This is a leaf beetle associated with burr-reed. And although I haven’t noticed any burr-reed so far, this pair were on a blade of grass at the spot where I spotted burr-reed last summer. Donacia Simplex is a metallic bronze dimpled beetle, with a quite elongated shape and stripy-looking antennae. It lives on the marginal vegetation of pools and canals, where burr-reed grows, and can be seen from April to August.