First, come the Red-eyed damselflies (Erythromma najas), a dragonfly species I first saw in May 2024 so, each year since, I have looked forward to finding them again. Though they can be seen as early as April and linger in to September, the core months for sightings are May through August, and I usually see them locally from mid May. The British Dragonfly Society website says this species is ‘[m]ost common in central and southern England, and the Welsh Borders’, but ‘[a]bsent in Scotland. It has increased in occupancy in England since 1982 and in Wales since 2006.’ Perhaps, as the planet warms, folks living further north will also get to see those startling red eyes staring at them from a waterside bush.
Then come the Small red-eyed damselflies (Erythromma viridulum), six to eight weeks after the Red-eyeds – their core months for sightings are July to August. And, as both species are often seen in the same locations and both could be active at that same time, that’s when things become a little more tricky as they are very similar and their size difference is not an easy distinguishing feature to use. I’ve placed photographs of males of the two species below, the top image shows Red-eyed, the lower Small red-eyed, to try to show the differences.
There are a couple of features I look for to help me work out which is which. The upper black line on the side of the thorax often ends in a dot in Small red-eyeds but this is rarely the case in Red-eyeds. Also, the blue segments on their tails are different – in the Small red-eyeds, the sides of segments 2 and 3, and segment 8, are blue; I find this the easiest feature to spot in the field (or, perhaps, I should say by the water). I should warn that these differences only apply to the males of both species; the females are not so straight forward, and it’s probably best to check the British dragonfly Society website, where they show excellent side-by-side comparison photos that are very useful.
Small red-eyed damselflies only appeared in Britain in 1999 but have since spread at a quite remarkable rate (the pair shown above are doing their bit to help with that spread). The latest map on iRecord shows records, though still sparse, down to the tip of Cornwall, across the southern part of Wales, up to the Lake District in the west of England and, in the east, a scattering of records in southern Scotland.
If they’re males, a good view of the dark stripes on their upper wings can clinch an ID; if they’re females, a front-on view of the undersides of the tips of their antennae is required (see my blog 
