Periodical (17-year) and Common (Annual or Dog-Day)
Barbara J. Bromley, Mercer County Horticulturist
Are you planning a bridal reception or graduation picnic in your backyard for May or June? Do you attend daytime ball games for your child’s baseball league? If you live in any one of several relatively small locations in New Jersey*, perhaps you should re-think your plans. The year 2004 from May through June into July is the expected emergence of Brood X (ten) of the periodical or 17-year cicada. The last emergence of this brood was in 1987 and was memorable for those who lived in these areas. Millions of cicadas were flying into each other and people, were colliding with windows, were panicking drivers, and were generating a mind-numbing high-pitched racket. Plus, the hotter the day, the louder the noise. There were so many nymph skins on the ground under trees that it sounded like popcorn underfoot.
You might say, “But we have cicadas every summer. What is the difference?” or “I heard these are locusts. Are they the same as the Biblical plague?” The cicadas we have each year are the dog-day cicadas (Tibicen linnei) that have overlapping two- to five-year life cycles and emerge to “sing” in the trees in the “dog-days” of July and August. The dog-day cicada is about 1 5/8 inches long, has a black body with whitish bloom, green wing margins, and light markings on the thorax and abdomen. Emergence is just before that of cicada killers which are large wasps that paralyze dog-day cicadas then drag them into the ground as a food source for their young. Cicadas are related to aphids and leafhoppers and have sucking mouthparts. Locusts are closely related to grasshoppers and katydids and have chewing mouthparts. Periodical cicadas were sometimes called locusts because they emerged in such huge numbers that the colonists equated them with the plant-destroying locust.
The adult periodical cicada (Magicicada septendecim) is about an inch long. Most of the body is black, the transparent wings have orange veins, and the legs and eyes are reddish. The immature stage, or nymph, that spent seventeen years underground sucking sap from tree roots starts creating one inch tall “chimneys” or cones of soil in April and peers out of the half-inch hole to scout the surroundings, returning back underground. Finally it emerges at dusk one night in May and promptly crawls up the nearest upright structure (usually a tree), hooks its clawed “feet” into the bark, and splits its skin or exoskeleton along the back. The emerged adult cicada spends the rest of the night turning a darker color and drying its wings so it can fly. The range of flight is about a half mile. Within a week it mates.
The female then lays her eggs in slits she creates near the ends of slim branches of over 25 species of favored trees and shrubs. To do this she uses a saw-like egg-laying device called an ovipositor that is attached to the end of her abdomen. Each female lays about 500 eggs, which hatch in about seven weeks. The tiny nymphs drop to the ground, burrow in, and spend the next seventeen years sucking small amounts of sap out of tree roots and molting through several growth phases called instars. By midsummer the branch tips turn brown, die, and eventually break off at the egg-laying site, a kind of natural pruning.
The 17-year cicada is known to exist only in the central and eastern United States. (There is also a 13-year race found in the South.) Each year marks the emergence of a different brood designated by Roman numeral. Brood I was first recognized in 1893, Brood II in 1894, Brood III in 1895, and so on. Some broods are small, some large, and some now extinct or inconsequential. Brood II had its most recent sighting in parts of northern New Jersey and other states in 1996. Brood X, the largest brood, had very impressive sightings in parts of New Jersey (especially the Princeton area) and other eastern states in 1987.
So what do we do? First, don’t be alarmed or frighten your children. Periodical cicadas aren’t everywhere, they don’t bite people, and they are fascinating to watch. They either don’t feed at all as adults or simply suck small amounts of sap. Children love to collect the shed nymph skins. The tremendous noise of millions of male cicadas thrumming at the same time can be made tolerable with a very good set of earplugs. The damage done by the female egg-laying in large trees is negligible. Because young trees don’t have too many branches to start with, it is recommended that the planting of new trees and shrubs be delayed until after the cicadas have finished egg-laying. Transplants already in the ground can be protected with fine netting or cheesecloth until mid-summer. Many birds love cicadas for dinner, so providing a water source and a few birdhouses may encourage the birds to stay around. Hopefully, feeding by birds will reduce the number of dead and decaying cicadas that will litter the ground and clog gutters before summer is over.
There are a few labeled pesticides, but spraying trees is generally not recommended except in commercial apple orchards. However, leaves and twigs that turn brown can be pruned out before the nymphs drop to the ground to stave off the 2021 population. Daytime outdoor parties should be planned for unaffected communities or delayed until August. All things considered, this emergence is truly a miracle of nature. Field trip, anyone?
* The author was present for and very aware of the emergence in Princeton in 1987, but has only anecdotal evidence of populations in other parts of New Jersey. In 1974 John B. Schmitt published research on the 1970 Brood X emergence. At that time infestations in small areas of Mercer, Somerset, Hunterdon, Warren, Burlington, Salem, and Monmouth Counties were noted. Habitat influences whether those populations continue to survive. Undisturbed woodland areas and residential properties have the greatest potential for continued survival of the periodical cicada. Community development and construction in those areas since 1970 has probably eliminated populations. To find out if your neighborhood had an emergence in 1987, call your local Rutgers Cooperative Extension office, Master Gardener Helpline, or newspaper archives at the local library. In any event, you will have your answer by early June.
IPM CONTROL STRATEGIES: Periodical Cicadas
|Biological||Encourage birds that will feed on cicadas by providing water and nesting sites|
|Cultural||Do not plant/transplant trees or shrubs during the spring or summer of emergence in affected areas.|
|Mechanical/Physical||Prune out branch tips where egg laying has occurred before the tiny nymphs drop to the ground. (This will reduce the population in 2021)|
|Chemical – indoors||Not needed|
|Chemical – outdoors||Generally not recommended, but carbaryl (Sevin) can be sprayed on tree branches to reduce egg laying.|
Other cicada trivia
- As many as 20-40,000 cicada can emerge from under one large tree. Up to 104 nymphs can be found in a square foot of soil under apple trees.
- There may be as many as 1,500,000 cicadas per acre.
- Strong winds may move cicadas beyond the ½ mile flying radius.
- They are edible, especially when newly emerged from the nymph skin and before the exoskeleton hardens.
- They may burrow as deep as 1 ½ to 2 feet underground to spend the 17 years, but may be only 3-18″ deep in an orchard.
- Favored egg laying sites are oak, hickory, apple, peach, birch, hawthorn, black locust, ash, maple, pear, and grape.
- Egg laying is at its peak by June 10. Egg hatch occurs by the end of July.