Inside the spittlebug’s bubble home
White foam that looks a bit like frothy spit is a familiar sight to gardeners. That foam is sometimes called cuckoo spit, because, like the call of the cuckoo, it is a sign of spring. Inside is the nymphal form of a familiar leaping insect, the frog hopper.
The nymphs, called spittlebugs, make the foam by emitting air from their abdomen into their copious and watery urine, mixed with some sticky fluid to aid in bubble formation.
“They’re really more piddlebugs than spittlebugs,” said Philip G.D. Matthews, a researcher in the zoology department at the University of British Columbia, who published a report on how spittlebugs manage to breathe in that nest of bubbles.
Matthews’ specialty is the various ways insects get oxygen from their environment.
It was seeing the foam nests that prompted 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. But that did not turn out to be the case, except in extreme situations, as he reported in The Journal of Experimental Biology.
Matthews and two students, Kephra I.S. Beckett and Anne B. Robertson, captured easily found spittlebugs, which showed no signs of distress in captivity.
They could watch the bugs and record their oxygen use and production of carbon dioxide. Insects do not 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.
When the spittlebugs were scared, they retreated deeper into the safety of the foam and stopped breathing.
When the researchers forcibly kept the spittlebugs under the surface of the foam, the insects were able to break the bubbles to get oxygen. But it was a method of last resort.