Cicada Killers at the Arboretum
A fascinating insect in our midst
The large wasps flying in and out of the grass along Forest Hills Road near the Bradley Rosaceous Collection every July are part of a cicada killer lek (a lek is a communal breeding site). This lek has been active for many years. In July the male cicada killer wasps (Sphecius specious) hatch out and establish territory while waiting for the larger females to dig themselves out of their burrow.
After mating, the female wasps dig foot-long burrows in the soil. See a video of a female at work!
Next, she begins to hunt for the annual dog-day cicadas (Tibicen spp.), paralyzing them with a sting. Even though cicadas are much larger than the wasps, the wasps are able to carry cicadas into their newly dug burrows. The female then lays an egg on the cicada body. The number of cicadas sealed in the burrow determines the sex of the progeny—one cicada means a male wasp will hatch, and two cicadas results in a female! After the eggs hatch the pupae feed on the paralyzed cicadas. The pupae remain underground through the winter and hatch out the following summer, completing a complex and fascinating life cycle.
Dog-day cicadas can do significant harm to trees, laying eggs under the bark of new growth, so cicada killer wasps are a beneficial insect. Although these insects look intimidating and often fly close to people, only females can sting and they do so rarely (and only if handled roughly).