I opened up my shop this morning, and noticed something strange. The dirt, sawdust and debris that normally filled one of the stress joints had somehow made its way up, out of the joint and was wind-rowed on the sides next to the joint. The shop had been shut up, so I knew that the wind was not responsible; the only other thing I could think of was that someone had run a small stick or wire down the joint; but no one had been in there but me.
I studied it for a minute; then I took my toe and pushed the debris back into the joint. In a few seconds, the debris flipped back out, and quite vigorously I might add. That gave me a clue; I took a small stick and ran it down the crack and sure enough, the crack was full of ant lions! They had themselves a ready made pit-fall trap for ants and other small insects. I thought this was indeed very strange; I have seen them take up residence in cracks in the sidewalk, but I've never seen anything like this. I guess you learn something every day; today was no exception.