Cicada Killers

When we last returned from WI, near the first part of August, we discovered a number of mounds of dirt in our back yard. Each mound was 8" to 10" across and very granular. Since we and our neighbors have had periodic trouble with moles over the years, we were concerned that a mole had invaded the yard and was tearing up the grass. However, we finally observed one of these mounds "in progress" and saw that a large insect was responsible for the digging. Each of the two pictures below is from a different mound in the yard, and you can see the insects at work.

These are cicada killers, large wasps that kill and utilize cicadas to propagate their species. Each cicada killer is about 2" long–they really are quite large, and at first glance they are intimidating. However, they seemed generally not to be very bothered by our presence. If we got too close, they might fly away, but they were so preoccupied, that we could get within a few feet of them to take pictures (though I did use a 135mm lens).

You can see the burrows they were creating, which were maybe 2" in diameter. They brought lots of dirt to the surface, usually pulling it out backwards. The purpose of the burrows is to lay eggs for next year's crop of cicada killers. In each case, they find and kill a cicada, fly with it or drag it back to the burrow, lay a single egg on it, and then bury it in the burrow–no more than three to a burrow and usually more like one. The egg hatches, the larva feasts on the cicada, pupates, and then rests through the winter until about this same time next year, when they hatch as full-fledged cicada killers and dig their way to the surface to start all over. Their cycles are evidently very much synchronized with the cicada populations.

Below you can see one of the cicada killers dragging a cicada to a burrow. They always seemed to carry the cicada upside down. We didn't see any flying with cicadas, but we saw several dragging cicadas, which looked like lots of work because the grass interfered with progress.

While we are not excited about the mounds of dirt in our yard (there are lots of them!), seeing the insects has been interesting, and we have been able to rake out the top of each mound to let the grass recover once the cicada killer has sealed up the burrow with its prize. We found lots more information about these insects at two web sites, which you may want to examine. Each has good pictures and interesting descriptions of their behaviors and entymology. One is at the University of Kentucky (click here), and the other is at Lafayette University (click here).