A substance which acts as a pH indicator from the moth Euchloron megaera

"Wing scales of the moth Euchloron megaera L. (Sphingidae) contain a water-soluble green pigment showing pH indicator properties. This pigment has been isolated. The UV-visible spectra, the color changes, the reduction by dithionite, the polarity on SiO₂ TLC, and the high molecular weight relate this pigment to an anthocyanidin derivative derived from the plant food. This result is discussed in connection with the presence of similar substances in plants of the family Apocynacea and in other moth species of the Sphingidae group, in which they play aposematic roles. As a hypothesis, it is suggested that the green pigment results from a reaction between Nerium sp. anthocyanidins (plant food) and NH₂ groups of basic constituents present in the animal."