Moth Identification Using Named Features.

[melbellingham]

I have often struggled with some of the features mentioned in the ID guides that I have, and have need to reach for one of them to remind me of a named feature.

An example has cropped up on the forum recently when a particular feature was mentioned.

In ‘British Pyralid Moths’ by Barry Goater, he describes a feature that differentiates between Agriphila selasella and A. tristella. The feature ‘a distinct facial cone’ is missing on A. selasella but can be found on A. tristella. The feature is not illustrated as the images are life size set specimens.

I never really understood what was being described and because a similar description (facial cone) was found on the internet (see below), I probably misunderstood the feature entirely.

NB. I am not suggesting that this is wrong, but merely using it as an illustration of how I became confused.

A post by JohnR (Some help needed with unknown micros) on Sept 21, included an image of Agriphila selasella. The ID was made by SteveHH (who better) and was determined because ‘it lacks the cone above the eye which is present on Agriphila tristella’.

I have looked back through some of my images of A. tristella but cannot convince myself that I know what I am looking for.

If Steve reads this post, would he please explain to me (and possibly others) what I should be looking for.

Mel.

[GasMacc1]

Excellent question, Mel. I'm not sure. I've had a few attempts at understanding this in the last couple of years, so will review any notes I can find, in case it throws any light on the subject. I'm fairly certain that the arrow (labelled "9") in the diagram, is not pointing accurately to the cone!

(Unless "facial cone" is different from "eye cone", which is one of the features that I thought separated A. tristella and A. selasella).

[GasMacc1]

I remember seeing a comparison on lepiforum.de, so I've copied the pictures below.

They seem to illustrate that the "forehead" (sorry, I can't find the technically correct name!) of Agriphila tristella is pointed, whereas that of Agriphila selasella is round.

A. tristella. Pointed feature (scales removed)

A. selasella. Rounded feature (scales removed)

The direct comparison shows this clearly, but - as the annotation "Stirnschuppen entfernt" indicates - the scales on the "forehead" have been removed.

A picture of A. tristella with the "Stirnschuppen" intact hints that it might not be so obvious to spot the difference with the scales on.

A. tristella (scales intact)

[GasMacc1]

Here's a close-up of the relevant area of the A. selasella moth, from the photo taken by JohnR.

A. selasella (cropped from photo by John R)

[GasMacc1]

In 2018, I posted a photo of A. selasella, which Steve Hind confirmed with these words:

"Agriphila selasella ... has a gently curving rim around the upper edge of the eye to the front of the face, which is clearer in your ... photo. In A. tristella the face has an upward projecting cone above the eyes and before the long palps".

Here's the photo of the A. selasella followed by a close-up of the relevant area.

Agriphila selasella (Dave Maddy 2018)

A. selasella - close up of eye cone (Dave Maddy 2018)

[GasMacc1]

I've chosen a couple of photos from lepiforum, and zoomed in on the head of the moth in both cases.

At a pinch, these might illustrate the "pointy eye cone" for A. tristella and the "round eye cone" for A. selasella.

A. tristella (lepiforum) close-up

A. selasella (lepiforum) close-up

I have to admit, though, I could have chosen other photos from the same gallery, where the feature was not at all clear - in fact, you might have seen round cones on tristella and suspicions of pointy ones on selasella.

Like you, Mel, I'd be grateful if anyone can shed any light on the topic!

[CliveJ]

Another contribution to this discussion.
The annotated images in the post below clarify the distinction between the facial cone and the conical shape made by the labial palps projecting in front of the head, but I think it would require a keen eye (or much faith) to use the feature to distinguish between the two species, certainly on live specimens.

https://britishlepidoptera.weebly.com/a ... tella.html

[melbellingham]

Well then, at least I now understand what I should be looking for.

I have not found any of my images of A.tristella that show any obvious sign of the feature, but until I started looking for images, I hadn’t realised that I had so few, and those I have do not show sufficient clear detail of the head.

I do not have any images of A. selasella, and it is likely that I have never seen one. I know I have never caught one.

Thanks for the comments guys, much appreciated.

Mel.

[melbellingham]

Sorting a few photographs from August earlier today I came across an image of Agriphila tristella that I think shows the facial cone.

It certainly looks right, compared with the images shown on the link provided by Clive to the British Lepidoptera website.

The specimen is showing signs of wear and tear with scales missing, especially on the head, so I would guess that the feature must be more difficult to see on a fresh individual.

Agriphila tristella 07/08/2020

Mel