I came across a number of these pits in a sandy area in Larose Forest the other day. They are made by antlion larvae. The larva creates the pit by burrowing backwards in the sand and then lying in wait until an unsuspecting insect falls into the pit, at which point it grabs its prey with its truly fierce looking jaws. I kept hoping I might see one of the larvae pop out, but no such luck. The adult antlions are large flying insects that look nothing like the larvae.