And its back to the busy survey season with the first newt survey of the year completed. Last week we said hello to the slow paced Triton’s Trumpet and its deadly prey the Crown of Thorns Starfish. This week we have an ear-splitting request from @bella_blackstar, hope you guys enjoy.
Issue #166 – Pharaoh Cicada
Kingdom – Animalia
Phylum – Arthropoda
Class – Insecta
Order – Hemiptera
Family – Cicadidae
Genus – Magicada
Species – septendecim
Related Species - The Pharaoh Cicada is one of seven species known collectively as the Periodical Cicadas.
Range - Pharaoh Cicada can be found in parkland and treelines throughout the Eastern Seaboard of the United States and Canada
Seventeen Year Locust?
Pharaoh Cicadas are the largest members of the genus Magicada with the adults reaching a body length of almost 4cm. The adult cicadas have black bodies with large red eyes and orange wings, while the nymphs are pale wingless versions of the eventual imago. The nymphs are largely subterranean, feeding on the roots of the trees that their eggs were laid on, and moult at least five times over the course of seventeen years (2). During the seventeenth year in late April the nymph will tunnel up to the surface at night and complete one final moult where it becomes a winged sexually mature adult.
The nymphs of all seven species of the Periodic Cicadas emerge in large ‘broods; over the course of a week, and while initially vulnerable to predation the sheer number of insects mean any losses prior to breeding are inconsequential. While largely defenceless, the Pharaoh Cicada can release a warning call that alerts nearby insects to the presence of potential danger, and when pressed cicadas can deliver a painful bite. The calls the insects are most known for however, are their nuptial call which can reach over 100dB in volume and sounds like the word ‘Pharaoh’ and is likely the reason for their colloquial name. The species is also known as the Seventeen-Year Locust but it should be noted that locusts and cicadas are from completely different orders, and produce their calls in completely different ways.
All cicada calls are generated by the insect vibrating a membrane known as a ‘tymbal’ located on the top of the abdomen to make a clicking sound. Combining the movements of the tymbal with the (largely) hollow abdomen and the resonating chambers in the trachea, the cicada can make an almost continuous song. Different species of cicada call at different times of the day, with the Pharaoh Cicada calling during the hottest part of the day (3). Once a males crescendo attracts a female they quickly mate, and the female finds a twig and chews a hollow in the bark, in which she lays her eggs. Adult Pharaoh Cicadas have relatively short lifespans, with most of the insects dead by the time the eggs hatch, and the nymphs drop off their nursery trees between late June and mid-July.
Ecology 101: A Guide to Environmental Mechanics #17 - Cicadas and Prime Numbers
In 1749 Pehr Kalm, a Swedish entomologist visiting the United States observed a massive emergence of cicadas in both New Jersey and Pennsylvania, but on returning to the same area a year later in 1750, he found that the insects were nowhere to be seen. In an attempt to investigate why the cicadas were not active in 1750, Kalm scoured the archives and cited sources, including Benjamin Franklin, about the periodic nature of cicadas about the appearance of the insects in 1715 and 1732, eventually coming to the conclusion that the cicadas or ‘locusts’ as he called them only appeared every seventeen years (4).
Further observations would later confirm that the species Kalm had witnessed were indeed tied to a seventeen year cycle. However, such a cycle is not found in all cicadas, with the vast majority of species classed as annual cicadas with much shorter lifespans of between two to ten years, and who appear every summer. Only the cicadas from the genus Magicada have fixed synchronised lifecycle tied to either thirteen or seventeen years, both of which are prime numbers. Of the seven species three take seventeen years to mature, and the remaining four take thirteen years to reach adulthood.
The reason for such a long lifespan, at least in the modern day, comes down to a response for predation. While cicadas face a lot of predation when they emerge from underground, not just from specialised cicada predators such as the Eastern Cicada Killer (Sphecius specosis), but also from generalist feeders such as songbirds, lizards and foxes to name but a few. Because the aforementioned predators have relatively short lifespans however, they are unable to synchronise their own breeding seasons with that of the cicadas, thus ensuring that the cicadas will always outnumber any potential hunters by such a large margin that a single brood can lose thousands of individuals and yet still remain healthy.
Outlasting their predators is however, not the reason such long periods between cicada nymphs hatching and then maturing into adults exists. Instead, such long developmental periods probably come down to a survival response relating to an increase in glacial action in the last four million years when these insects evolved (5). Current distributions show that the three most northerly species of periodic cicada mature on a seventeen year cycle, while more southerly species mature on the thirteen year cycle. Both groups can probably owe their slow maturation periods to cold soil temperatures slowing their development into adults, as evidence on how changes in local temperature can slow or speed up the development of other species of insect.
This year only a single cicada brood, Brood VI, is scheduled to emerge this year, and is set to emerge in Northern Georgia and Carolinas sometime in late April or early May. Because of their fixed terms, cicada emergence's can be accurately mapped for decades, even centuries into the future.
2 - Marlatt, C. L. (1907). The Periodical Cicada (Bulletin No. 71 - U.S. Department of Agriculture, Bureau of Entomology). Washington, D.C.: United States Government Printing Office. pp. 123–12
3 - Turpin, Tom (11 September 2008). "Sound of Insect Music Ushers in Fall Season". Purdue University
4 - Davis, J.J. (May 1953). "Pehr Kalm's Description of the Periodical Cicada, Magicicada septendecim L., from Kongl. Svenska Vetenskap Academiens Handlinger, 17:101-116, 1756, translated by Larson, Esther Louise (Mrs. K.E. Doak)". The Ohio Journal of Science. 53: 139–140
5 - Teiji Sota; Satoshi Yamamoto; John R. Cooley; Kathy B. R. Hill; Chris Simon; Jin Yoshimura (2013). "Independent divergence of 13- and 17-y life cycles among three periodical cicada lineages". Proceedings of the National Academy of Sciences of the United States of America. 110 (2): 6919–6924
1 - https://c1.staticflickr.com/4/3782/8931258551_16d7fd65bc_b.jpg
2 - http://www.cuyahogaswcd.org/files/blog/slideshow/where-nymph.jpg
3 - http://bugguide.net/images/cache/5LV/ZXL/5LVZXLBZHLHRMH1HPHLRPH1HIHTHQL6Z0L8ZLLNZ2HZRWHFHEHLRMLAZ5L3H7LAZ4L9ZNHAZ5LEZRL8ZQL1ZPHYHML.jpg
4 - http://news.nationalgeographic.com/content/dam/news/photos/000/657/65791.jpg
Talk about a mysterious emergence indeed, if the screaming of the cicadas doesn’t do your head in, trying to figure out the reason for the maths behind it will. Next week grab your time machines and mosquitos entombed in amber because we have a tyrannical issue of IGTA, but until then make sure to critic, comment and suggest future issues as well as making sure you check past issues in Impurest’s Bestiary