Found this on a door at a customer's house.
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I think this is a comon Plume Moth.
I'm a student so be gentle.
I agree, this is almost certainly Emmelina monodactyla, the only small element of doubt arising because a few years ago it was discovered that there is a second species of Emmelina found in Britain, and it is only distinguishable by dissection. However, so far this second species has only been found in the Wicken Fen wetlands area, so would be very surprising if it turned up on a door in Truro!
Entomologist and biological recorder
Almost certainly Emmelina monodactlya but it will require dissection to formally eliminate Emmelina argoteles.
David is of course technically correct that we can't be 100% sure of the species without disecting it, but personally I think we can be 99.9% sure based on current British evidence. Emmelina argoteles has only been recorded from Wicken Fen so far in Britain, where it was first discovered in 2005, and it is believed to be associated with damp fen and marsh habitats. The likelihood of it turning up in a built-up area on the other side of the country must be very small.
Of course, if further populations of E. argoteles are discovered away from Wicken Fen then this identification, plus many others, will have to be re-assessed, but for now my own feeling is that all moths that look like E. monodactyla, and are not in wetland habitats, can safely be counted as E. monodactyla.
Lat/Lng: 50.268372746443, -5.0405788421631
OS grid ref: SW834453