Frother Moths: when these moths feel threatened, they secrete a frothy yellow substance that is distasteful to predators
Moths of the genus Amerila are commonly known as frother moths, because they're able to produce a frothy, foul-tasting substance that helps to deter predators. The fluid is secreted by the prothoracic glands, which are located near the base of each wing, and a distinctive "sizzling" or "hissing" sound is often emitted as the frothy substance bubbles out.
As this article explains:
If molested, resting adults produce quantities of a frothy, orange fluid from their prothoracic glands, accompanied by a sizzling sound. The froth not only has an aversive odor to humans but also contains PAs (pyrrolozidine alkaloids) which are likely taste-repelling.
Above: Amerila crokeri and Amerila rubripes
The adult moths of this genus are pharmacophagous, which means that they acquire the aversive chemicals that are used to create their froth by ingesting plants that contain toxic or noxious compounds. Those chemicals are then sequestered within the moth's body, where they are repurposed as a defensive secretion.
Above: Amerila crokeri producing its defensive froth
The genus Amerila contains dozens of species, and they are all known to have this defense mechanism. They are widely distributed throughout many different parts of the world; depending on the species, they may be found in the Himalayas, Indochina, Southeast Asia, Melanesia, Australia, or Africa.
Metamorphosis Australia: Australian Arctiid Moths
Metamorphosis Australia: Weird and Wonderful Moths
Australian Lepidoptera: Amerila crokeri
Entomo Brasilis: Defensive Froth in Arctiidae Species in the Rio Grande do Sul State, Brazil (PDF)
Moths of Australia: Adult Adaptations for Survival
Neotropical Entomology: A Fieldwork-Oriented Review and Guide to PA-Pharmacophagy
