It was seeing the foam nests that prompted Dr. Matthews to study the insects. “It got me wondering exactly how would a spittlebug be able to breathe if it was submerged” in a mass of bubbles,” he said. One possibility was that it drew oxygen from the bubbles, like a diving insect. But that didn’t turn out to be the case, except in extreme situations, as he reported in The Journal of Experimental Biology.

Dr. Matthews and two students, Kephra I.S. Beckett and Anne B. Robertson , captured easily found spittlebugs in areas around the university and took them back to the lab. The spittlebugs showed no signs of distress in captivity and continued to go about their usual business, sucking watery sap out of the plants and producing an incredible amount of urine, 150 to 280 times their own body weight every day. For a 150-pound human that would be about 2,700 gallons a day.

They could watch the bugs, observe them under a microscope and record their oxygen use and production of carbon dioxide. Insects don’t have lungs. They breathe through tiny tunnels from exterior holes called spiracles that allow the air to flow through tunnels into their bodies. The spiracles are gathered in a groove that runs to the tip of the abdomen.

Under a microscope, the researchers could see and record the spittlebugs breaking the surface of the foam with the tip of their abdomens, apparently using it like a snorkel. When the insects were doing this snorkeling, carbon dioxide increased in the container they were placed in. That meant they were breathing. The researchers also measured oxygen in the foam itself. Same result.

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When the spittlebugs were scared, they retreated deeper into the safety of the foam and stopped breathing. “When you startle them they pull their abdomen into the foam,” Dr. Matthews said, “and you can see that the rate of carbon dioxide drops to zero, because obviously they’re now hiding within the foam and the gas exchange has stopped with the atmosphere.”