There were perfect cone shaped pits in the ground as we walked on the Israel Trail in the heat of a July day, on a dirt road above the Kinneret. At first I thought that they were the imprints of hiker’s walking sticks, but it was soon clear that wasn’t the case. I thought to myself, they must be antlion pits. I’d heard of antlions (AKA doodle bugs) since childhood, but I’d never actually seen one. Don and I stopped for a few minutes to try and catch one of these insect larvae, but we weren’t successful and we walked on.
- Who made these pits?
A few weeks after that I noticed that there were similar pits around our apartment where we live in Haifa. I decided to mess around with one of these interesting creatures and made another effort to catch one – no luck. No matter what I did, whether I dug deeply under the pit and took all the substrate around the pit, and then meticulously sifted it all, I couldn’t find an antlion. What was going on here? If I dropped an ant into a pit; something would grab it, battle it, and then drag it down into the depths; so I knew an antlion was there. Why couldn’t I catch one? I spent hours on this problem, but no matter what I did, or how many of these pits I dug up, I couldn’t find the antlion which I expected. I did find tiny nondescript worms, but I wasn’t looking for a worm. I was quite frustrated to say the least.
My greatest joys in science come not when I find what I expect, but when I don’t.
It turns out that there are two kinds of creatures in the world that make the same kind of pits for the same reason. These pit builders are predators of the “sit and wait” variety. They don’t hunt for prey, instead they hide and wait for their unsuspecting victim to come to them – and then they pounce!
The first type of pit builder, the animal that I was looking for but couldn’t find, is the antlion. The most common Israeli species of antlion is called Myrmeleon hyalinus, and they are one fierce looking creature to say the least.
- Little and big antlion, Myrmeleon hyalinus
Antlions are the long lived larvae of a short lived adult which looks something like a dragonfly. Here in Israel they’ve been studied extensively in the lab of Dr. Ofer Ovadia from Ben-Gurion University of the Negev. Dr. Ovadia and his graduate student Inon Scharf have done various experiments on these animals showing that their pits depend on the substrate, the size of the antlion, the number of other antlions in the surrounding area, and on the amount of prey they have caught. You can download these papers and read more about these animals from Dr. Scharf’s webpage
But what about the second creature that makes pits? Well I should have paid more attention to the nondescript tiny worms because it was they who were making the pits and catching the ants. These worms are larvae of an insect unrelated to antlions, but instead related to mosquitoes called Vermileo sp. There is not much known about them, but I did find one paper by a scientist named Dusan Devetak from Slovenia. He showed that the wormlions constructed their pits in the finest substrate available while antlions preferred larger particle sizes. Not surprising considering that the wormlike larvae are smaller than the bug like larvae.
Perhaps you are curious as to how it could be that these unrelated animals both build the same kind of pits? It is called convergent evolution. When a trait or a behavior provides a great advantage there are many avenues to get it. For example insects, birds and bats all have wings, but they didn’t inherit their wings from a common ancestor. Instead each of their lineages evolved wings independently.
This summer if you take a walk in a sandy area, see if you can find the pits of an wormlion or an antlion and ponder the wonders of nature!
Substrate particle size-preference of wormlion Vermileo vermileo (Diptera:Vermileonidae) larvae and their interaction with antlions. by DUŠAN DEVETAK link to paper
Foraging behaviour and habitat selection in pit-building antlion larvae in constant light or dark conditions. by INON SCHARF, AZIZ SUBACH & OFER OVADIA link to paper
The effect of sand depth, feeding regime, density, and body mass on the foraging behaviour of a pit-building antlion. by Inon Scharf, Boaz Golan, and Ofer Ovadia link to paper
A trade-off between growth and starvation endurance in a pit-building antlion by Inon Scharf, Ido Filin, and Ofer Ovadia link to paper