Several dirt piles pimpled a friend's Long Island lawn. It turns out that the mounds are nests burrowed by cicada killer wasps. These two-inch-long wasps look intimidating but are generally not dangerous. The males are aggressive, but stingerless while the females have large stingers but are not protective of their nests like the bees and wasps that I'm used to. The stinger's primary purpose is to paralyze cicadas to bury with a wasp egg. The cicada serves as food for the grub when it emerges from the egg in a day or two. The following picture shows the cicada killer wasp burrowing a hole in the lawn, preparing to deposit a cicada and egg into the nest.
The wasps dig impressively large dirt mounds, and fly around with cicadas twice their weight. Impressive little workers, these killers.