“Lou Soleu me f’E f’E fê Canta” (“The Sun makes me sing”), wrote Frédéric Mistral, a great figure in Provencal literature, to celebrate the attachment of the cicada to the culture of the Midi and highlight its essential place in the sound universe of the region. However, although part of our imagination in the summer of the south of France, the Cigale is an insect present in many regions of the world, especially in the United States, where certain species have a remarkable life cycle, both long and perfectly synchronized.
Recognizable in their bright red eyes and their orange wings, the periodic east cicadas of the American, of the Magicicada genre (family of the cicadidae), emerge from the soil by millions after having passed thirteen or seventeen years underground in the larval state. Among the fifteen cohorts of periodic cicadas identified through the United States, only one emerged each year in the spring.
Stéphane Puissant, main conservation attaché at the Dijon Natural History Museum, explains that there are “two groups of species: a group that emerges every thirteen years”, composed of three species, “and another which emerges every seventeen”, which has twelve. The simultaneous earth exit of two cohorts from these different groups constitutes, according to him, “one of the most impressive phenomena in terms of density, quantity of individuals”, even if it specifies that “what we see represents only a tiny part of what is in the soil”.
This massive population movement, comparable to the vertical migrations of zooplankton in the oceans, is one of the biggest events [naturels] of the planet, to see once in his life ”. The appearance of this phenomenon obeys a precise mathematical logic and only occurs the two hundred and twenty -one years. The specialist recalls, however, that each year, a single cohort of cicadas comes out of the ground: a less impressive event, but which still concerns millions of individuals.
“The species that appear every seventeen years are distributed in the north of the United States and to Canada, [tandis que] those that emerge every thirteen years [se trouvent] Rather in the southern half of the United States, ”says Stéphane Powerful. “One of the main theories that explain this periodicity of appearance of species is the presence [passée] glaciers. […] Another theory [évoque le rôle de certains] parasites, which would have selected the period of appearance of adult cicadas, ”continues the researcher.
“The cicadas [périodiques] spend most of their lives in the ground. They are therefore endowed, ”explains the scientist. It is there, in the darkness of the basement, “that they will grow, before transforming to arrive at the stadium of young nymphoids”. This step precedes their emergence: young cicadas “come out of the ground, cling to a support, to transform and give the imago”, that is to say “the adult sexually ripe, capable of reproducing”.
During their life cycle, “we have a [première] Phase, aerial, that of adults, which is very short in time, one to two weeks maximum “, during which the risk of predation is particularly high. “The longer the life cycle of cicadas, the more likely they are to escape predators. […] Because when a life cycle underground is long, counts in number of years, obviously, predators will not only have time to die, and above all, to forget the presence of cicadas. This does not mean that they will not adapt later, “said Stéphane Powerful.
