
What Lies Beneath
Antlions belong to the insect order Neuroptera (neuro = nerve, ptera = wing). Adults have long, thin bodies that measure around 1" in length. They fly at night, so they’re a rare find during the day.
I don't have a picture of an adult pit-trapping antlion, but I do have pictures of an adult Spotted-Winged Antlion (Dendroleon obsoletus). Online resources claim their larvae live in "dry tree holes;" I'm not sure what that means. However, the literature notes that they are not common. Regardless, the adults have a similar body plan compared to M. immaculatus and you can see the "nerve wings" which is a feature shared with all neuropterans.
Female pit-trapping antlions insert their eggs into dry, powdery soil, or sandy soil. Favored locations include loose soil near building foundations or around the base of trees. The loose soil aids the antlion larvae in the construction of their pitfall traps. I’m also convinced building overhangs and dense tree canopies reduce flooding; these are not aquatic insects.
M. immaculatus larvae pass through 3 instar stages during their development which the literature notes may take as long as 2 years. Before pupation, the last instar larvae construct soil cocoons by using silk to glue together soil particles.
The antlion’s legs only allow them to move backward. They excavate their pitfall traps by moving backward in the loose soil in a spiral pattern and they use their mandibles like tiny shovels to flip away soil. If you pull an antlion larva from the soil, it will immediately try to cover itself with soil.
The antlions excavate a funnel-shaped pit, measuring around 3/4 - 2" wide and 1/2" deep, with the antlion buried at the bottom. Only their wicked-looking mandibles are exposed. A portent of things to come.
In 2020, I collected several antlion larvae and housed them in a 7.5-quart plastic storage container partially filled with river sand. It was an anti-ant farm.
I provisioned the antlions with ant-meat in the form of field ants (Formica sp.). My miniature menagerie allowed me to observe antlion behavior and photograph these captivating insects in action.
For example, I was surprised at how quickly the antlions constructed their conical abodes. It only took a single night for the antlions to create their pits once they were introduced to their new home.
I was also surprised by another interesting behavior that has been reported in the literature. I observed in my indoor anti-ant farm that while antlions are sit-and-wait predators, they will not sit too long. If their pitfall traps fail to capture food, the antlions move. To test this, I stopped feeding a couple of the antlions and after a few days, they moved and created new pits. The image below shows the tracks of these wandering, forlorn antlions.
Quiet on the Set … and ACTION!
When a potential prey blunders into the antlion’s pitfall trap, the loose dry soil particles provide no traction for escape. As the prey struggles, the antlion keeps thrusting its sickle-shaped mandibles in the direction of the soon-to-be meat item.
Should the prey somehow evade the gnashing mandibles and attempt to escape the pit, the antlion will make violent flicks with its head and mandibles to toss soil particles onto the sides of the pit. This creates miniature landslides that carry their hapless victim into the jaws of doom.
The antlion seizes its prey and uses its sharp-pointed mandibles to inject a toxic brew of digestive enzymes. This is no "The Princess Bride” story with Miracle Max saving a mostly dead Westley. Once the antlion’s prey is injected, recovery is inconceivable!
The antlion extracts the essence of its ill-fated prey after the digestive enzymes do their work. It then tosses the wrecked body out of the pit. You can see past meals littering the landscape around antlion pits.
Beyond their namesake prey, antlions will try to eat anything that falls into their pits of despair. For example, a few years ago, I was surprised to see that pillbugs (family Armadillidiidae) were the most prevalent prey item in a collection of antlions near my home.
These terrestrial crustaceans are heavily armored and as their common and family names imply, when threatened they roll into a pill-like ball which enhances their armored defense. Based on the number of pillbug bodies I observed around the antlion pits their heavy armor was no match for the antlion's sharp sickle-like mandibles.
Look closely in dry soil beneath the roof overhangs of structures, or around the base of large trees. If you find antlion pits, drop in a few ant snacks to see first-hand what happens.
Ant farms have long been a staple in school classrooms. However, I believe teachers could use indoor anti-ant farms to add another dimension to science in the classroom. Antlions have great edutainment value.