What happens when cicadas erupt en masse right into the National Zoo?

Washington, D.C. — The red river hogs are trashing their exhibit.

They’ve torn up the soil around the base of their trees and, when they aren’t sleeping, they’re roaming their yard, noses plunged two inches below the surface of the soil.

Mike Maslanka, head nutritionist at Smithsonian’s National Zoo, in Washington, D.C., has a theory: The African pigs are on the hunt for cicadas. 

The zoo is nestled in Rock Creek Park, a verdant swath of wilderness that bisects Washington. Beneath the zoo, and the park, and the city, lies Brood X, one of the largest populations of periodical cicadas in the world. After 17 years underground, they’re coming up—right into the enclosures of red river hogs, cheetahs, sea otters, American bison, and hundreds of other animals.

The big question for Maslanka and the keepers of the 2,700 animals representing more than 390 species: How will all these residents react?

“Every animal will likely take some interest in them,” Maslanka says of the cicadas. “Whether they eat them a lot, a little, or not at all,” he says, comes down to personal preference.

Big cats and cheetahs are unlikely to make a snack out of them. “They tend not to pay attention to that small stuff,” he says. Herbivores, likewise, won’t eat them.

“If anyone will go to town, my guess is the maned wolves,” he says, explaining that these opportunistic omnivores switch up their diet throughout the year, from plants to insects to small mammals or reptiles.

As we continue our chat on the phone, Maslanka he gets an email from a colleague. “Hot off the presses!” Maslanka announces. It’s a photo of maned wolf droppings—featuring ground-up cicada carcasses. ”The maned wolves have found the cicadas.”

A wild phenomenon

Because the zoo is in a park, wild visitors often show up: deer, squirrels, chipmunks, and migrating birds. Two ravens, the only known pair in the city, occasionally visit the zoo’s resident ravens, Chogan and Iris, says Diana Vogel, an animal keeper in the American Trail section.

But the cicadas are different, if only for their overwhelming numbers—trillions erupting en masse as brown-shelled nymphs, with Washington, D.C., their ground zero. The insects molt their shells, and soft, white bodies become black, winged, red-eyed bugs driven by two urges: eating and mating. 

They take to trees, where they feast on sap, and the males sing in unison—an all-enveloping trilling—to attract females. They mate, and the females lay eggs in tree branches. In time, nymphs hatch and fall to the ground, where they burrow in and lie dormant for another 17 years. The entire cycle lasts about six weeks. (Related: Listen to the elaborate cicada choruses.)

Maslanka started working at the National Zoo 15 years ago, two years after Brood X last emerged, in 2004. “We’ve heard stories from the old timers of scooping [cicadas] off Olmstead with shovels,” he says, referring to Olmstead Walk, the main pedestrian path that winds through the zoo.

Across the city, “you couldn’t walk because they were crunching. People’s lawns just shivered. And the only thing I could hear were cicadas and blackpoll warblers,” says Dan Rauch, a wildlife biologist at the D.C. Department of Energy and Environment.

Rauch says he’s eager to see how wild creatures—including the blackpoll warblers, which are passing through the city on their spring migration from South America to their Canadian summer breeding grounds—react.

“The data set is small because we’re talking every 17 years,” Rauch says. “But I really want to see which species utilize the cicadas. It’s all a big science experiment.”

The cicadas’ appearance could cause a population bump of native animals such as blue jays, robins, raccoons, and opossums. If food is scarce in the spring, not all young survive, “but here,” he says, “there should be food crawling or walking or flying right in front of them.” And such easy access to food won’t affect the young animals’ ability to develop foraging techniques. “It’s more like a bonus,” Rauch says.

With the zoo animals, quantity is a concern.

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“If they eat a couple dozen, I’m not terribly worried,” Maslanka says. “Eat a couple hundred, and we could have some problems.”

Cicadas are full of protein and fat, he says, but their outer skin and wings, or exoskeleton, consist of chitin. This hard, keratin-like material can be difficult to digest, especially in large quantities.

Keepers monitor animals’ weight and behavior and can adjust their diets if they’re gorging on cicadas. Maslanka says his team plans to test cicada nymphs for their nutritional and energy value.

“If this was normal times, and we had access to volunteers, we would probably think about setting people in front of some exhibits to watch consumption,” he says. The zoo has been closed to visitors and volunteers since November because of the pandemic, and it’s only now starting to resume normal operations.

Cicada hunting

At the zoo last Friday morning, the first day of its reopening, I smelled the maned wolves before I saw them—their urine emits a potent, skunk-like aroma, helpful for marking their territory in the wild. As I got closer, I spotted one of the South American carnivores—it looked like a lanky red fox—digging frantically in the grassy tussocks of its habitat. Territorial as it may be, this wolf had some visitors it didn’t mind a bit—it was gobbling up what could only be cicadas.

In their domain down the path, the red river hogs Maslanka had seen trashing their yard were sleeping lazily, perhaps in a cicada-induced coma.

I met keeper Diana Vogel on the American Trail. She was holding a bucket of cicadas gathered from the beavers’ habitat. (The plant-eating beavers couldn’t care less.) She’d added some leafy sticks for the insects to roost on. “I’m a zookeeper, so I gave them enrichment!” she said, laughing.

As we walked, she tossed a couple of cicadas into the ruddy ducks’ pond. They hustled over and scarfed them up. We continued past the ravens’ enclosure, and Vogel mentioned that Chogan and Iris had been digging a lot more than usual. They’ve probably found cicada nymphs, she said.

When we got to the river otter habitat, Emmet and Potomac, father and son, were doing somersaults in the pond. Vogel put a few toys in their area, including an otter-size mesh lounger, and plopped some cicadas down too. The otters rushed over to the insects and started batting them around, stunning them. The otters stretched out on the lounger, played with the cicadas some more, then polished off the disfigured bodies.

It’s not always easy being a cicada

After spending 17 years peacefully eating tree root sap underground, life for cicadas aboveground in the city can seem brutal. Some hobble along with torn wings, mangled legs, even missing part of their torsos. Some become bird food; others, otters’ playthings. They litter the pavement, dead, like fallen leaves.

It doesn’t matter—they’re meant to die en masse. The strength of the brood lies not in individuals but in its collective force of numbers. No matter how many cicadas red river hogs feast on or car tires squash, enough of Brood X will survive to mate, lay eggs, and spawn the next generation. If our ecosystem stays favorable for them, we’ll meet their babies in 2038.

For Rauch and Maslanka, scientists, this turn for the cicadas is plenty exciting. It’s “super cool as long as everyone behaves themselves,” Maslanka says, meaning the zoo animals.

The cheetahs, at least, were keeping their cool. Lazing on a grassy slope, indifferent to their surroundings, they appeared oblivious to any cicada interlopers. In front of their exhibit, backs turned to the cats, two toddlers crouched over a cicada on the path, transfixed by the black bug at their feet. 

“We can see those at home in our backyard,” their mom said, trying to get their attention. “Look at the cheetahs!”