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13-year or 17-year cicadas?

13-year or 17-year cicadas?

This year, the state of New York witnessed the massive emergence of three species of periodical cicadas, which have a life cycle of 17 years. A few weeks ago, I travelled to the US east coast to observe this unique, magical phenomenon. I reported my observations in this first blog(in French only). In this one, I will give you more of an explanation of this emergence, which will not be seen again for another 17 years!

There are seven species of so-called periodical cicadas—four with a life cycle of 13 years, and three of 17 years. They are often known as “13-year cicadas” and “17-year cicadas.” In 1928, “Cicada Man” William T. Davis changed the genus name of these species from Tibiceni to Magicicada. This spring, the three “17-year cicada” species (Magicicada septendecim, Magicicada septendecula and Magicicada cassini) emerged simultaneously.

Very discreet development

Cicadas develop underground, unseen and undetected, for 17 years. So what happened this year, from North Carolina to Connecticut, is that the nymphs that had been developing since 1996 emerged from the ground. At that time, the females laid eggs on tree branches, in slits they had made themselves. After a few weeks, tiny nymphs hatched from them before dropping to the ground and burrowing down about 30 cm. They then began to grow, feeding on sap from the roots around them. 17 years later, after going through five stages of development, they were ready for the final moulting at the adult stage.

The mating chorus

When the temperature rises above 17°C, the nymphs begin to dig their way out of the soil—sometimes thousands of them at once! They then quickly climb to a suitable place (tree trunk, branch, etc.), where they can undergo their final moulting to enter the imaginal stage. The newly transformed adult remains immobile for four to six days; this is the teneral stage. Then the cacophony begins! Once the teneral stage is complete, the functional males commence their courtship. Using a pair of timbals under their abdomen, they produce a characteristic sound in the hope of attracting a female. Receptive females reply by clicking, which prompts the male to “sing” again to signal his approach. The female clicks again, and the male sings a third time to indicate he is taking action. The song of a single individual can be nearly 100 decibels in volume—imagine thousands of them singing all at once! Spectacular!

Mission accomplished

Unlike females, males can mate more than once. After fertilizing her, the male inserts a plug into the female to ensure only his genes survive before setting off in search of more females. The female, meanwhile, looks for places to lay her eggs—as many as 600 of them.

In just a few weeks, the males fertilize as many females as they can, while the females lay as many eggs as they can. Once that is done, it’s mission accomplished.

The next generation’s chorus will be heard in 2030—don’t miss it!

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