Annual Dog-Day Cicadas (Tibicen spp.; family Cicadidae) are singing throughout much of Ohio. Normally this means their nemesis, Cicada Killer Wasps (Sphecius speciosus), would be seen cruising woodlands and landscapes in search of their exclusive prey. However, I have yet to see a wasp. Could wet spring soil conditions have reduced their numbers?
Annual dog-day cicadas share several behavioral traits with periodical cicadas (Magicicada spp.; family Cicadidae). The nymphs of both types of cicadas develop underground sustained by juices sucked from tree roots and it takes multiple years for them to complete their development from eggs to new adults.
Periodical cicadas are so-named because it takes 17 or 13 years for new adults to emerge en masse in spring. It takes 2-3 years for dog-day cicada nymphs to complete their development; however, some adults emerge every year due to overlapping generations. The adults appear sporadically throughout the “dog days” of summer usually beginning in July.
Like their periodical familial cousins, dog-day cicada males also "sing" to attract females. However, they do not "chorus" with large numbers synchronizing their song. An occasional dog-day cicada buzzing to entice a female doesn't compare to the cacophony created by a multitude of periodical cicadas; a barbershop quartet doesn't compare to a million man chorus!
As with periodical cicadas, dog-day cicada females use their long, spade-like ovipositors to insert eggs through the bark of twigs and into the white wood. The resulting damage splits the bark and white wood leaving deep longitudinal furrows of ruptured tissue. The injury often causes the twig to die, the leaves to turn brown ("flag"), and the twig to detach and drop. However, owing to the smaller numbers of dog-day cicadas, their egg-laying damage usually goes unnoticed.
Cicada killer wasps measure 1 1/8 to 1 5/8" in length and are one of the largest wasps found in Ohio. As with all hymenoptera (wasps, bees, etc.), only the females possess stingers (ovipositors); however, they are not aggressive. The males are aggressive, but they lack stingers.
The females spend their time digging and provisioning burrows with paralyzed cicada-prey. They prefer to dig their brood burrows in bare, well-drained soil that is exposed to full sunlight. Although the wasps are considered solitary, all of the females have the same nesting requirements. So it is not unusual for there to be numerous burrows, and wasps, in relatively small areas.
The males spend their time establishing and defending territories that encompass multiple females. They are notoriously defensive and will aggressively buzz any transgressor who dares to enter their territory including other males as well as picnickers, golfers, volleyball enthusiasts, and gardeners. Fortunately, it's all a rouse since they lack the necessary equipment to deliver a sting.
Cicada killer wasps feed exclusively on dog-day cicadas, so they are considered beneficial insects. However, their large size coupled with low-level flights over sand volleyball courts, sparse lawns, and bare areas in landscapes can be disconcerting generating demands for control options.
I have not seen a single cicada killer this season. While they may still appear on the scene, new wasps generally emerge from soil burrows slightly before or at about the same time as dog-day cicadas; a macabre welcoming committee. Areas where I've seen multiple burrows in the past are showing no activity. I did notice the soil remained wet for a number of weeks this spring. Perhaps heavy spring rains drowned the developing wasps or the high soil moisture made the immature wasps susceptible to fungal disease. Of course, this is pure unabashed speculation; the wasps may still show up … to the dismay of dog-day cicadas.