Erik Draper (OSU Extension, Geauga County) shared pictures with participants in our BYGL Zoom Inservice this past week that he had received from a homeowner showing small, conical pits in the soil. The odd soil structures are the handiwork of a Pit-Trapping Antlion (Myrmeleon immaculatus, family Myrmeleontidae, order Neuroptera).
The species is native to North America and Central America, although they are most frequently found in the U.S. east of the Mississippi. As Erik informed the homeowner, the antlions are beneficial and have great potential endutainment value.
The genus and family names Myrmeleon and Myrmeleontidae are derived from the Latin for ant (mymex) and lion (leon). The common name "antlion" refers to the predatory larvae. The grayish brown, slightly hairy larvae have armor-like plating and sport impressive, outsized, sickle-shaped mandibles that are responsible for the death, destruction, and terrible fate of ants or any other small arthropod that stumbles into their pits.
Antlions belong to the insect order Neuroptera (neuro = nerve, ptera = wing), which refers to the nerve-like wing venation. Adults have long, thin bodies that measure around 1" in length. They fly at night, so they’re a rare find during the day. The image below shows a male Myrmeleon immaculatus. The specific epithet, immaculatus, is Latin for “unblemished,” or “spotless,” and references the lack of spots on the wings.
Pits of Doom and Despair
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 and building overhangs as well as dense tree canopies reduce flooding that could destroy the pits and threaten the antlions; they 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 it 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.
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 will see past meals littering the landscape around the antlion's pits of despair.
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.
Although antlions are active over the entire growing season, their excavations are less obvious when frequent rainfall continually destroys the pits, and wet soil impedes pit construction. For example, we experienced heavy rainfall over much of Ohio this spring which ruined pits and the water-logged soil delayed pit reconstruction. However, the dry conditions in August and September have allowed the antlion pits to remain apparent for extended periods.
The carnivorous antlions are part of our forest and landscape ecosystems. They are beneficial insects and cause no harm to the soil or nearby plants. Thus, their pits should be preserved and not disturbed if possible.
If you find antlion pits, drop in a few ant-snacks to see first-hand what happens. You can also see an antlion in action by viewing a YouTube video that I uploaded four years ago.
Anti-Ant Farms
Over the years, I’ve occasionally excavated antlion larvae and housed them in a 7.5-quart plastic storage container partially filled with river sand. I provisioned the antlions with ant-meat in the form of field ants (Formica sp.). The ants were easy to find, and their large size was a feast for the antlions.
The anti-ant farms allowed me to observe antlion behavior and photograph these captivating insects in action. They also helped me to educate my children on the “circle of life.” I can still hear their expressions of awe when I fed the antlions, although my wife continues to claim they sounded alarmed mixed with terrified. Oddly, neither followed in my footsteps to become an entomologist.
Regardless, the anti-ant farms were instructive. 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. While antlions are sit-and-wait predators, they will not sit too long. If their pitfall traps fail to capture food, the antlions moved their pits.
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, forsaken antlions. I’ve speculated that perhaps the antlions were aiming to enjoy an never ending buffet by intersecting a chemical trail laid down by ants to direct workers to and from a food source.
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 educational value. Of course, speaking from personal experience, teachers should avoid acting as if they're observing a Roman Colosseum spectacle when feeding the antlions.
