These pictures of a male show a small cluster of mites underneath the thorax. Specimens can be seen with far larger numbers attached. The mites are typically 'picked up' during the later larval stages and they transfer to the adult on emergence. They feed on the damselfly's body fluid (haemolymph) and once mature will fall back in to the water.
David also saw a good number of Blue-tailed Damselflies and Common Blue Damselflies at Wall and Seggy Pools, along with a number of Ruddy Darters- captured beautifully below: