Small Red Damselfly (Ceriagrion tenellum)
A very rare one for Somerset.
I believe I briefly saw one on Exmoor on the way up to Pinkworthy pond, but that is the only time I've seen one in Somerset. I will explore this area a little more to see if I can find more.
Males have a bronze/black thorax and a completely red abdomen.
Females have 3 forms; erythrogastrum (all red abdomen like the male - unusual), typica (red and black abdomen), melanogastrum (all black abdomen), all with a bronze/black thorax like the male.
Are only really going to be confused with Large Red Damselflies, but as Small Reds are so rare, if you see a red damselfly it is more than likely a Large Red.
The images below are all photographed in the New Forest.  I've only managed to photograph the female typica form to date.

Male
Male
Male
Male
Male
Male
Male
Male
Male (Stretching)
Male (Stretching)
Female (typica)
Female (typica)
Female (typica - Teneral / Newly Emerged)
Female (typica - Teneral / Newly Emerged)
Want to See 
Unfortunately, I know of no good spots in Somerset.
These like swampy land and streams or ponds nearby.
If you want to see them, a day trip to the New Forest would be the best place to go.
They like the seepages and small streams that run off them.

Especially Good
There are quite a few places to see them in the New Forest (Mid-June/July).
A place near Burley (what3words: spin.palaces.losing) is a good place to explore for them.
Park here and walk along the stream and up the seepages.

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