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Ever wondered what makes those balls of white foam you sometimes find clinging to plants? Spittlebugs create these bubbly cocoons after feeding on a plant’s fluids; but unfortunately, their eating habits help transmit a deadly bacteria capable of wiping out agriculturally important plants.

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Over half of all insects eat plants, but most of them don't do any real damage. The spittlebug, on the other hand, falls into the minority.

It seems like an innocuous critter, named for the frothy foam it leaves behind. Yet when farmers see this foam, it might throw them into a panic. Because though the bugs themselves aren't that big a deal, they could be a sign of imminent crop doom.

Cercopoidea is a superfamily of bugs containing more than 3000 individual species that can be found all over the world. They're more commonly known as spittlebugs or froghoppers. These little guys usually come in somewhere between the size of a short grain of rice and an unshelled peanut.

But what makes spittlebugs unique — and deadly — is their diet. Spittlebugs feed exclusively on a substance called xylem sap, which is the liquid that moves dissolved nutrients and minerals from the soil through a plant's root system and into the plant. Xylem sap is a little different from phloem sap, which transports sugars produced by photosynthesis.

Luckily for spittlebugs, lots of plants have xylem sap — like, all vascular plants, ones that use a system of vessels to transport nutrients. That's most plants, outside of mosses and a few others. So spittlebugs have options when deciding where to eat out.

When spittlebugs are in their nymph stage, prior to adulthood, they feed on xylem sap by piercing plants with tube-shaped mandibles designed for sucking up liquid. Now unfortunately for them, xylem sap isn't very efficient food, since it's low in nutrients. That means spittlebugs eat a ton — one spittlebug can consume 280 times their own body mass in xylem sap in a twenty-four hour period.

That would be like you eating 19 tons of food every day! Of course, all that delicious sap has to go somewhere. So spittlebug nymphs excrete the excess… anally.

The spittlebug adds some chemicals and then mixes in air. The result is a foamy substance known as cuckoo spit, which spittlebugs use to envelop themselves in a protective, bubbly cocoon that actually looks like spit, but is more like pee. It doesn't have anything to do with the birds, but it does tend to show up in early spring, just like cuckoos do.

It's not bird spit; it's bug pee. Just so we're clear on that. It's cute, if also disgusting, and doesn't seem like it should be that much of a problem.

But spittlebugs are a huge threat to plants. Not on their own, though their feeding can damage plants' overall health. The real reason spittlebugs are actually dangerous is because they can spread a deadly plant bacterium called Xylella fastidiosa.

That sounds a lot like it is a Hogwarts spell, but it causes a very real and very deadly disease in plants. In fact, it's considered one of the most dangerous bacterial infections in plants, and can infect more than 560 plant species worldwide. These bacteria infect a plant's xylem -- which is exactly where the bug's mouthparts are biting.

When a plant becomes infected with Xyella fastidiosa, the bacteria forms colonies that clog up the xylem's channels and block the flow of water and nutrients within the plant. As a result, the plant can't absorb the nutrients it needs, which is definitely not a good thing. Once a plant is infected, its leaves begin to fall off, its growth slows — and if the infection continues unchecked, the plant will die.

These tiny, cuckoo-spit-producing bugs transmit these deadly bacteria from plant to plant as they feed. When a spittlebug drinks from an infected plant, the bacteria colonize its gut. So when the spittlebug moves to the next plant and chows down, it passes along the bacteria, too.

That's bad for plants, of course, but it's also bad for farmers and food production, which can be hard hit by this spittlebug-borne disease. Xylella fastidiosa is the culprit behind a number of illnesses that affect food-producing plants. Unfortunately, there's no cure for the infection, so when it makes its way into crops like grapes, olives, or citrus, the consequences can be dire.

It was 2008 when the first case of one such disease known as olive quick decline syndrome was discovered in the Italian province of Lecce. By 2015, scientists were estimating that 10,000 hectares of Lecce's olive trees had become infected — basically half. In other words, the bacteria had spread to one million olive trees — some of which were over a hundred years old — in less than a decade.

And this disease has stubbornly resisted attempts at eradication. Luckily, researchers are working on developing ways to protect farmland from Xyllela fastidiosa. Like by determining which of the three thousand species of spittlebug are actually responsible for spreading it.

Researchers reported that the meadow spittlebug was the main culprit in spreading the bacteria in Italian olive groves. The scientists discovered that in August 2014, nearly one hundred percent of meadow spittlebugs they collected in Italy's Salento peninsula tested positive for the bacteria. Researchers are also testing other types of prevention and treatment techniques, including chemical sprays that help slow the spread of the disease.

It seems unfair to blame tiny spittlebugs for such a deadly threat. After all, they're just trying to live their best lives, swathed in cocoons of their foam excrement. So maybe with a little more research, we can tackle the real threat and go back to living peacefully alongside these little guys decorating our plants with cuckoo spit.

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