Had lots of encounters with Scathophaga calida in the Hebrides this summer where it sometimes outnumbers S. litorea. Was just adding some additonal photos to my Flickr site last night (and comparing the material I had to hand) which allowed me to critically compare my Hebridean material (that is the clearly the same as Skye material from Jon Cole at OUM) with some Shetland material sent to me by Roger Thomason a few years ago (also featured in the Diptera.info gallery as photos of living flies). Calida has always been regarded as a really variable species but I'm not sure that the Hebridean and Shetland material are the same taxa. The Shetland material is much darker in both sexes esp legs, frons, antennae) and the males have noticeably long-hairs on the legs and abdomen - super-furry as opposed to just furry, plus the body shape is a little diffferent. There are further boreal coastal Scathophaga species, and some of these are covered in a key by Sifner (2018) but it is not a very easy key to intepret. I've attached images of a male of each form here, and there are many more photos of both sexes of both forms (with details of body parts) on my Flickr site here: https://www.flickr.com/photos/63075200@N07/sets/72157719245700362/.I've posted a message on Diptera.info but if anybody has any material of calida, can you check it to see if you can find either one of the two forms, or more critically any intermediates. Also, if anybody has any expereince of non-British coastal Scathophaga species and thinks they ay be able to assist, drop me a line (falkentomology(at)gmail.com).
PS, see the complete Flickr Scathophagid gallery here: https://www.flickr.com/photos/63075200@N07/collections/72157719233655433/