Pattern Variation in Eudesmia Lichen Moths

Resumen (español): Describo e ilustro la variación en el tono y el patrón de color que se encuentra en los miembros del género de polillas del liquen Eudesmia.

I recently posted a journal entry describing my "rediscovery" of a species of Eudesmia lichen moth, Eudesmia lunaris, which had been overlooked for over a century. As I mention there, part of the difficulty in identifying moths in this genus deals with their pattern and color variability. I'm still going through thousands of images to sort out additional species which may have been overlooked, but I wanted to take a moment to demonstrate how much variability there can be.

The array below shows examples of Eudesmia arida, the northernmost member of the genus and the only species occurring with any regularity in the United States (Arizona to West Texas). Since no other species in the genus has been documented in this U.S. range, I make the assumption that all the examples uploaded to iNaturalist in the region are, in fact, Eudesmia arida. (I can't make such an assumption further south in the Neotropics.)

Eudesmia arida comparison
Eudesmia arida (all), Upper row: Texas @gcwarbler | Arizona © @finatic | Arizona @psyllidhipster | Arizona @silversea_starsong
Lower row: Arizona @matt_lachiusa | Arizona @court_rae | Arizona © @jaykeller | Arizona @fowlivia

It is apparent when looking at the array of Eudesmia images for just about any species that there is variation in the following aspects:
-- Color hue: Most species show some variation in the color bands and patches from rich golden orange to pale orange, in some cases to deep yellow, pale yellow, or even creamy white color. In Eudesmia arida, most moths have relatively rich orange color patches (above, upper row), but occasional yellow forms are found (lower row). A few species in the genus, especially those in southern South America, tend to be dominated by paler color bands. The amount of color hue variation differs among species and may have regional, seasonal, and sexual components to the variation, but this has not been investigated in any detail.
-- Band widths: One of the most striking aspects is the variation in the width of the orange color bands and smaller details of their shape; note the variation from L to R in each row, above. Certain gross generalizations tend to hold true for each species but the wide variation in these aspects lead several early researchers to name new species based on perceived band-width differences from examination of very few specimens. We benefit now from the wealth of additional images of living examples in repositories such as iNaturalist. Unfortunately, some of the species described in early literature were distinguished also by details of hindwing color pattern (e.g. the width of the marginal black band on the hindwings) and the color of the abdomen, neither of which can be seen in most images of living moths in natural posture. Every image on iNaturalist which shows any hint of the hindwing or abdominal coloration is so valuable for this reason!
-- Size differences: Males of most Eudesmia species are anywhere from 10 to 30% smaller than females (see below). Combined with the variation mentioned above, this probably lead Walker to name the male and female of E. lunaris as different species. The image of a mated pair of Eudesmia ruficollis below, taken by Maria Izabel L. Mosini (@bebelmosini) in São Paulo, Brazil, demonstrates both the size disparity and color differences which can be observed in many species. The differences are not always this dramatic, but it's something to keep in mind.

Eudesmia ruficollis, mated pair, 18 April 2020, São Paulo, Brazil @bebelmosini

My next journal post will deal with the recognition of another distinctive species of Eudesmia found in central Mexico which can apparently be distinguished by some details of head/thorax/abdomen coloration. Stay tuned!

Publicado por gcwarbler gcwarbler, 24 de noviembre de 2022


Tagging some of the folks whose images contributed to this journal entry: @bebelmosini @court_rae @finatic (RIP) @fowlivia @jaykeller @matt_lachiusa @psyllidhipster @silversea_starsong

Publicado por gcwarbler hace 3 días (Marca)

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