“Nature will bear the closest inspection. She invites us to lay our eye level with her smallest leaf, and take an insect view of its plain.” – Henry David Thoreau
I posted a BYGL Alert last week on Jagged Ambush Bugs (Phymata spp., family Reduviidae). These diminutive bugs use flowers to attract their prey, often pollinators. They remain motionless, sometimes for hours, lying in wait for their victims. Then, as their common name implies, they spring forth to ambush their prey.
Carnivorous Pit-Trapping Antlions (Myrmeleon immaculatus, family Myrmeleontidae) don’t hunt or ambush their prey. They wait for meat items to stumble into their excavated conical pits that measure around 3/4 - 2" wide and 1/2" deep. Dry soil is key to pit construction and prey entrapment. But more on that later.
Adults are delicate insects with fine, nerve-like wing venation, which gives the order its name: Neuroptera (neuro = nerve, ptera = wing). Their long, thin bodies measure around 1" in length.
The adults fly at night, so they’re a rare find during the day. The image below shows a male M. immaculatus. The specific epithet, immaculatus, is Latin for “unblemished,” or “spotless,” and references the lack of spots on the wings.
The adults don’t look threatening, but antlion larvae look like concentrated malevolence given physical form. They are slightly hairy and have armor-like plating. Most unsettling, they sport impressive, outsized, sickle-shaped mandibles that are responsible for the death, destruction, and terrible fate of their ill-fated prey.
The antlion’s legs only allow it to move backward. They excavate their pitfall traps by moving backward in 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.
Antlion larvae place themselves in the soil off to one side at the bottom of their pits with only their mandibles exposed, positioned dead-center of the pit. As their common name indicates, ants are their favorite table fare. However, they will attack anything that is small enough for them to get their mandibles around, including pillbugs as pictured below.
Antlions tend to congregate where favorable environmental conditions support their success and long-term survival. They may take more than two years to complete their larval development, depending on food resources. Research has shown that the pits located at the edge of antlion zones are more successful in capturing prey compared to those inside the zones. Consequently, there is a constant shifting of the pits toward the edge of the antlion aggregations.
However, there is a limit. A paper published in 1993 reported that antlions had constructed pits at the base of a sandstone cliff although there were more food resources only a few meters away in a surrounding forest. The author concluded that site conditions outweigh food availability as the driving force behind pit locations.
Voracious Insecticidal Acts
Antlions are enthusiastically insecticidal. 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.
If the hapless prey somehow evades the gnashing mandibles and tries to escape, 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 luckless victim toward the jaws of doom.
Once within reach, the antlion seizes its prey with its sharp-pointed mandibles to inject a toxic brew of digestive enzymes into its doomed prey. There’s no coming back from the bite.
After the digestive enzymes do their work, the antlion extracts the essence of its lifeless prey. 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.
Several years ago, I extracted a few antlion larvae and housed them in an anti-ant farm pictured below. I provisioned the antlions with ant-meat in the form of field ants (Formica sp.). I did this to observe firsthand their brief but educational demonstrations of predator-prey dynamics.
Antlions are the result of pure predator evolution. They kill efficiently, and with style. You can observe this by watching a YouTube video that I posted a few years ago: Antlion Pit of Despair.
Digging Deeper: Antlion Populations This Season
Antlions have been with us throughout the growing season, but this is typically the time of the year when their soil pits become most obvious. However, numbers appear to be hit or miss in southwest Ohio this season.
Antlions favor locations with dry, loose soil, which is why they are commonly found near building foundations or around the base of large landscape trees. The loose soil aids the antlion larvae in their construction of pitfall traps, and the loose particles assist with prey capture. Building overhangs as well as dense landscape tree canopies reduce flooding that could destroy the pits and threaten the antlions; they are not aquatic insects.
Although we’ve had periods of droughty conditions, we’ve also had periods of heavy rainfall with localized flooding. Sites that supported antlions in the past became less conducive to their success and survival this season. On the other hand, antlion gatherings in well-protected sites have made it through our rainy summer with no apparent reduction in their numbers due to flooding.
The predatory antlions occupy various terrestrial 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.
On a final note, giant antlions would be a nightmarish addition to a sci-fi thriller appearing as a devious, malicious creature trapping hapless hikers. Of course, in reality, there’s no evidence that trekkerlions actually exist.
Selected References
Arnett, A. E., & Gotelli, N. J. (1999). Bergmann's rule in the ant lion Myrmeleon immaculatus DeGeer (Neuroptera: Myrmeleontidae): geographic variation in body size and heterozygosity. Journal of Biogeography, 26(2), 275-283.
https://www.uvm.edu/~ngotelli/manuscriptpdfs/JBiog26p275.pdf
Arnett, A. E., & Gotelli, N. J. (2001). Pit-building decisions of larval ant lions: effects of larval age, temperature, food, and population source. Journal of Insect Behavior, 14(1), 89-97.
https://www.uvm.edu/~ngotelli/manuscriptpdfs/ArnettGotelliInsectBehavior.pdf
Edmister, S. K., Williams, R. M., Varkonyi, E. M., Johnson, C. L., Ginsberg, H. S., & Alm, S. R. (2025). Ecological Observations of the Antlion, Myrmeleon immaculatus (Neuroptera: Myrmeleontidae), in Rhode Island. Northeastern Naturalist, 32(3), 407-421.
https://doi.org/10.1656/045.032.0305
Gotelli, N. J. (1993). Ant lion zones: causes of high‐density predator aggregations. Ecology, 74(1), 226-237.
https://www.uvm.edu/~ngotelli/manuscriptpdfs/Ecology74p226.pdf
Gotelli, N. J. (1996). Ant community structure: effects of predatory ant lions. Ecology, 77(2), 630-638.
https://www.uvm.edu/~ngotelli/manuscriptpdfs/Ecology77p630.pdf
Gotelli, N. J. (1997). Competition and coexistence of larval ant lions. Ecology, 78(6), 1761-1773.
https://www.uvm.edu/~ngotelli/manuscriptpdfs/Ecology78p1761.pdf
Hauber, M. E. (1999). Variation in pit size of antlion (Myrmeleon carolinus) larvae: the importance of pit construction. Physiological Entomology, 24(1), 37-40.
https://doi.org/10.1046/j.1365-3032.1999.00109.x
Heinrich, B., & Heinrich, M. J. (1984). The pit-trapping foraging strategy of the ant lion, Myrmeleon immaculatus DeGeer (Neuroptera: Myrmeleontidae). Behavioral Ecology and Sociobiology, 14(2), 151-160.
https://doi.org/10.1007/BF00291906
Linton, M. C., Crowley, P. H., Williams, J. T., Dillon, P. M., Aral, H., Strohmeier, K. L., & Wood, C. (1991). Pit relocation by antlion larvae: a simple model and laboratory test. Evolutionary Ecology, 5(2), 93-104.
https://doi.org/10.1007/BF02270826
Scharf, I., & Ovadia, O. (2006). Factors Influencing Site Abandonment and Site Selection in a Sit-and-Wait Predator: A Review of Pit-Building Antlion Larvae. Journal of Insect Behavior, 19(2), 197-218.
https://doi.org/10.1007/s10905-006-9017-4
