I have recently encountered Triple-spotted Clay for the 1st time on 15th June, when this very tatty individual turned up. I submitted it to the VC30 Moth recorders who confirmed my suspicions. This made me think of a few individuals I had last year that were very good candidates for Triple-spotted Clays. On 25th June another likely turned up, so I did a bit of fairly unscientific detective work trying to look for the subtle distinguishing features. This specimen is also in the hands of the recorders. All photos below feature Double Square-spot on the left and Triple-spotted Clay on the right. The specimen was finally Gen detted in 2014 and was indeed a male Triple-spotted Clay.
As I said before the differences seem to be very subtle as colours, patterns and size vary considerably. Some of the Double-Square-spot I've seen are quite dark, others a pale grey. It seems that even when weighing up all of the 'differences', only 'classic' looking specimens will be identifiable. So any wear or variable features outside the norm seems to make it almost impossible to tell without genitalia examination.
To me, wing shape is the most diagnostic feature before any further investigation. In Triple-spotted Clay, moths look very straight sided, with next to no wedged effect. The purple tinge on this particular specimen had an almost iridescent quality making it stand out from the rest. Overall the Double Square-spot looks heavier and slightly more angular, especially the thorax.
After you have your likely candidate, examination of the upper side of the hind wing is next. The picture again shows the subtle difference. In some parts of the country Triple-spotted Clays are much darker, but so far I have only caught 3 and they have been lighter ones. To put it into context, in the same time period I have caught 46 Double Square-spots.
This close up of the head/thorax shows the broader more angular look of the Double Square-spot. The tufts seem to be much more exaggerated, as well a contrasting with the grey central area of the thorax.
It seems that in Bedfordshire (VC30) at least, Triple-spotted Clay seems to be generally much paler and therefore very similar to the much more frequently encountered Double Square-spot. Our own recorders also trap on regular holidays in North Wales and find that the former is often very dark and easily distinguishable. I hope this post has been helpful in some way, but as stated before, is far from scientific. Its really just my own personal musings............
