When is a ctenuchid moth not a ctenuchid moth? When it’s a White-tipped Black Moth (Melanchroia chephise) in the family Geometridae!
I may be a beetle guy, but I also consider myself a competent general entomologist. What is a competent general entomologist? Someone who can identify any insect to order at first glance and a majority of them to family – regardless of one’s own taxa of expertise. Thus, when I encountered this mating pair of moths on the outside wall of my sister-in-law’s condominium in Seminole, Florida, I “recognized” them as something in what I learned as the family Ctenuchidae (later subsumed within the Arctiidae, first as a subfamily and now as several disparate tribes). They had all the hallmarks of ctenuchids—black and red coloration, narrowish wings with light colored patches, and about the size of the wasps that they presumably mimic. Upon my return to St. Louis, I sat down to identify the moths—confident that their distinctive appearance would lead to the quick ID that never materialized after scanning through all of the ctenuchine pages at BugGuide. Frustrated, I resorted to posting the photo on the site’s ID Request, never questioning my ctenuchine placement. Precisely 4 minutes later, the moths were identified by John Maxwell as Melanchroia chephise and moved to their proper place—among the 50 other adult photographs of this species that can be found on the site! I might as well have failed to identify a monarch butterfly!
Melanchroia chephise is apparently common in the American tropics, reaching its northern distributional limit along the coastal plains of Florida and Texas but straying further north in certain years. Larvae feed on several plants in the family Euphorbiaceae, primarily Breynia and Phyllanthus species. The adult coloration strikes me as obviously aposematic (warning coloration), but I could find no specific references to this. However, considering that euphorbiaceous plants are famous for their diverse arsenal of latex and irritant toxins (e.g., diterpene esters, alkaloids, glycosides, ricin-type protein toxins, etc.), it seems reasonable to presume that Melanchroia larvae have evolved mechanisms for sequestering one or more of these compounds. NABA South Texas states that adults of this species are probably mimics of the Red-bordered Pixie (Melanis pixe), an aposematic metalmark butterfly also of Neotropical distribution that reaches south Texas (but not Florida). Personally, I don’t really see the resemblance (but then, nor am I an avian predator). I suppose it’s possible that a species such as this can employ different defense strategies in different parts of its range, relying on Batesian mimicry in areas where suitable models occur and aposematism in areas where they don’t, but I have to admit that I’m now straying well outside the coleopteran-centric bounds of my expertise.
Copyright © Ted C. MacRae 2009