If you spend any time outdoors, you’ve seen something like this on plants. Maybe you thought, “gross,” and walked away. But if you’re 8 years old, or a scientist interested in how insects breathe, you might have looked inside and seen a spittlebug. That’s the nymph or young form of an insect called a froghopper. It’s a relative of aphids and cicadas. But why the spittle? One idea was that it served as protection. Another was that it somehow helped the nymphs breathe, like bubbles of air that diving bugs use. It wasn’t hard for the researchers to find the bugs to bring back to the laboratory, or to watch how they make the foam. Here’s how it works. A spittle bug sucks up watery sap from plants. As it excretes urine, it forms the bubbles. The sap is not that nutritious, so the bug drinks a lot. Consequently, it excretes a lot of urine, about 150 to 280 times its body mass every day. That would be about 2,700 gallons for an average-sized human. The foam creates a kind of cocoon for the young insect to grow, as well as offering protection from birds, wasps and spiders. It has kind of a bitter taste. But the question for scientists was: Does the nymph breathe through those bubbles? No, not usually. The bug sticks the tip of its abdomen up out of the foam as a kind of snorkel. You can see it just breaking the surface. Measurements of carbon dioxide in the bug’s environment and oxygen in the bubbles show that it is breathing while it’s snorkeling. However, if it’s threatened, it sinks down in the bubbles. It doesn’t stay there long unless it has to. Then, it pops smaller bubbles to form a larger one that it can breathe though, like an emergency air supply. Then, once the coast is clear, the spittle bug can re-emerge. Eventually, the nymph forms one big bubble, hides inside it and undergoes a transformation to its adult form. But without its bubble home, what does it do about predators? Well, it’s a froghopper. It hops. Boy, does it hop.