When trillions of periodical cicadas emerge in a rare double event, they provide a disruptive feast for other species.
This April, trillions of periodical cicadas began their descent on the midwest and southeast of the United States, causing so much noise that local residents called the police to complain. But the cicadas don’t just disrupt neighbourhoods with a deafening soundtrack, they also throw food chains into chaos.
After spending more than a decade burrowed underground sipping on tree root juices, two broods – Brood XIII and Brood XIX – are emerging at the same time in 2024: the first time they have done so simultaneously since 1803.
Such emergence of the insects en masse will disrupt ecological food systems, says Grace Soltis, a PhD student studying evolutionary biology at Florida State University.
“Cicada emergences can completely rewire a food web,” says Soltis, who co-authored a paper studying the cascading impacts of bird predation on cicadas during the 2021 Brood X emergence. “For predators, these emergences are a huge boom in resources. It’s basically like an all-you-can-eat buffet for the hungry predator.”
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Mass cicada emergences can cover up to 190,000 sq mi (500,000 sq km), says John Lill, professor of biology at George Washington University’s department of biological sciences and another co-author on the cascade paper. As a result, this diet shift causes a ripple effect down the food chain: “It’s a pretty substantial disruption across a whole landscape,” he says, “generalist predators switch over to feeding on this bounty of food”.
I haven’t read the paper, but I don’t think it’s that simple. Having an endless supply of food increases fecundity among predator populations, which means next year there may be a lot more of the animals that eat cicadas than there are this year, but the cicadas will be gone. The question is whether there will be enough food to sustain the increased population size next year, and the answer is probably going to be no.
But isn’t this normal? Predator and prey are rarely in balance.
Population growth cycles are usually pretty stable under typical conditions. It’s hard to overstate the number of cicadas emerging with these two broods aligning this year, this will be a population growth cycle on steroids for predators, which is why it’s remarkable. Next year, with so many additional predators, they will negatively affect the populations of other prey due to increased predation, which will negatively affect predator populations the following year, etc. The point is the population disruptions in these ecological systems will be large
One of the theories as to why these periodical cicadas evolved these lengthy reproductive cycles is because they avoid elevating predator populations long-term.
Mongol invasion happened to coincide with a period of mild winters in Mongolia. That weird moment when you and all your neighbors have fifty horses and you’re left wondering what now?