What Antlions are

Antlions, also called doodlebugs, are among the most interesting of insects. Evolution has made them remarkably adaptable, and here’s why.

So you walk by a house, and on the ground in the corner, you see a patch of sand with strange pits in them. If you don’t know what an antlion is, you may brush it off or you may conclude that tiny aliens have invaded Earth.

No, Earth is not being attacked by aliens, the pits are created by these antlion larvae. They have that name because they trap ants and various other insects into the pit they create to eat them. The insect falls into the pit, which ends into the antlion’s powerful mandibles.

Now, it’s the larvae that look like ferocious beasts. However, the adults are completely different; debatably more different than the transformation between caterpillars and butterflies. The adults are winged, have a slender body, and have rather elegant antennae.

Antlion Classification and Biology

Domain Eukaryota

Kingdom Animalia

Phylum Arthropoda Group Mandibulata Subphylum Hexapoda Class Insecta Group Pterygota Group Neoptera Group Endopterygota/ Holometabola Neuroptera Antlion (Myrmeleontidae) (EOL, Encyclopedia of Life)



Antlions are arthropods, which are animals with jointed appendages and segmentation (tagmatization). They possess mandibles, six legs, an external mouth, and thus are also insects. The antlion has a two-parted dicondylic mouth, which is also usually an indicator for wings, which the adult has. The wings can fold over the abdomen, characteristic of Neoptera. A complete metamorphosis is employed by this insects, meaning it has a larval, pupal, and adult stage. The antlion’s close relatives are lacewings, mantisflies, owlflies, and the rest of Neuroptera, the net-winged insects.

The life of an antlion, just as every insect, starts as an egg. The female adult antlion senses warm sand with her abdomen to oviposit her eggs. She will lay an egg into the soil. They are more likely to lay eggs around other antlion larvae. Because of this, adult antlions themselves may sometimes fall into an antlion larva’s pit.

The eggs will hatch into tiny antlion larvae. These larvae will form their pits. Scooting backwards, they spiral inward and down to a point that will be the center and bottom of the pit. The size of the pit depends on the time it has been since the last meal. After forming the pit, they wait patiently for a meal in the form of an ant or other insect. When an insect falls into the pit, the antlion will clamp the prey with its jaws, and drag them in. If the insect tries to escape, it will spray sand at it to slow it. The antlion has no “mouth” for ingestion. Like spiders, they will secrete an enzyme that breaks down the prey’s internal makeup, and the antlion sucks up the juices with their jaws. This means they can bite and secrete venom, however, they rarely bite, and when they do, the most it can do induce pain.

The young larvae form steeper pits than older larvae, due to a slight difference in pit construcion. The diameter of the pit formed is proportional to the length of the larva. The steepness of the young larvae ensure entrapment of prey, and reflect the need for the young larvae to avoid loss of food for quick development. In older larvae, this priority shifts, and focuses less on steepness and more on larger prey. The older larvae grow less than smaller larvae. Ants with harder exoskeletons were shown to only be attacked by the junction between the ant’s thorax and abdomen, while ants with weaker ones are attacked in other places (Griffiths, 99-125).

The antlion will continue to form pits, eat, and grow until it is ready to metamorphose. It will stop feeding and forming pits, and begin to cover itself in a spherical cocoon made of silk using a slender spinneret. Here will begin the transformation from antlion larva to adult. The adult antlion hatches out of the cocoon after about 3 weeks. It will look for a perch to sclerotize, or harden, its new body.

The adult antlion, depending on the species, could feed on either small arthropods or pollen and nectar. They are different from other similarly looking insects by the thickened antennae. Males have a longer abdomen than females. Their primary purpose is to reproduce. According to AntlionPit.com, the mating behavior is acrobatic. The female will hang upside down on a perch, and a copulating male will only be connected to her by the genital components, suspended in the air. The female will look for a site to lay eggs, completing the cycle (Engel, 1-58).

Antlion Ecology

The antlion larva is an insectivorous predator. They prey on insects susceptible to falling into their pits. The adult antlion is less strict on diet preference. They can be either entirely pollenophagous, feeding on pollen, or also predators of small insects. This means that the predatory antlion larva can potentially control the population of problematic ants. the predacious species of adult antlions could be beneficial to farmers, feeding on insect pests of crops. Pollenophagous antlions may be neutral, feeding on pollen but also aiding in pollination as pollen adheres to the insect.

The antlion larva naturally scoots backwards, in tandem with the creation of it’s trap. The abdomen functions as a shovel or bulldozer, forming a trail of sand. The antlion will revolve on the surface of the sand to form the perimeter of the pit, whose diameter is only around 5 centimeters. The antlion will drag itself deeper and gradually inwards towards the supposed center of the pit until a funnel is created, with the antlion at the bottom. The antlion waits patiently with its jaws facing the apex of the funnel, ready to strike the fallen insect.

The antlion pit relies on a number of factors. The angle at which the funnel is formed cannot be too steep to allow the pit to collapse, and it cannot be too shallow to allow the prey to escape. The angle must be in the sweet spot, the critical angle of repose. The size of substrate particles are also an important factor. Large particles have a low drag to momentum ratio, and are more prone to being thrown out of the pit. This factor deals with Stoke’s law and drag force (Lucas, 651-664).

Other insects that form pits similar to the antlion’s are fly larvae belonging to family Vermileonidae, or “wormlions”.

The antlion larva is not free of predators, or at least parasites. There exists a parasitic wasp, Lasiochalcida pubescens, that will use its strong legs to hold open the antlion’s jaws, and lays eggs on the larva. This is not the only parasitoid wasp that parasitizes antlions (Steiner, 63-148). The larvae of the Australian horsefly, Scaptia muscula, will also steal prey from antlion pits, a phenomenon known as kleptoparasitism.

There are a few antlion species that do not create these pits as well, such as Dendroleon pantherinus (Devetak et al., 159-170). They reside in the notches and cracks of trees to ambush prey.

References

DEVETAK, Duøan, Jan PODLESNIK, and Franc JANÆEKOVIŒ. “ANTLION DENDROLEON PANTHERINUS (FABRICIUS, 1787)(NEUROPTERA: MYRMELEONTIDAE) IN SLOVENIA.” Acta entomologica slovenica 18 (2010): 159 – 170.

Engel, Michael S., and David A. Grimaldi. “The neuropterid fauna of Dominican and Mexican amber (Neuropterida: Megaloptera, Neuroptera).” American Museum Novitates (2007): 1-58.

Griffiths, David. “The feeding biology of ant-lion larvae: prey capture, handling and utilization.” The Journal of Animal Ecology (1980): 99-125.

Lucas, Jeffrey R. “The biophysics of pit construction by antlion larvae (Myrmeleon, Neuroptera).” Animal Behaviour 30.3 (1982): 651-664.