New research appears to provide a long-sought answer about the mysterious cicadas that emerge after years in the ground: do they eat during the brief time they spend as adults before dying? The study found evidence of plant DNA in the guts of some adult cicadas, but not in the guts of those that freshly reached the surface, seemingly confirming that these cicadas will take time out of their packed schedules to grab a bite.
Cicadas are a broad group of sap-eating insects found throughout the world. As part of their life cycle, cicadas will generally spend most of their time as nymphs living and feeding underground before emerging above the surface as mature adults. This underground phase typically lasts two or more years, but can vary between populations and isn’t synchronized for most species. This means that most species will always have some number of cicadas appear annually.
But in North America, there are several species in the Magicicada genus that have much longer and tightly coordinated life cycles. These periodical cicadas, as they’re known, will rise en masse from the ground every 13 or 17 years. They’ll then spend the precious next two to six weeks as adults, hoping to mate and give rise to the next generation of eggs that will hatch and burrow themselves into the ground, starting the lengthy process over again. These cicadas are classified by specific broods, based on their scheduled period of emergence, though broods will be made up of several species.
The spectacle and precise timing of these events has made them a popular attraction, with two broods expected to arrive next year (there are 15 active broods in total). Unfortunately, the bugs can sometimes be a problem for crop growers, since their egg-laying can damage orchard trees, especially younger ones.
In hopes of better understanding periodical cicadas, researchers at the USDA’s Agricultural Research Service (ARS) decided to try settling an enduring debate over the nature of their adulthood.
“Despite a tentative scientific consensus to the contrary, the perception that adult Magicicada do not feed has persisted among the general public, and recent studies are lacking,” the authors wrote in their paper, published Wednesday in the Journal of Insect Science.
To find out for sure, the team examined cicadas collected during the last emergence of Brood X in 2021 throughout Maryland, Virginia, and West Virginia. They analyzed DNA from nymph, adult, and teneral, or just freshly emerged, cicadas. They found plant DNA in the guts of nymph and adult cicadas, but none in the teneral adults. And since cicadas’ guts are thought to be emptied between the nymph and teneral stage of life, the only reasonable explanation is that adult cicadas truly do munch down once they’re nice and settled above ground.
“Overall, our gut content data corroborate observations of feeding behavior by adult Magicicada spp. and confirm that plant sap is ingested by the adult insect,” they wrote.
The most common DNA isolated from adult cicadas came from woody plants and apple trees. But about half of the adult cicadas tested by the scientists appeared to eat multiple plant species. The researchers theorize that the cicadas feed to replenish their water content and keep their gut microbiome healthy, enough to sustain themselves a bit longer.
There are still many aspects of these cicadas’ fascinating life cycle left to fully explore. And ideally, what we learn about them can help scientists find the best ways for humans and cicadas to cooperate during the brief time we spend together.