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One warm summer day in 1988 Chuck Holliday, professor of biology, was walking past Pardee Hall and noticed a colony of wasps. Not just any wasps, but Sphecius speciosus, also known as “cicada killer.” The females can be up to two inches long and prey on cicadas, a familiar summertime insect. The wasps have a short life, emerging from the ground every July shortly after the cicadas; males live about two weeks and females about a month.
Remembering similar wasps from his childhood in Virginia, Holliday’s interest was piqued. He began researching the insects and found many gaps in what little was known about them. Almost every summer since, Holliday has made time to study these wasps, adding to the knowledge about the five New World species of Sphecius, culminating in a new guide to identifying the different species that was published in the September issue of Annals of the Entomological Society of America.
“These wasps build their nests underground. The females can dig a hole two feet deep,” says Holliday. “The males emerge first and wait for the females to emerge and mate with them. After mating, the females fly to a different area. There they dig a burrow, fly off to catch a cicada by stinging and paralyzing it, and bring the cicada back to the burrow. They lay an egg on top of the paralyzed cicada, and bury it alive. When the egg hatches, it eats the cicada that is still alive. It’s like Alien.”
Holliday says not to worry about these wasps if they burrow in your yard. “They won’t sting you unless you kneel right on them or step on them with bare feet.” Holliday and his cicada-killing wasps were featured Aug. 29 in The Philadelphia Inquirer and on Philadelphia’s KYW-AM news radio, and Sept. 2 in an interview with Scott Simon, host of National Public Radio’s “Weekend Edition.”
Holliday adds that the female wasp somehow knows what sex each of its offspring will be; the wasp puts one cicada with an egg that will become a male wasp, and two cicadas with an egg that will become a female wasp.
For his cicada killer publication, Holliday studied about 4,500 wasps, including 1,000 that were sent to him by people around the country in response to solicitations on his web page and an additional 3,500 loaned by museums around the world.
He has worked with four students on his summer wasp research: Gemma L. Salt ’92, Kareema J. Levetter ’94, Amith K. Majumdar ’95, and Amanda T. Parton ’98. Holliday is interested in the distribution and range of the five species of Sphecius across the country, taxonomy and DNA of the five wasp species, and the species of cicadas that appeal most to the wasps. This past summer he studied the function of large spines on the female wasp’s back legs that are used to dig burrows. He was able to prove that without the spurs, it takes the wasps longer to dig burrows and they lay fewer eggs, thus reducing fertility.
Volunteers who would like to contribute wasps and/or cicadas to his study next summer or learn more about cicada-killer wasps should visit Holliday’s web page.