Animals have developed a wide variety of defensive strategies to avoid being eaten by predators. Some of these techniques, such as camouflage, decrease the organism’s chance of being spotted by a predator. Others, such as aggregation, deter predators from attacking. The most dramatic of defenses is predator satiation, in which members of a species emerge in such high densities that predators simply cannot consume them all (1).
One species that uses this defense is the periodical cicada, an inch and a half long winged insect with a black body and bright crimson eyes (3). There are several species of periodical cicada that live throughout the eastern United States, with life cycles of either 13 or 17 years.
The cicadas that inhabit the northeast spend their first 17 years underground as juveniles, or nymphs. They feed on fluid from plant vascular tissue and dig to the surface once they mature. Aboveground, they molt and develop a hard adult exoskeleton.
The emergence of periodical cicadas is so well coordinated that as many as 1.5 million per acre can appear practically overnight. To achieve such synchronized movement, the juvenile cicadas wait until the soil reaches a certain temperature before emerging (2). Once they have become adults, males fly to treetops and sound their mating calls, using the ribbed vibrating membranes on their abdomen (3).
After mating, females lay up to 600 eggs in nests that they dig out in tree branches. The adults die shortly after, and the young fall to the ground when they hatch, burrowing underground to start their long development process (2).
During these mass emergences, cicadas swarm in such high densities that predators can eat their fill without making a dent in the cicada population. The predator populations cannot grow in response to the increase in prey supply, because the cicadas are only available as a food source once every seventeen years (2). Thus, population dynamics of other species are not greatly affected by the cicadas.
This summer, juveniles that have been developing since 1996 are scheduled to swarm in the northeast, from Georgia to New York. Dense concentrations of cicadas should reach central Connecticut by late May or early June. Although these insects may appear alarming, they do not sting or bite, are not toxic, and do not transmit disease (2).
1. M. C. Molles, Ecology: Concepts and Applications (6th ed. New York: WCB/McGraw-Hill, 2013). [sixth edition]
2. “General Periodical Cicada Information.” Magicicada.org. N.p., 18 May 2013. Available at http://magicicada.org/magicicada_ii.php (18 May 2013).
3. Z. Howard, They’re Back: 17-year Cicadas to Swarm from Georgia to New York (5 May 2013). Available at http://www.reuters.com/article/2013/05/05/us-usa-cicadas-idUSBRE94407020130505 (18 May 2013).