Animals have some wacky ways of protecting themselves from predators, but one bug's defense mechanism is up there with the most ingenious—and grossest.
The European alder spittlebug, a tiny winged insect also known as a "froghopper", farts out a foamy substance that forms a protective jacket, a new paper in the Journal of the Royal Society Interface reveals.
This foam has some weird and wonderful properties, which may even inspire new skin care products.
The bugs create the foam during their nymph phase, which is the stage of development before they reach full adulthood. During this phase, they are vulnerable to being eaten by predators, and the anal foam acts as a sticky trap that protects them from harm.
"Because the foam desiccates as fast as water, predators once captured struggle to free from drying foam, becoming stickier," the authors wrote in the paper. "The present study confirms that adhesion is one of the numerous foam characteristics resulting in multifunctional effects, which promote spittlebugs' survival."
The bugs create this foam from their food, namely xylem sap, a watery fluid used by plants to transport water up and down the stem. Most of this xylem passes through the nymphs' digestive tract, and much of it is used to create the foamy material. The insects use their excrement to form the foam and shoot it out of their anuses.
"The production of the foam is actually a quite complicated process, integrating morphological and behavioral features of the insect," Hannelore Hoch, paper co-author and insect researcher at Berlin's Museum für Naturkunde, told Newsweek. "The foam is created by rhythmical (and to the human eye—rather elegant) abdominal movements— with the abdominal tip alternately dipping into the fluid, and forcing a small bubble out of the channel opening. By this, bubble after bubble appears until the whole body is covered in foam (ca. 15-30 min)."
The foam then coats the outside of the nymph. Interestingly, the authors found that the foam evaporated faster than water, and as it became drier, it became increasingly sticky.
This stickiness is what protects the bugs from predators, as the amount of time that predator insects need to clean themselves of the viscous foam allows the nymphs to escape capture.
"The foam of spittlebug nymphs has several functions: predominant are antipredatory effects—the foam is sticky so that invertebrate predators such a spiders and ants virtually get stuck," Hoch said. "The foam may also protect the spittlebug nymphs from larger, vertebrate predators, such as birds by providing some kind of camouflage or hideaway."
"In laboratory experiments we also observed that the mouthparts of e.g., ants, were rendered non-functional upon contact with foam. The foam also has been shown to have antimicrobial activity, it aids in thermoregulation, protects the insect from desiccation, absorbs light (UV-protection)," Hoch added.
The fact that the nymphs use their own excrement suggests another advantage of this foam: it's energetically less taxing than if they generated it all themselves.
"The sustainable 'reuse' of large amounts of excrement for foam production suggests energetic advantages, also by investing in a thin nymph cuticle protected with the foam. Such a strategy should be evolutionary successful in humid habitats, as confirmed by the independent evolution of foam nests in different groups of organisms, such as spittlebugs, frogs and fishes," said the authors.
The authors hope to further investigate the properties of this weird foam, and delve into whether it could be used in biotechnology or even skin care.
"In our upcoming paper we concluded that adhesion is a key characteristic of the foam. This has ecological implications, accounting for multiple effects for the insects' survival," Hoch said. "Thus, spittlebug foam is regarded a smart, biocompatible material which holds great promise for the development of biomimetic and biomedical applications. Antimicrobial effects, protection against desiccation and light absorption are properties which are critical[...]in dermatology and skin care products."
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