摘要：This intricate image of a cicada shedding its skin in the US state of Maryland was taken by Carolyn Kaster. Trillions more will soon emerge across the country for a brooding event that occurs once every 17 years
THIS remarkable image shows just one of the trillions of cicadas starting to emerge in 15 US states after 17 years underground. Carolyn Kaster’s photo captures an adult insect shedding its old skin on the bark of an oak tree in Maryland, before it goes in search of a mate.
More than 3000 cicada species have been described worldwide. Most have a yearly life cycle, but seven species in the US belonging to the Magicicada genus remain underground as nymphs for 13 or 17 years before emerging, a process called periodical brooding. The only other two species of cicada to do this are found in Fiji and India.
This year, insects from a group called Brood X – which is made up of three species – will emerge in the eastern US in their trillions. It is one of 15 broods in the country, and last appeared in 2004 (see photo above). Cicadas from Brood X have already been spotted in Georgia, Maryland and Virginia. After mating, females lay their eggs in the stems of woody plants.
Remaining underground for so long may make it harder for predators to remember where to find the insects, giving the next generation a survival advantage when they eventually emerge.