Thursday 2 October 2014


After Ina's request, here's an attempt at showing you the various parts of the male genitalia, used for identifying species. I've annotated a moth identified today as Bryotropha similis, which is another county first for Ceredigion, along with politella the other day. Now politella is a much more exotic looking moth (I refer to its private parts), but see if you can find the equivalent parts from the notes and names on similis. Similis was found at Ynys-hir.
Key: Aedeagus is the phallus of the male
Thorn shield: this is one of the diagnostics and is a number of spikes comprising what is termed a thorn-shield. In similis it is supposed to be up to 100, although here it is over 100.
Gnathos: This supports the anal tube and its shape is another diagnostic
Sacculus: this forms the base of the valvae, which in themselves are 2 wing-like structures.
Vinculum: In Bryotrohas these often have a knee-cap shape and the lack of one in similis is another identifying feature

So to id it as similis, I counted the number of spikes in the thorn-shield, looked at the shape of the gnathos - in this case sharply bent and wider after the bend tapering to a point, the lack of a knee on the vinculum and finally the wing pattern of the adult moth. I used the key in MBGBI volume 4(2) plus an additional publication called The Genus Bryotropha in the Western Palearctic by Karsholt & Rutten.

The first image shows the parts with names, the second is the recent politella of Liz and the third, to help, is another politella from another county but in a shape that is similar to the similis, so it might be easier to relate them all.

Why are some backgrounds blue and others fawn? I choose what to make the background in the complex process of photographing microscopic parts and in some cases I feel that pale blue accentuates the features and in others fawn does the same. Rarely I will use a pale yellow.

Bryotropha similis Ynys-hir - Ina Smith
Bryotropa politella - Liz Snell
Bryotropha politella - from Bucks with aedeagus separated

Peter Hall


  1. Well, thanks for that Peter....I think!! Not all smoke and mirrors then?
    Seriously, it helps clarify what you have to look for to determine a moth to a species.

  2. Many thanks Peter. Very interesting. I have been trying for some time to get an explanation of the 'parts' that in any way relate to human anatomy. I think I am a little further forward!

  3. Bryotrophas' bits present differently to most others in that they are photographed from the side. For almost all others they are opened up and viewed from the top as it were, but then Gelechids parts are often very different to other groups. I'll repeat the exercise if I get an interesting one from another family. Identifying Bryotrophas can be very tricky. The similis I double checked with one of the national experts - Martin Corley - before letting Ina know.

  4. Thanks Peter. Really clear pics. I am struggling to understand how you can extract these parts without damage from such a tiny creature.


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