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Gloomy Days Ahead
Those aren’t tree zits. They’re an epidemic of tiny tree-sapping insects spread by climate change.

What thrives in urban areas, sports an armored shell, and can cut through tree bark like a samurai’s sword? Teenage Mutant Ninja Turtles? No way, dude. Allow me to introduce to you the gloomy scale insect. This mutant-like sap sipper is native to the American southeast, but it could become more common and deadly as the climate warms. And city trees could suffer mightily for it.

Recent research published in the journal Ecological Applications shows that in areas of Raleigh, North Carolina, experiencing an urban heat island effect, gloomy scale insects can produce 300 percent more offspring than their counterparts in cooler parts of town. (Why Raleigh? North Carolina State University researchers stuck close to home for this study.) At its worst, the heat-related reproductive uptick of the gloomies yielded 200 times as many insects chowing down on a single tree.

Take that image and consider that cities across America are predicted to experience temperature averages climbing 7 to 10 degrees by 2100. According to this infographic by Climate Central, a typical summer day in Raleigh will rise from today’s 88 degrees Fahrenheit to a steamy 97 by the end of the century.

That would bring a lot more bugs. According to the study, a little heat goes a long way for gloomies. Just a difference of two degrees Celsius is enough to show marked increases.

“There are several thousand species in the States alone,” says entomologist Adam Dale, the study’s lead author. “On your houseplants, in your yards, in nurseries, in greenhouses, and on landscape plants. They are just so small and sedentary that most people don't realize they are there.”

Named for its dark, depressing complexion, gloomy scale insects are only about a millimeter long, and they look for all the world like a tiny gray bump—tree acne, if you will. But these blemishes can kill.

When the armored covering is removed from an adult female gloomy scale, the pink, soft-bodied insect is revealed beneath. She spends the majority of her life here, feeding on fluid from within the tree.

After taking a look at 2,700 street trees in Raleigh, Dale found that warmer areas of the city had 70 percent more red maples in poor condition. Urban trees, which often grow in compacted soil or don’t get enough water, can suffer from any number of ailments. But sap-sucking pests further curb tree growth by exacerbating water stress and reducing photosynthesis.

Gloomies start out like regular ol’ insects. Six legs, antennae—you know the drill. Once adults find a nice spot on a red maple limb, though, they tuck in all their appendages and start excreting a waxy, bark-like shield. This little half-shell protects scale insects from the outside world, so they can slurp nutrients out of their host tree like a ninja turtle with a gooey pizza. Life inside is cozy, and the gloomies jettison their legs and antennae, transforming themselves into translucent, predatory pimples.

And like any unsightly rash, gloomy scale infestations just won’t go away. Their tough half-shells can remain intact for more than a century. Entomologist Elsa Youngsteadt, also of North Carolina State University, went to herbariums (think: tree museums) all over the Raleigh area to compare old trees with the region’s temperature records. Her findings coincide with Dale’s: hot weather brings more gloomies.

Youngsteadt says her data provides clues to what could be in store for rural areas as climate change progresses. But none of her country tree samples (either present-day or historical) compare to the high gloomy concentrations Dale found in the city.

City trees are more than decoration. They can play important roles in removing pollution, and urban trees actually scrub more contaminants out of the air per tree than their rural cousins. Some research even shows a correlation between pests killing trees and spikes in cases of cardiovascular and respiratory illnesses. And still other research suggests that trees affect the way humans think, feel, and even heal.

So what do we do to ward off the gloom? Pesticides only work at specific times during this insect’s life cycle. (For instance, when the males regrow their legs and wings during late summer, they leave the protection of their shells to find females.) Biological controls represent other possibilities: Lady beetles, predacious midges, and lacewings all find these tree zits delicious.

Gloomies are no more to blame for their population explosion than the hapless turtles that wandered into a puddle of radioactive ooze. Nor do these bugs represent an apocalyptic threat to human existence. But these tiny, easy-to-miss insects remind us that climate change isn’t just some far-off problem affecting huge polar bears and far-flung Pacific islands. It’s hitting the streets of Raleigh, too.

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image of Jason Bittel
OnEarth news blogger Jason Bittel contributes to Slate and serves up science for picky eaters on his website, Bittel Me This. He lives in Pittsburgh with his wife and two tiny wolves. (Note: wolves may be Pomeranians.) MORE STORIES ➔