THE BROOD X FILES
Clouds of cicadas louder than jet aircraft mass on America's east coast
May 2021 saw the latest appearance of Brood X (ten) cicadas, the biggest brood of periodic cicadas, along the east coast of America. The insects, which are up to two inches (5cm) long, appear in huge numbers every 17 years when temperatures reach 18C (65F) reaching densities of up to 1.3 million per acre as billions and possibly trillions emerge at once. Once they emerge, they shed the protective shell in which they have hibernated and set out to attract a mate, with the males making a strident buzzing sound to attract the females. At such high densities, this can be deafening; at its peak, the sound of massed Brood X cicada males calling tops 96 decibels, making them louder than a jet landing at Heathrow. Females do not sing but make a clicking noise. Cicadas seeking mates have been known to be attracted to power tools and lawnmowers. The adult cicadas do not eat, having spent their 17 years underground nourishing themselves on plant sap sucked from roots. They do, however, release excess fluid, producing what is known as “cicada rain”, prompting some people to wear wide-brimmed hats in peak years. As adults, they live for no more than four weeks, with the males dying as soon as they have mated and the females once they have laid eggs. On hatching, the cicada larvæ burrow into the ground as quickly as possible and attach themselves to plant roots, where they will stay nourishing themselves for the next 17 years until it is time to emerge again.
There are various cicada broods, of which Brood X is by far the largest. They were assigned roman numerals based on their year of emergence and their location. Broods I to XVII are 17-year cicadas, while XVIII to XXX follow a different, 13-year cycle. No one is entirely sure why the cicadas have evolved this periodic lifecycle, although it is thought likely to be as a defense against predators. Few predators live long enough to remember a previous emergence, and by emerging in such massive
numbers the cicadas overwhelm anything that might prey on them: no matter how many get eaten, there are still millions left to breed. They do, though, get infected by the parasitic fungus Massospora cicadina that has evolved to match the cicada cycles. This affects only the males, making their abdomen and genitalia fall off, but it also makes them exceedingly sexcrazed, so that they spread the fungus. It even causes males to make female wing clicks, attracting other males who then try and mate with them. However, it only ever manages to spread through about five per cent of any emergence before the mass die-off. Infected insects are reputed to be prized by people who claim they get an amphetamine-like high from consuming them. Others view uninfected cicadas as a delicacy and eat them – apparently, they taste like tinned asparagus. BBC News, 17 May; Guardian, 26 May 2021.