During our excursion to the pine barrens Andy and I found some antlion pits in the forest. We collected a few which I am now rearing on my desk but I can see why these particular larva have fascinated people for centuries with their peculiar predatory habits.
The antlion (Neuroptera: Myrmeleontidae) have been a focal point of entomologist since before the study itself was a true concept. The family name dates back to the 2nd century as the namesake of a mythical creature with the head and predatory ferocity of a lion and body of an ant. Jean-Henri Fabre himself, often considered the father of modern entomology commented on the curious nature of the antlion larva, stating,”The Ant-lion makes a slanting funnel in the sand. Its victim, the Ant, slides down the slant and is then stoned, from the bottom of the funnel, by the hunter, who turns his neck into a catapult.”(Fabre 1879). Even George Lucas used the antlion as inspiration for his famous Sarlacc pit that swallowed up anything that happened upon it or was thrown into it (RIP Boba Fett).
Much of the mystifying nature of this insect has been uncovered with time, nonetheless, it still creates great fascination. The larva of antlions is often considered the definitive form that is studied and who the name sake for the insects was granted to over the mature stage which is similar in appearance to a damselfly. The larval stage can take anywhere from 1-3 years before pupation while the adult lives only 25 days on average. The size difference between the larva and mature is the greatest of any known holometabolous insect (Swanson 2012).
The best known species of antlion are the pit digging ones but these are by no means the only ones of the 2000 known species. They are however the most fascinating in my opinion as to their ambush tactics and trap building. antlion larvae build pit-fall traps in sand similar to those made by entomologists to collect insects. These pits are roughly 1-2 inches deep and about the same in width (Fertin 2006). Passing insects such as ants but even small spiders and other arthropods would fall in similar to a man made pit fall trap. The antlion is nestled underground usually at the center of the pit lying in wait. When a disturbance is felt the antlion snaps down upon the unaware prey with its massive mandibles (Fertin 2006). A brief interlude into the mandibular morphology or the antlion larva is needed here as the form and function of these are just as fascinating as the pits set for these to be the proverbial spikes at the bottom.
The antlions mandibles are long and curved with a groove in which sit the maxillae. These create a long tube from which a paralytic venom is secreted along with enzymes that will slowly liquify the innards of its prey (Hawkeswood 2006).
Now returning to the pit in which the hapless insect has fallen into and been captured in the mandibles of the antlion. In the off chance that it escapes the mandibles of the predator and attempts to scale the walls of the pit, which is no easy task as anyone who has attempted to climb the steep side of a sand dune would know. The antlion will begin to throw sand up towards its prey causing an avalanche of sand to slowly pull the prey down once more into the pit (Fertin 2006). After the venom has worked itself in the now paralyzed prey and the enzymes have liquified the internals, The antlion through the very canals it injected the insect with will then suck up all the liquids leaving only a dried exoskeleton.
As an ambush predator in often dry sandy environments needs to be adapted to the negatives of ambushing, the largest being sometimes food won’t fall into your pit for days or even weeks. The antlion has a solution for this in its incredibly slow metabolism that allows it to go months without food (New 1991). It also is unusual in that it lacks an anus, instead holding all of its waste until maturity.
While it may seem like a ferocious, indomitable animal. Other insect species make use of its curious predatory behavior. Australian Horseflies (Diptera: Tabanidae) are known to roam around the pits much like Hyenas or Vultures waiting for the discarded corpses of the Antlions kill (Swanson 2007). More up my alley however is a parasitoid wasp of the Chalcididae family, the Lasiochalcidia igiliensis (Hymenoptera: Chalcididae) will actively attack the antlion and goad it into attacking as the venomous mandibles close around the wasp it uses its powerful hind legs to force and hold them open as it parasitizes the larva with its own eggs (Piek 2013).
This goes to show that no matter how big and scary an insect might be there is always a bigger fish (or smaller insect in this case).
Gail Hampshire says
This is a fascinating article. It is amazing the adaptations that evolve to enable parasitation in insects.