#the frothy pom pom defense

[artifacts-and-arthropods]

Frother Moths (Genus Amerila): when these moths feel threatened, they secrete a frothy yellow substance from the glands on their thorax, producing chemicals that are distasteful to predators

Above: Amerila astreus

Moths of the genus Amerila are commonly known as "frother moths," because they can produce a pungent, unpalatable froth in order to deter predators. A distinctive "sizzling" or "hissing" sound is also emitted as the frothy substance bubbles out.

Above: Amerila crokeri, commonly known as Croker's frother moth (top), and Amerila rubripes, also known as Walker's frother moth (bottom)

The substance, which has a bright yellow or orange appearance, is secreted from the prothoracic glands located near the base of each wing, just behind the moth's eyes.

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. This phenomenon applies to all the Amerila and has been recorded from other Arctiids including Creatonotos.

Above: close-up of Amerila crokeri secreting its bright yellow froth

The adult moths are pharmacophagous, obtaining the aversive chemicals that are used to create their froth by ingesting plants that contain toxic/noxious compounds. Those compounds are then sequestered within the moth's body, where they are repurposed as a defensive secretion.

Above: Amerila astreus

The genus Amerila contains dozens of documented species, all of which are known to possess this defense mechanism. They are widely distributed throughout many different parts of the world; depending on the species, they can be found in the Himalayas, Indochina, Southeast Asia, Melanesia, Australia, or Central/Southern Africa.

Above: Amerila crokeri

Sources & More Info:

Metamorphosis Australia: The 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

Advances in Insect Chemical Ecology: The Curious Relationship Between Tiger Moths and Plants Containing Pyrrolozidine Alkaloids (PDF)

Neotropical Entomology: A Fieldwork-Oriented Review and Guide to PA-Pharmacophagy