Of the beetle intruders Harpalus rufipes is up there with Bradycellus verbascii and Aphodius rufipes in frequency, they appear in droves July onwards and are one of the most common ID requests get for mothtrap beetles.
It even got to a point where I even got a little bit creative with my ID tips and wrote one of the latest raps known to man just to add a little variety...
The golden hair characteristic is a belter, and in the right light it's really obvious even from a distance ( it's most obvious in direct sunlight, but being backlit by an mc bulb also gives the desired affect).
It has its limitations though, this time of year ( end of July) everything starts to look a bit disheveled and hairs fade and become worn off. Sometimes they are stil obvious towards the end of the elytra or sides but do take a bit of investigative work and a 10x handlens to find their traces.
Luckilly theres another slightly less obvious Characteristic you can use: The pronotum, the shape, surface texture and size can help immensely from separating from other similarly sized species in mothtrap (Ophonius ardiosiacus and Curtonotus to name a few).
Shape: The slightly flared bell shape is the first thing you will recognise and instantly rules out some of the larger Ophonius which have an evenly curved pronotum edle with curved hind angles ( they are sharp, almost right angles in H.rufipes).
Texture: H.rufipes have extensive punctures on the hind half of the pronotum only, Ophonius are puncture all over the pronotum and are usually very hairy in comparison ( H.rufipes lacks hairs on the pronotum). This rules out the other Ophonus species that have sharp hind angles to their pronotums.
Above:
Extensively punctured pronotum of Ophonus
Keels: Keels are essentially a raised ridge, akin to a 'mountain fold' in origami. Another large ground beetle that comes to light is Curtonotus, but this has 2 very obvious ridges by the hind pronotal corners. H.rufipes lacks these.
Cheeky tip: Curtonotus also have very convex elytral intervals, giving their elytra a 'distinct corrugated metal sheet appearance' compared to the somewhat flatter intervals of H. Rufipes.
Hope that helps
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