Archivos de diario de septiembre 2024

03 de septiembre de 2024

Short term scale wear on a moth

As all of us do sometimes, Jack (@jcochran706) photographed the same moth at different times on the same evening and inadvertently (?) uploaded the images as separate observations. His original uploads of two crisp images of the Texas endemic Capps’ Petrophila can be seen here and here. Here are medium-sized versions of each image:

The two images were taken about 25 minutes apart and the moth had evidently moved from one perch to another. (Jack indicated he had two moth setups that night and couldn’t tell me on which each image was captured…but that’s beside the point.)

What first drew my attention to the possible duplicate offerings was the wear on the face of this individual moth—the creamy white scales on the face of the moth are absent in both images. I enlarged each of Jack’s sharply focused images to examine them carefully to verify my suspicion. From the wear on the head and thorax it was easy to discern that both photos showed the same, slightly worn moth.

The two images both show the moth in a relatively similar posture, which allowed me to examine each further in excruciating detail*. Based on this exceptional opportunity, I quickly went down a rabbit hole of examining minute details of the wing patterns. Many Petrophila species have a forewing pattern of a pale ground color liberally sprinkled with tiny black or dark brown dots—often single black scales. In the present instance, I began looking carefully at the set of black dots in the basal third of the forewings. And—no surprise—the two images showed some scale loss from the earlier photograph to the later one. But keep in mind, this scale wear happened in only 25 minutes!

P cappsi wing comparison jcochran706 edits

Scale Loss in 25 Minutes

Above is a side by side comparison of a closely cropped portion of the base of the left forewing of this moth. The earlier image (10:53 PM CDT) is on your left; the later image (11:18 PM CDT) is on the right. I have highlighted a few of the changes that I can recognize. The four numbered red arrows point to black dots that are present in the earlier photo and absent later. I interpret these as scale loss. I’m sure a careful examination of the entirety of the wings would show more. It’s just easy to spot when black dots are missing on a white background. The wing itself, under the scales, is a pale translucent membrane. It would be hard to spot missing white scales for that reason.

Jack pointed out something else which is apparently further scale loss: Notice the dark area in the oval in the upper right of each image. These are NOT areas of dark scales; this is an area of the dark integument of the moth’s thorax showing through between gaps in the white scales of the thorax and adjacent scale tracts. In this case, the loss of some white scales exposed a little more of the dark thorax underneath.

Can Moth Scales Wiggle or Move?

I normally think of the scales on a moth or butterfly wing as being fixed in position, like overlapping shingles on a roof. But I was puzzled by some additional details that I recognized in the two images above. Notice the dark dots I’ve highlighted by a “?” and black arrows, and compare these to their apparent positions in the later image. Each of these (and perhaps a few more) seem to have shifted laterally just a little bit to the right between the two time marks. IF each represents a dot that is about a single scale wide, the shift looks to be about 1 to 2 scale-widths to the right. I would hope that this isn’t happening with my roof shingles. So what does this represent? It seems that the scales are not fixed in place like the roof analogy. My best guess is that the black dots actually show only the tip of a wing scale; the basal part of the scale attached to the wing is hidden some distance underneath the overlapping scales above it. This might make them behave more like a bird’s feathers which can rearrange (or be rearranged, in the case of the bird) somewhat. Is there anyone out there who is more familiar with the micro-structure of Lepidopteran scales who might shed some light on this apparent scale movement?

Conclusions

Moths lose scales over time. The wing wear on “older” moths is apparent to anyone who looks at lots of these. But we typically lack any time scale on this scale loss. In the uncommon instances when a moth is photographed from one night to the next, or from one evening to the next morning, wear may or may not be evident. In the present instance, a small amount of scale loss is evident in just a 25-minute span of time.

Another point may be apparent: It takes exceptionally detailed and close-up photography to approach questions like those above. My thanks and congrats to Jack for—time and time again—offering up such beautiful natural history imagery which makes such an investigation possible!

(* As a side note, for several years now I have been examining hundreds of images of Two-banded and Capps’ Petrophila in Texas attempting to find ways to distinguish the two species when views of the diagnostic hindwing patterns were not evident. So far I have failed in that task. Much to his credit, Jack is not only the most prolific documenter of the endemic Capps’ Petrophila, but his photography is of such high quality that it allows me chase such arcane questions.)

Publicado el septiembre 3, 2024 09:57 TARDE por gcwarbler gcwarbler | 3 comentarios | Deja un comentario

Cross-referencing a post on Moths of Greater Austin

For anyone who might be interested, I just posted an article in the journal for the Moths of Greater Austin Project addressing "Short Term Scale Wear on a Moth". This brief investigation was based on, and made possible by, the great photography of @jcochran706 regarding a couple of images of the Texas endemic Capps' Petrophila.

Enjoy!

Publicado el septiembre 3, 2024 11:32 TARDE por gcwarbler gcwarbler | 0 comentarios | Deja un comentario

04 de septiembre de 2024

Cross-referencing a journal post on Moths of Greater Austin

For anyone who might be interested, I just posted an article in the journal for the Moths of Greater Austin Project addressing "Short Term Scale Wear on a Moth". This brief investigation was based on, and made possible by, the great photography of @jcochran706 regarding a couple of images of the Texas endemic Capps' Petrophila.

Enjoy!

Publicado el septiembre 4, 2024 12:46 MAÑANA por gcwarbler gcwarbler | 0 comentarios | Deja un comentario

06 de septiembre de 2024

Macaria grossbecki at Bentsen-Rio Grande Valley SP

On September 5, 2024, Bianca J. Banda (@biancajbanda) uploaded an observation of an unidentified Geometrid moth from Bentsen-Rio Grande Valley State Park. After wandering through the Moth Photographers' Group site and consulting Ferguson's 2008 MONA fascicle on the family, I identified the moth as Macaria [syn. Speranza] grossbecki, a very rare moth originally described in 1913 by Barnes & McDunnough from Brownsville and San Benito, Texas. Ferguson writes that "although [the species] was described from 19 specimens, few have since been collected". He had seen only two other specimens, one from Brownsville collected in 1928 and another from Santa Ana NWR in 1970. Here is Bianca's image of the species:

Bianca's image represents the First Known Photograph of a Living Specimen of the species.

The species can be recognized by the following combination of details:

-- Forewings whitish rather than gray, buff, or yellowish as in most other members of this subfamily.
-- Slightly wavy, nearly complete PM line which is heavily shaded on the inner 2/3, often showing two more prominent areas of thickening. A narrow AM line can be present or absent.
-- Two to four black subapical spots beyond the PM line. On Bianca's image, the right FW shows two such spots, one just below the subapical black mark on the costal margin and a smaller one at about the midway point and just beyond the shaded PM line. Images on MPG show 3 to 4 black spots lined up in this area.
-- A small black discal dot is usually present.
-- The fringe is mostly dark gray.

This species is most easily confused with the Frederickia cyda/s-signata complex, but those species have a much more sinuous (wavy) PM line, lack the subapical spots, usually lack a discal dot, and have a paler gray fringe that doesn't contrast with the ground color of the FW. Here are a few examples of this species complex:


Frederickia s-signata complex: (L) Falcon SP (Starr Co.); (mid) Balcones Canyonlands NWR (Travis Co.); (R) Timberlake Bio. Station (Mills Co.). All ph. by the author.

Thus far, the small set of records of Macaria grossbecki are confined to Cameron and Hidalgo Counties in the Lower Rio Grande Valley. I went through several hundred unidentified (and under-identified) Macariini across much of South Texas yesterday and found no other images of this species.

Congrats and many thanks to @biancajbanda for her efforts, attentiveness, and enthusiasm to document the wildlife of Bentsen-Rio Grande Valley SP!

Publicado el septiembre 6, 2024 03:34 TARDE por gcwarbler gcwarbler | 6 comentarios | Deja un comentario

29 de septiembre de 2024

Missing or Overlooked Larvae?

The lichen genus Eudesmia consists of at least 14 species ranging from the southwestern U.S. and Central America to southern South America. The genus is most diverse from Mexico to Colombia. The adults are readily recognized as a group by their common color scheme and pattern:

Interestingly, the larvae of at least one widespread species, Eudesmia menea--and perhaps others--are also readily recognized:

So much so that a significant proportion of all iNat observations of this genus in Central America pertain to these bristly larvae (not unlike the situation with the familiar Fall Webworm Moth and the Salt Marsh Moth of North America). I just did a quick tally of such observations for Eudesmia and, even allowing for some misidentifications, I found that about 45% of all iNat observations of this genus from Guatemala south through Colombia (approaching 900 observations) involve pictures of the bristly larvae.

The northernmost species in the genus, Eudesmia arida, ranges from the southwestern U.S. (Texas to Arizona) south through the arid highlands of Central Mexico. Here's a panel of images of this species from a previous journal article of mine, showing the wide variation in the colors and patterns of the adults of this species:
Eudesmia arida comparison
To date, there are over 275 observations of this species. And yet, there is not a single image of an identified larva of this species on iNaturalist. This discrepancy is very surprising. I suspect that if the larvae of Eudesmia arida were anywhere near as conspicuous as those of its congener, Eudesmia menea, observers in the region would long ago have encountered and documented them in numbers. Since that is not the case, I must assume the larvae are much less recognizable--perhaps cryptic, misidentified, or even undescribed.

This offers a challenge to delve back into the literature on the Arid Eudesmia, see if the larvae have been described, and then search through the masses of unidentified iNat larval observations in the range of that species to seek them out. This isn't high on my priority Do List at the moment. Anyone want to take this on?


Details on the above images: Adults (L to R): Eudesmia arida, Texas @ddcurrie; Eudesmia menea mated pair, Mexico, @silvanolg; Eudesmia lunaris, Colombia, @smejiadu
Larvae, all Eudesmia menea: (L) Mexico, @patricia_maya; (middle) Mexico, @jcruzmendoza; (R) Honduras, @gabrielazelaya
For the array of Eudesmia arida images, see my journal article from November 2022.

Publicado el septiembre 29, 2024 04:00 MAÑANA por gcwarbler gcwarbler | 0 comentarios | Deja un comentario