Distinctive long red and black beetle, Paederus genus. Found on a stream bank, on a dock leaf (I think).
No interactions present.
A good example of the differences in the general shape of elytra (dark wing cases) and pronotum (red body section between head and abodomen) can be seen in this pair of pictures: http://www.flickr.com/photos/oldbilluk/4541964308/ and http://www.flickr.com/photos/oldbilluk/4526257525 , given that I can't link to the key I used. Or here - http://www.kerbtier.de/cgi-bin/enFSearch.cgi?Fam=Staphylinidae&Sort=sys&...
From what I read on an Aussie website, these need a health warning attached.
Also mentions dermatitis arising from contact with the haemolymph of some species. News to me - but then there is a mountain of wildlife knowledge I don't have.
The first Paederus species I met were in Africa where they are well known for their toxicity - both the beetle and the irritation they produce are known as "Nairobi eye" - eye problems are common when people rub eyes with fingers covered with the liquid from a squashed beetle. What makes this more likely is that, unlike a nettle rash, it takes a while for the irritation to manifest. However, it is by no means all species that irritate - Wikipedia cites an veterinary study reporting that "at least 20 of the more than 600 species of Paederus beetles have been associated with Paederus dermatitis", so presumably there are plenty that are not. That said, there are also other species in the tribe that are similarly problematic. I'm sure if our UK species were a major problem, we would know. It would have become common knowledge as it is in Africa. This is just a guess, though - I wait to be corrected. In any case, it is only "beetle blood", i.e. a squashed beetle, that is a problem - they don't sting or bite.
I found it fascinating to learn that the beetles do not manufacture the toxin pederin themselves - it's made by a bacteria they host.
Even more interesting when you get to know more. Thanks Sarah.
Lat/Lng: 51.0503, -1.3189
OS grid ref: SU478281
Found on the bank of a channel, River Itchen watermeadows (chalk), on a dock leaf (I think).