nymph molt ovipositor

You would have to have lived underground for months not to know that 2004 is the spring of the cicada in the Chesapeake Bay watershed. In late May, a large brood of 17-year cicadas will come of age and complete their final molt, emerging from holes underground to spend their final hours singing and reproducing in the open air. Millions of the insects will fill the forests and suburbs of 12 states with the sound of their mating calls, and females of the species will insert their eggs in the twigs of trees before dying off after about two weeks of noisy activity.

Periodical cicadas are flying insects belonging to the order Hemiptera, whose closest relatives are the tree- or leafhoppers. There seven species of periodic Magicicada: four with 13-year life cycles, and three with 17-year cycles. The brood that emerges this spring, the species Magicicada septendecim, or 17-year cicada, is known for the strident, scraping ‘song’ produced by males during mating season. Unlike their close relatives the grasshopper and locust, cicadas do not strip plants of their leaves. Like the the annual cicadas that emerge in the Bay watershed toward the end of summer, they produce intense acoustic signals that can drown out other sounds, using specialized organs called tymbals on their abdomens.

There are about 13 broods of 17-year periodical cicadas and another five broods of 13-year cicadas. The “Big Brood” has an exceptionally broad range, stretching south along the East Coast to Georgia, Tennessee and Missouri, north along the Ohio Valley, into Michigan, northeast to New York and New Jersey.

In the process of laying eggs in large numbers, cicadas can cause twig breakage to shrubs and trees, known as ‘flagging’. Most mature plants survive with minimal distress, but it’s also possible to protect younger plants before the cicadas emerge, by covering them with cheesecloth. Cicadas are harmless to people; they don’t sting or bite defensively and only land out of convenience, delivering a nibble that might feel like a pinprick.

The long life cycle of the cicada begins after the eggs hatch and the juvenile cicadas, or ‘nymphs’ fall to the ground:

Photo courtesy of Gaye Williams, Maryland Department of Agriculture

• Nymphs burrow into the soil and suck fluids from the roots of trees and shrubs for nourishment.
  
  
• They require 13 to 17 years to complete development. At the beginning of this period, each nymph crawls to nearest upright support, sheds its skin, and begins its slow transformation to an adult.
  
  
• Magicicada species undergo five juvenile stages during their 17-year life cycle underground.
  
  
• During those years they grow from the size of a small ant to nearly their adult length of about 1 1/8 inches long, with wingspans of up to 3 inches.

• In the spring of their 17th year, nymphs build exit tunnels to the surface. These holes in the ground and are about ½ inch in diameter; sometimes they resemble small mud chimneys or turrets.
  
  
• The night they emerge, nymphs leave the burrows around sunset and settle on nearby vegetation to complete their final molt.
  
  
• When this molt is complete, the new exoskeleton of the adults may appear white, but will darken as it hardens.
  
  
• A large segment of the population may emerge in a single night.
  
  
• Newly molted adult cicadas climb the bark of trees and may spend several days as ‘teneral’ adults until their exoskeletons harden completely.
  

Photo courtesy of The University of Maryland

• Soil temperature appears to influence the timing of the cicadas’ emergence; nymphs tend to emerge when soil temperature outside the tunnel exceeds about 64 degrees F.
  
  
• Cicadas in warmer regions will thus tend to emerge sooner than in the north; for example, in South Carolina they may begin to emerge in late April, while in southern Michigan not until June. Nymphs in the mid-Atlantic region tend to appear in mid- to late May.
  
  
• The simultaneous emergence of tens of thousands of cicadas during a few weeks overwhelms predators, permitting most of them to mate undisturbed.
  
  
• When the teneral phase is complete, males begin to produce their intense, whining songs and choruses to attract females. During this time all cicadas will continue to feed, usually on plant juices.
  
  
• Mated females use their ovipositor to slit y-shaped egg nests into the bark of living twigs and lay as many as 20 eggs in each nest. A single female may lay up to 600 eggs.
  
  
• After 6 to 10 weeks, the eggs hatch and the nymphs drop to the ground, beginning their long cycle underground.

Magicicada adults do not resemble those late-summer annual cicadas, which appear iridescent or green; the 17-year brood that emerges in May will have black bodies and striking red eyes and orange-veined membranous wings, with a black ‘W’ near the tips of the forewings. Their legs are also reddish, and the under surface of the abdomens are reddish brown to yellow.

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Last modified: 06/01/2004