This reasonably rare dragonfly gets its very apt name from the obvious swollen tip on its abdomen. This is present in both he sexes with subtle differences in the anal appendages.
It is confined to the southern half of the United Kingdom in a few specific sites. This species prefers slow flowing rivers where they breed, although adults can be encountered far from water. One of their strongholds is on the River Thames.
I regard this species as rare in my part of the UK as there are only relatively small satillite populations on the River Kennet, which has been my only hunting ground for this dragonfly. I have heard of them being on the River Blackwater but this is unconfirmed.
Perching adults are a rare site. The adult male is dull green and black and I have yet to see one, but I am still searching. The adult female is yellow and black and closely resembles an immature specimen.
It is these immature Club Tails that you are much more likely to encounter on days of an emergence. On such days they can be quite abundant and you must make the most of the opportunity, it may not arise again.