Approx. 1cm in length. Found near a pond, which would fit with reed beetle habitat.
No interactions present.
I have been told that, apart from general body shape, Donacia and Plateumaris are distinguished by the form of the elytral suture and by the presence of a spine on the rear femur in Plateumaris. [iSpot Search: Stockway Donacia sp? (cont.).]
There is an image of the spine (thorn-like tooth) at a site: Dave Hubble’s ecology spot: Jewels in the reeds. The image (No. 4) was taken from the side; so I think a part answer is that your image doesn’t show this particular feature but that this is something that could help dictate camera angle in the future. Dave Hubble thought (on balance) that his Image 2 was of a Donacia species.
That's interesting to know; definitely something to bear in mind next time I encounter one of these species.
Lat/Lng: 51.2, 0.1
OS grid ref: TQ4949