The last time trillions of cicadas plagued the United States, Napoleon was planning to invade Britain and in Germany, the infamous robber captain “Schinderhannes” was sentenced to death and beheaded.
That was in 1803. In 2024, Napoleon and Schinderhannes will long be history, but people in the USA will once again have to contend with a huge plague of cicadas. As was the case back then, song cicadas from “Brood XIII” and “Brood XIX” have already dug upwards in masses from deeper layers of soil. The animals of the genus Magicicada are just waiting to emerge together. This will probably happen at the end of April.
We know all this so precisely because the two to three centimeter long, red-eyed insects stick to a precise schedule. Cicadas from brood XIII come to the surface every 17 years, the animals from brood XIX every 13 years. What’s special this year: The release dates of the two broods overlap, and that only happens every 221 years. “It will be interesting,” says Swiss singing cicada expert Thomas Hertach.
An exciting question, for example, is whether the animals from different broods mate with each other. And whether new species or even new broods might emerge. This year, scientists may also come closer to solving the mystery of why these periodic cicadas, found only in the United States, live underground for so many years before venturing out into the light of day.
“One theory is that this is a strategy to avoid predators,” says Hertach. “No bird or mammal is able to adapt to such a long cycle.” If the cicadas appeared at shorter intervals, for example every two years, there would soon be animals that produce a particularly large number of offspring in these years, which could then easily be fed with huge amounts of cicadas.
The good news for people in the affected regions is: the cicadas are not dangerous. They don’t bite, they don’t sting and they don’t transmit diseases. However, they are loud: in order to attract females, the male cicadas make a deafening noise. “It can be as loud as a moving truck,” says Göttingen entomologist Herbert Nickel. “To amplify the sound produced by a special drum organ in the abdomen, song cicadas have special air sacs. Each male wants to be louder than the others.” For the insects, the whole spectacle has only one purpose: to mate. And whoever chirps the loudest gets the most females.
The insect invasion has an extremely positive effect on nature
The so-called cicada rain that drips from the trees on which the animals sit en masse and sip plant sap can also be unpleasant for people. What they can’t use, they simply drop.
For birds, squirrels and some other animals, however, the masses of cicadas are a feast. In general, the insect invasion has a rather positive effect on nature: the tunnels that the animals dig when they burrow out into the open ventilate the ground. And when the singing cicadas die after a few weeks – “locally there are almost mass graves,” says Hertach – their carcasses act as fertilizer, boosting the growth of many plants.
Before the insects die, each female lays hundreds of eggs in small slits that she carves into the bark of branches. After a few weeks, larvae hatch. They drop to the ground and disappear into the earth. As if nothing had happened.