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Cicada Outbreaks Linked to Other Animals' Booms, Busts

John Roach
for National Geographic News
May 30, 2007
 
Periodical cicadas, like the Brood XIII bugs slamming the U.S. Midwest, have an unusual survival strategy: They simply ignore their predators.

"They don't do anything to get away. They don't fly away, they don't try to escape," said John Cooley, an evolutionary biologist at the University of Connecticut in Storrs.

Cicadas emerge in abundance—several million to an acre—so the overall reproductive risk of an individual getting eaten is negligible.

Even the most voracious eaters are unlikely to put a dent in the noisy insect population.

Fortunately for anyone bothered by the horde, adult cicadas die not long after producing eggs. Their offspring quickly disappear underground, not to be seen or heard from again for 17 years.

(Read "Cicada Facts: Understanding the Invasion" [May 21, 2007].)

Today scientists are using this boom-and-bust cycle of periodical cicadas to study the insects' effects on other animals.

What they are finding is that the oft-maligned insects likely play a key role in the life cycles of a variety of other creatures, from moles underground to squirrels in the trees.

Insect Bounty

Just about anything that can eat cicadas gorges on them during their emergence.

Spiders, praying mantises, and ants eat them. Dogs and cats eat them. Birds and fish eat them.

"[Fishing] lure manufacturers have designed cicada-shaped lures to capitalize on this fact," Dan Century, who runs the CicadaMania Web site, commented in an email.

Many humans also eat the low-fat, high-protein insects.

When Cooley and his colleagues were studying the Brood VII emergence in 2001, they heard oral histories about how a cicada diet once got the Onondaga Indian Nation in New York State through times of famine and war.

Keith Clay is a biologist at Indiana University who is studying the effects of the Brood X cicada emergence on moles.

Brood X last made an appearance in the eastern U.S. in 2004.

The burrowing animals eat cicada nymphs, which live underground. The mole population seems to boom in the years just prior to an emergence and crash afterwards.

"There certainly was a lot less evidence of [the moles'] presence and activity [after 2004]," Clay said.

"That is, the mounds and runways in lawns and park areas were extremely common and evident in 2003 and 2004, and now you don't see them."

In addition, he said, the local squirrel population crashed after the Brood X emergence, apparently because the cicadas' egg laying destroyed the nut crop of 2004.

Meanwhile wild turkeys, which feast on adult cicadas on the ground, experienced a population boom in 2005.

"So some interesting patterns—unpredictable patterns sometimes," Clay said.

Cicada researchers are also studying the effect of a fungus on cicada populations. The fungus infects cicadas as they emerge, sterilizing and killing them.

The University of Connecticut's Cooley said the fungus only infects a small percent of the population.

"When you're talking about the numbers of cicadas present, it's so astronomical that it really isn't much of a dent," he said.

Patience, Not Spray

Cooley, who is currently mapping the distribution of Brood XIII as part of a project funded by the National Geographic Society's Committee for Research and Exploration, said people always ask him how to get rid of cicadas.

(National Geographic News is part of the National Geographic Society.)

The only real solution, he tells people, is patience.

"Wait a month; then they won't be around," he advised.

Bags placed around ornamental vegetation and fruit trees prevent damage from females, which lay their eggs in grooves they carve in twigs.

And please, he said, leave the insect repellent at home.

"We try to discourage people from spraying them with bug spray or what have you, because [cicadas are] a natural part of the environment," Cooley said.

"It's not a good thing to remove them, in all likelihood.

"Moreover, to get rid of them, you would have to spray so much bug spray that you'd probably kill everything in sight."

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