Ant Lion, from larva to adult
I put it in a small ceramic dish filled with dry sand, and it promptly stuck its abdomen into the sand and wiggled its way underground in the time it took me to snap four pictures (about fifteen seconds).
Going . . .
Going . . .
Going . . .
And gone! Well, almost.
It then proceeded to dig a conical pit about an inch in diameter, which was surprisingly hard to photograph. I marked the rim with an oval drawn on the photo:
The pit actually shows up better in a blurry photo (taken without a flash) than in the focused one (taken with a flash).
So, anyway, I think you can see that an insect like an ant could easily miss seeing this pit, and fall in. Right into the waiting jaws of the inhabitant at the bottom.
We fed this one ant grubs from a nest of pavement ants that was living under a paver stone in our yard (the ants were raising new queens at the time, so we were able to get very fat grubs). The ant lion ate these voraciously for a few weeks, and then abruptly stopped eating. So on June 6, we carefully excavated the pit and found this spherical cocoon that looked like a ball of sand about a quarter-inch in diameter.
It stayed in the cocoon for quite a long time, finally emerging on July 2, 2012. The insect that came out was much bigger than the cocoon, well over an inch long, and it is kind of astounding that it was able to fit. It also left its pupal skin outside of the cocoon.
Unfortunately, it got itself wedged under the bowl of sand when it emerged, and its wings didn’t unfurl properly. I felt terrible about that, because if I’d put the sand bowl in a larger container, it would have been OK.
At any rate, this is definitely one of the antlions in the genus Myrmeleon, as they are the only ones that dig the conical pits as larvae. Looking at the adult, the pattern of banding on its abdomen looks like Myrmeleon immaculatus.
As it happened, a few weeks later (July 22), I found another adult ant lion that looked to be the same species, hanging out on the siding of our house.
I’m not sure what its little companion is here, it looks like some sort of bug nymph. At any rate, it looks surprised. Or maybe worshipful.
It was actually pretty unexcitable, so here it is sitting on the tip of my finger, for scale:
Eventually, it did decide to fly, landing on our doormat with its wings spread. You can see here how, when it is ready to fly, all four wings flap independently.
The best places to find antlion larvae are patches of dry sand, particularly those that are mostly protected from rain by trees or buildings. The conical pits are pretty distinctive, and to a human eye looking down from above they stick out like a sore thumb. They can be pretty numerous, too. Once when I was in Florida, I saw patches where there were dozens of ant-lion pits so close together that there was no flat sand between the pits. I kind of suspect that, in those conditions, the antlions might turn a bit cannibalistic.
 Actually, it might have done all right even with the deformed wings. I let it go on the sandy soil just inside our carriage house on July 2, and noticed on August 14 that there were about 30 new ant-lion pits within a couple of feet of where I let it go. If it was a female, then it is quite likely that a male found her and she just went ahead and laid all her eggs on the spot.