These creatures doodle in the sand as larvae until suitable sand is found. Tracks of their passage remind of miniature gopher or mole tunnels. They feed on small insects that slide down the sand of their pits for several seasons until enough food kicks off a metamorphosis. The larvae then transforms into a lacewing. How cool is that? I remember being fascinated by the pits as a child, when I saw dozens in the sand under a jungle gym. I was just noticing all the tiny anthills when these pits surprised me.
I seem to have a renewed love of nature this Spring since I am spending so much time walking. I almost took a picture of a robin pulling a dried worm off a curb, tugging and peeling up the length of worm jerky left stranded when the storm water evaporated. Yep, I am that goofy.
This article in Wikipedia is well written.