I've had a few of these red hepts but never found the time to photograph one. They aren't common but they're probably worth recording. Wondered if the colouration's due to an imminent/recent growth expansion thang - any ideas?

One turned up this weekend from a tributary of the Afon Cych, it's compared with the standard inhabitants -












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Musha rig um du rum da

Nice!

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Save the softmouth trout

Beautifull Pics as always. We arent blessed with the clingers, But I look forward to finding out the explanation.

DB
I've always put a reddish colour down to the amount of red sandstone we have in the River Tawe.

OB

Is the colouration of red sandstone to do with Iron content?

WP
Yes, the red in old red sandstone comes from the presence of iron oxide.

The River Tawe is typical of many rivers in the south Wales coalfield; the rock formations are mainly limestone, red sandstone and millstone grit.

OB

Hellow little devil, I spoke to my nephew who has a PHD in things aquatic about these stone clingers and he was of the opinion that because they appeared amongst ordinary heptagenids these could be yet another import from the good old USA.
He tells me there is a variety of heptageniidae found in New Hampshire and Vermont called Maccaffertium Viccarium that is red.

This is quite correct, the 'American March Brown' can be reddish amber, once classified Stenonema vicarius, also a smaller Stenonema femoratum, they have been reclassified in new genus Maccaffertium. Obviously my ref books are detting dated.

Disturbingly exciting as it would be to have north American invasive Heptgadeniidae, my reference books show that diawl bach's example can't be of that Genus which exhibit truncated gills on segments 1 - 6 with slender thread-like gills on segment 7.
This would also rule out any reddish brown members of genus Rhithrogena which have larger gills on segments 1 and 7 than those on 2 - 6; the first and last forming a suction cup in some species.

I'm not saying the pictured example is genus Heptagenia, but the 7th gill is slightly smaller than 1 -6 which is a pointer. Probably red due to eating iron rich red algae as some have already pointed out.

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Save the softmouth trout

There is also Ecdyonurus to consider (image from Harris); anyway I think diawl bach has already determined the species, so I won't dig a bigger hole for myself.

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Save the softmouth trout

I'm also sure Diawl Bach will have already worked out the species. The smallest nymph in the first photograph is a member of the genus Rhithrogena and collected at this time of the year suggests it's a March Brown (Rhithrogena germanica).

The other two look like Large Brook Dun nymphs (Ecdyonurus torrentis), on the River Tawe there is a third colour variation that is very much darker (almost black). I've always put these colour alternatives down to the different types (colour) of stones found on the river bed; but it's only a guess on my part.

DB, I don't know the Afon Cych, is there any red sandstone present?

OB