How to make a few grains of sand into a death trap
I should make it clear from the start: this piece is about the ingenious engineering approaches employed by the larvae of antlions (Myrmeleontidae) — notably ferocious predators, particularly if you happen to be an ant. If any minimalist psychopaths have clicked this headline, stop reading now.
It is well-known that antlion juveniles dig pits in sand, and hide, with only jaws showing, in wait of prey — not only ants but any small insect that happens to misadventure. It’s also known that they fling sand up the slopes of their pits with fast flicks of their head as a means of increasingly the chances of an unfortunate insect slipping to their death. Indeed, Attenborough’s covered this with typical attention to both detail and cinematography.
Antlions are maintenance experts
No-one has come at this approach to ambush predation from a mechanical angle, however — until now, that is. German scientists spent time recording the behaviour of the European antlion Euroleon nostras under lab conditions using high-speed video, and have made some discoveries beyond what was already known about the mini monster at the bottom of the pit.
Most notably, they found that in order keep pit geometry stable enough for antlion larvae not to bury themselves alive, but the angle steep enough to make prey escape unlikely, the sand ‘thrown’ is actually part of a continuous removal of that which accumulates at the centre of the pit. Call it ongoing maintenance work. After all, desperately scrambling potential prey don’t half make a mess of your construction.
Pit geometry: death or salvation
Whilst seemingly erratic, prey attempts to haul themselves back up the walls of the pit were found to be actually pretty effective at increasing the possibility of escape, altering angles in a manner conducive to their survival. But that doesn’t stop the antlion constantly striving to push things back in their favour.
They found that sand-throwing changes the average slope angle by 3.44° — a highly statistically-significant change, and one that’s going to significantly shift the chances of prey escaping for the worse. Loose packing of sand created through throwing keeps the structure teetering on the edge of instability. Through their genetically-coded actions, they are taking advantage of innate phenomena in soil mechanics.
Sand-strewn sophisticated savagery
The previous theory that sand-throwing is a means of creating sand slides that drag prey to their doom remains true; it’s just that the new findings suggest that this is only part of its function. What’s more, the researchers hypothesise that sand slides may provide information to the predator that allows it to optimise the pit’s angle.
This is not the limit of the advantages of lobbing grains with your mouthparts. It also plays a role in initial pit construction, allowing the antlion to select smaller sand grain sizes, suited to the constantly-evolving structure that in turn leads to successful predation.
Sand as construction material, sand as weapon, sand as means of communication. It does beg the question: what exactly is an antlion without its sand?
