There was lots of press coverage recently about Brood X, the 17-year periodical cicada emerging by the millions from the ground in 15 states, including Maryland, Ohio, Indiana, Pennsylvania, Virginia, West Virginia, Kentucky, Georgia, and elsewhere. The males of these harmless insects can make a whole lot of noise when they call together to attract females. Their “wee-oh” calls remind me of a sci-fi movie scene when aliens are attacking!
There are three species of periodical cicadas. In Connecticut we have the largest, which is the Decim Periodical Cicada or Linnaeus’s 17-Year Cicada (Magicicada septendecim). This brood, Brood II, last hatched in 2013 and won’t be hatching here again until 2030.
A periodical cicada spends either 13 or 17 years below the ground as a nymph sucking on juices from the roots of trees. Trees usually are not harmed by this feeding. When it is their time, the insects emerge en masse. Some scientists theorize that they do this to overwhelm predators such as amphibians, birds, and raccoons. Cicadas provide a good amount of high protein food, but with so many emerging at once many escape being eaten to carry on the species.
Cicadas emerge when the ground temperature reaches 64 °F (18 °C) at a depth of 8 inches (20 centimeters). The nymphs emerge from the soil and crawl up a tree or shrub. Then their nymphal “skin” cracks down the middle and the adult emerges.
Some call these insects 17-year locusts, which is a misnomer. Locusts are a type of short-horned grasshopper from the order Orthoptera. Cicadas are members of the order Hemiptera, the true bugs. They are closely related to leaf hoppers and plant hoppers.
Males attract females with their calls, which they make by contracting muscles in their abdomens. These muscles cause a tymbal membrane to buckle and make a clicking sound 300 to 400 times a second and as loud as up to 100 decibels!
After the winged adults mate, the female deposits 300 to 400 eggs in a slit she cuts in the bark of a twig or branch. A large swarm can damage a small tree by this egg laying and by the adults feeding on sap, but larger trees are not harmed. After the eggs hatch, the larvae drop from the tree and burrow into the ground. The adults die four to six weeks after mating.
A periodical cicada brood’s simultaneous hatches, with the males’ loud calls, are an amazing event in nature. But what most of us hear every summer are the annual cicadas. Like the periodical cicadas, the annual cicadas have nymphal stages that spend multiple years underground, although some species hatch every year.
There are about seven common species of annual cicadas in Connecticut. Last week I heard the Dog-day Cicada (Neotibicen canicularis). I’ve often heard this species in pine and mixed conifer woods. It sounds like someone sharpening a tool on a grinding wheel. The most common species found in the eastern United States, and the one most of us hear, is the Morning or Swamp Cicada (Neotibicen tibecen). It’s hissing “shish” call rises and falls in intensity.
Any species that spends multiple years underground and out of sight can, through time, be threatened by development. Many local broods have become extinct, such as some of Brood X on Long Island, when their resting places are paved over and built on. Thanks to the foresight of the late Yale entomologist Charles Remington, a section of land near Sleeping Giant State Park in Hamden, Connecticut, has been preserved as a cicada sanctuary. I look forward to 2030 when this amazing natural event returns to our area.