Vol. 18 Issue 2, Summer 2013
By Emily Bzdyk
In 2004, when I was graduating from high school, a group of periodical cicadas, Brood X, made its appearance in Loudoun. I remember the strange-sounding chorus made by thousands of cicadas looking for a mate and it captivated me. There are few natural phenomena that equal the awesome numbers and fascinating timing of the periodical cicada’s life cycle. This year, Brood II is taking the stage. It last emerged along the East Coast just as Loudoun Wildlife Conservancy was getting its start in 1996.
Periodical cicadas are different from the green colored annual cicadas we see each summer. Our annual cicadas are bigger and come out later in the summer. The striking red-eyed periodical cicadas are slightly smaller and emerge every 17 years in early May. This year, cold spring weather gave them a bit of a late start. Unlike Brood X, Brood II does not emerge as widely in Loudoun County. Some may show up in the southern part of the county, but the largest numbers are found further to our south. I saw my first of this batch while walking in Manassas National Battlefield in mid-May. Once I saw one, I immediately noticed hundreds more! They had just emerged and were perching on blades of grass in the fields. As the air temperature warmed, they began to take flight.
These insects spent the last 17 years underground as immature nymphs, feeding on tree fluids from the roots, and slowly growing. There are about 15 broods in total, each with their own geographic range and 17-year cycle. Each brood emerges in synchrony, en masse. Why so many at once? Periodical cicadas use large numbers to overwhelm predators. The animals that eat the cicadas can feast on them and get their fill, and yet there are still plenty left to carry on the next generation.
The warmth of spring triggers the waiting nymphs to crawl out of the ground. They dig themselves out backwards, abdomen first and crawl up a tree trunk, or piece of grass or other plant material to shed their exoskeleton. The vulnerable adult expands its wings and waits for its new white exoskeleton to harden and darken. The adults then climb or fly up into the trees and begin to sing. Males and females locate each other using sound. Males create the loud whirring chorus. They use structures called tymbals that vibrate and resonate in the base of the hollow abdomen to make the sound. Females communicate using a short clicking noise. You can sometimes trick the males into singing for you by snapping your fingers near them. Once they find each other, they mate and the female uses her sword-like ovipositor to lay eggs in the twigs of trees. The eggs hatch and tiny white nymphs fall to the ground and burrow in for the long underground wait.
Adult cicadas are harmless to people and other animals. Occasionally, due to their overwhelming and concentrated numbers in some areas, the cicadas’ egg-laying and feeding can damage young or sensitive trees, but rarely is this a major problem.
As an entomologist, periodical cicadas delight me! Listening to the chorus and watching the cicadas fly among the trees can be enjoyable. However, many people do not share enthusiasm for this natural event. The large numbers of these insects can be disturbing and annoying. Those with an aversion can take comfort in the fact that the cicadas are not here for very long. In mid-June they will be finished mating and laying eggs and we will no longer hear their chorus. Cicada enthusiasts will have to wait for 2021, when the massive Brood X returns to Loudoun County.
For more information about periodical cicadas, check out these links:
This site has a great map and form to record cicada sightings: http://project.wnyc.org/cicadas/
Test your knowledge of Cicadas–try our Cicadas Crossword Puzzle.