They’re Back!!!! Periodical Cicadas

Periodical cicada is set to emerge in the Chicago area and should do so by early June. Periodical cicadas feed for years as nymphs on the sap of roots of trees and shrubs. From central Illinois south they emerge above ground on the thirteenth year, molt into adults and reproduce. From central Illinois north, they emerge on the seventeenth year. This year’s is an unusual emergence that started in 1969 when part of the northern Illinois brood emerged after thirteen years in northeastern Illinois instead of seventeen years. Since then, this group of cicadas has emerged every seventeen years so there was an emergence in 1986 and will be again this year. In 2007, northeastern Illinois will experience the rest of the emergence of this brood along with most of the rest of the northern third of Illinois.

We expect the periodical cicadas to emerge through much of the Cook County suburbs, the eastern half of DuPage county, southeastern Lake county and northeaster Will county. The expected emergence is a curved band running from Deerfield on the northeast, arcing to Addison and Lisle on the west and arcing to Crete on the southeast. The inside of the band arcs across northwestern, western and southwestern Chicago.

Full-grown nymphs are brown, humpbacked and about three-quarters inch long. They commonly construct soil chimneys that extend from the ground up to three inches high and are about one-half inch in diameter. These chimneys have been reported in the last part of May this year in the expected emergence area. Chimneys are not always constructed. Within a few days, the nymphs break through the top of the chimneys or soil surface to crawl up trees, shrubs and other upright objects where they molt into adults. Adult periodical cicadas are about one and one-quarter inch long black insects with red eyes and orange-veined, clear wings.

Males produce a high-pitched wavering song that sounds like a trill when many are singing together. They sing primarily during the sunny part of the day to attract females to them for mating. The males and the singing die after a couple of weeks, while females remain alive for two to four weeks longer to lay eggs. Eggs are inserted into tree and shrub stems that are up to two inches in diameter. Heavy egg laying will cause twigs to break, resulting in dead leaves at the end of branches. Small trees may have enough eggs laid into the trunk that it breaks off.

Control is directed at preventing egg-laying damage, as adult feeding is insignificant. Although pyrethroids and carbaryl (Sevin) will kill large numbers of adults, treated plants commonly experience about as much injury as untreated plants in landscapes and small planting areas. In nurseries and other large planting areas, repeated applications could reduce the damage significantly. Individual trees can be protected with nylon netting or wire screening tied around the trunk and larger branches. Make sure that the netting or screening stands out from the trunk so that the cicadas cannot reach the stem with their ovipositors. Although damage to small branches is obvious, its long-term effect will be to make the plant bushier and is not usually worth control efforts.

Eggs hatch within a few weeks into small nymphs that drop to the ground and tunnel down to find a root to feed on. Over the years, nymphs will commonly move to different roots, but do not migrate very far. The nymphs have little effect on tree health, although studies have shown reduced diameter growth in trees during the last two to three years before adult emergence. Because larger insects eat more than smaller ones, older, larger nymphs apparently eat enough sap to reduce growth.

I would like to know where these cicadas are found. Call 773-233-0476 or e-mail me at rwolford@uiuc.edu

Source: Philip Nixon, Entomology, University of Illinois

June 2003
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