Billions of “periodic” cicadas will soon invade the East Coast of the United States to breed. The last time they came forward was 17 years ago.
Some residents of the American East Coast will soon (in April or May, depending on the latitude) witness a rare event: the emergence of billions of cicadas. These insects will emerge from the basement in a dozen states, from New York to Illinois to northern Georgia.
“As soon as the soil reaches a certain temperature, around 62 degrees Fahrenheit (almost 17 degrees Celsius, editor’s note) on an evening that could be a little humid, but not too rainy, the nymphs will start to come out of the ground and then molt”says John Cooley of the University of Connecticut at Hartford. Then, “They will hang out in the vegetation without doing much for a week. And then they will adopt adult behavior ”.
That is, for about a month, cicadas will play cymbals in wooded and suburban areas. in order to mate.
Each female will then lay hundreds of eggs in tree branches, and then all of the adults will die. Once these eggs hatch, new nymphs will fall from the trees to burrow underground … for 17 years.
We are used, especially in the south of France, to enjoy the cicadas every summer. The eggs laid during the summer season then transform into larvae which, in the fall, burrow into the ground, before emerging the following summer.
But you should also know that some cicadas have evolved to take more of their time. In the United States, there is a dozen periodic broods of 17 years in the deciduous forests of the northeast, and three 13-year periodic broods in the Southeast and the Mississippi Valley. Underground, they then feed on roots and go through the five juvenile stages of their growth at their own pace.
In The conversationJohn Cooley says that the sudden appearance of so many insects before the first American settlers in Massachusetts reminded them of the plagues of the Bible. It was only later, in the 19th century, that entomologists established that these insects, unlike locusts or other grasshoppers, did not decimate crops.
Scientists do not yet know why these “periodic” insects have adopted such behaviors. However, emerging in large numbers could increase their chances of accomplishing their main mission: finding a partner. It could also be a developed defense against predators.