On hot summer days, the pulsing drone of dog day cicadas reminds us that outside temperatures flirt with 90 degrees. It’s also fair warning to be on the lookout for a monstrous insect, the cicada killer.
By insect standards, the cicada killer is huge. Females can grow to a length of two inches and the bright yellow bands on the dark abdomen identify it immediately as a wasp. Because they are so big, cicada killers strike fear into the hearts of people who see them. But males lack stingers, and females are quite docile towards people.
Cicada killers emerge in July from their subterranean birth chambers shortly after dog day cicadas make their first appearance. Unlike yellow jackets and hornets, cicada killers are solitary. Adults live up to 75 days and subsist on nectar.
The natural history of cicada killers justifies their common name. In late July and August, females search for well drained sandy soils in which to excavate nesting tunnels. Watch for half-inch holes along sandy beaches by rivers and at ball fields, sand volleyball courts and sand traps on gold course.
After mating, females dig a tunnel 10 to 12 inches deep. At the end of the tunnel, females create a larger nesting chamber. Now the female cicada killer turns hunter. And cicadas are the prey.
The killers search trees for cicadas and probably locate them by sight rather than sound. Female cicadas are taken as often as males, and since female cicadas don’t sing, they are probably located by sight.
When a cicada is found, the female stings it and injects its paralyzing venom. After the cicada is incapacitated, the killer grabs its large victim lengthwise and glides down to its burrow. If the kill comes on the ground, the killer drags the cicada to its burrow.
An interesting question is how females find their way back to the burrow, especially when they find prey up to 100 yards from the burrow.
When females leave the nest to hunt for cicadas, they typically circle above several times. That they memorize landmarks near the nest seems a reasonable explanation.
Animal behaviorist Niko Tinbergen demonstrated the use of landmarks experimentally in a species of European solitary wasp. While the female excavated her burrow, he placed a circle of pine cones around the entrance to the burrow. When the female emerged, she made several orientation flights above the hole.
Tinbergen allowed the female to make several return trips to the burrow with small bees (this particular wasp supplies the nest with many small prey items), until he was satisfied that the wasp was visually acquainted with the ring of pine cones.
Then, after the wasp departed on another hunting trip, he moved the ring of pine cones several feet away. When the female returned, she flew to the center of the ring of pine cones and searched unsuccessfully for her burrow.
After repeating the experiment many times, Tinbergen concluded that the wasp used landmarks to visually relocate her nest. It seems reasonable that cicada killers behave similarly.
After the killer drags a cicada to the nest chamber at the end of the tunnel, she lays an egg on the still living, but paralyzed cicada. She then seals the tunnel and repeats the process many times until she dies.
After just a few days the egg hatches, and the larval killer begins eating the paralyzed cicada. By the end of summer, the cicada is consumed and the larval killer pupates and spends the winter underground. The following July adult cicada killers emerge from their cocoons, dig their way to freedom, and the reproductive cycle begins again.
Timing is critical because dog day cicadas do not emerge until July. So when the cicadas drone, cicada killers are sure to follow. And because periodical cicadas emerge and disappear by the end of June, cicada killers never encounter the periodical species.
And that’s a good thing because periodical species only emerge every 13 or 17 years. If cicada killers relied on periodical cicadas, they would starve.