Periodic cicadas

Magicicada

Magicicada is the genus of the 13- and 17- year periodical cicadas of eastern North America. These insects display a unique combination of long life cycles, periodicity, and mass emergences. They are sometimes called "seventeen-year locust"s, but they are not locusts; locusts belong to the order Orthoptera.

Taxonomy

There are seven recognized species. Three species have a 17-year cycle:

Magicicada cassini (Linnaeus, 1758)
Magicicada septendecim (Fisher)
Magicicada septendecula (Alexander and Moore, 1962)

Four more species follow a 13-year cycle:

Magicicada neotredecim (Marshall and Cooley, 2000)
Magicicada tredecim (Walsh and Riley, 1868)
Magicicada tredecassini (Alexander and Moore, 1962)
Magicicada tredecula (Alexander and Moore, 1962)

Generally, the 17-year cicadas are distributed more in the northern states of the eastern United States, while the 13-year cicadas occur in the southern states.

Description

Nearly all cicadas spend multiple years growing underground as juveniles, before emerging aboveground for a short adult stage of several weeks to a few months. The seven periodical cicada species are so-named because, in any one location, all of the members of the population are developmentally synchronized – they emerge as adults all at once in the same year. This periodicity is especially amazing because their life cycles are so extremely long – 13 or 17 years. Cicadas of all other species (perhaps 3000 worldwide) are not synchronized, so some adults mature each summer and emerge while the rest of the population continues to develop underground. Many people refer to these non-periodical species as annual cicadas since some are seen in every summer. The life cycles of most annual species range from two to ten years, although some could be longer.

Periodical cicadas are average-sized for cicadas, but they are slightly smaller than the annual cicada species found in the same regions of the United States. Imagines (or adults) have a size of 2.5 to 3 cm (1 to 1.2 inches). They are black, with red eyes and yellow or orange stripes on the underside. The wings are translucent and have orange veins.

They are harmless insects; they neither bite nor sting. They are not venomous, and there is no evidence that they transmit diseases. They generally do not pose a threat to vegetation, but young plants may be damaged by excessive feeding or egg laying. It is thus advised not to plant new trees or shrubs just before an emergence of the periodical cicadas. Mature plants usually do not suffer lasting damage even by a mass-emergence.

Broods

Periodical cicadas are grouped into 30 broods, based on the year they emerge. Broods are numbered using Roman numerals; broods I–XVII are the seventeen-year cicadas, while Broods XVIII–XXX are the thirteen-year cicadas. Some broods are known not to exist, but they are retained in the numbering scheme for convenience. This scheme was put forth by C.L. Marlatt in his classic study of 1907. Since then the actual number of broods has been recognized as 15 rather than 30.

Name	Nickname	Cycle (yrs)	Last Emergence	Next Emergence	Extent
Brood I	The Blue Ridge Brood	17	1995	2012	--
Brood II	none	17	1996	2013	--
Brood III	The Iowan Brood	17	1997	2014	Iowa
Brood IV	The Kansan Brood	17	1998	2015	Kansas, Missouri, Oklahoma
Brood V	none	17	1999	2016	--
Brood VI	none	17	2000	2017	--
Brood VII	The Onondaga Brood	17	2001	2018	Upstate New York.¹
Brood VIII	none	17	2002	2019	--
Brood IX	none	13	2003	2016	--
Brood X	The Great Eastern Brood	17	2004	2021	From New York to North Carolina along the East Coast, inland to Illinois and Michigan.²
Brood XI	none	17	(2005)	Extinct	Last seen in 1954 in Ashford, CT along Fenton River.
Brood XIII	The Northern Illinois Brood	17	2007	2024	Northern Illinois and in parts of Iowa, Wisconsin, and Indiana.³
Brood XIV	none	17	2008	2025	Southern Ohio, Kentucky, Tennessee, Massachusetts, Maryland, North Carolina, Pennsylvania, northern Georgia, Western parts of Virginia & W. Virginia, and parts of New York & New Jersey .³
Brood XIX	The Great Southern Brood	13	1998	2011	The Midwest to Maryland and Virginia.⁴
Brood XXII	none	13	2001	2014	Louisiana and Mississippi.⁵
Brood XXIII	The Lower Mississippi River Valley Brood	13	2002	2015	--
1. Consists only of M. septendecim. 2. Largest of all 17-year periodical broods. 3. Premature emergences, or "straggling" occurred in 2003 and 2006. 4. Largest of all 13-year periodical cicada broods. 5. This 13-year brood does not include M. neotredecim.

Life cycle

The nymphs of the periodic cicadas live underground, often at depths of 30 cm (one ft) or more, feeding on the juices of plant roots. They stay immobile and go through five development stages before constructing an exit tunnel in the spring of their 13th or 17th year. These exit tunnels have a diameter of about 1–1.5 cm (½ in.)

The nymphs emerge on a Spring evening when the soil temperature at about 20 cm depth is above 17 °C (63 F). In most years, this works out to late April or early May in far southern states, and late May to early June in the far northern states. Emerging nymphs climb to a suitable place on the nearby vegetation to complete their transformation into an adult cicada. They molt one last time and then spend about six days in the leaves waiting for their exoskeleton to harden completely. Just after this final molt, the teneral adults are white, but darken within an hour.

The nymphs emerge in large numbers at about the same time, sometimes more than 1.5 million individuals per acre (>370/m²). Their mass-emergence is a survival trait called "predator satiation": for the first week after emergence, the periodic cicadas are an easy prey for reptiles, birds, squirrels, cats, and other small and large mammals. The cicadas' survival mechanism is simply to overwhelm predators by their sheer numbers, ensuring the survival of most of the individuals. It has been hypothesized that the emergence period of large prime numbers (13 and 17 years) is also a predatory avoidance strategy adopted to eliminate the possibility of potential predators receiving periodic population boosts by synchronizing their own generations to divisors of the cicada emergence period.

Adult periodical cicadas live only for a few weeks—by mid-July, all have disappeared. Their short adult life has one sole purpose: reproduction. The males "sing" a mating song; like other cicadas, they produce loud sounds using their tymbals. Receptive females respond to the calls of conspecific males with timed wing-flicks, which attract the males for mating. The sounds of a "chorus"—a group of males—can be deafening and reach 100 dB.

Both males and females can mate multiple times, although most females seem to mate just once. After mating, the female cuts V-shaped slits in the bark of young twigs and lays approximately 20 eggs in each, for a total of 600 or more eggs. After about six to ten weeks, the eggs hatch and the newborn nymphs drop to the ground, where they burrow and begin another 13 or 17-year cycle. The carcasses of periodic cicadas decompose on the ground, providing a resource pulse of nutrients to the forest community.