Thanks, Don.

May I ask what features show this to be a Baetidae?

Catfish,

Don may not have seen your question, so I hope he won't mind if I attempt to answer it. Baetid nymphs are "pisciform"--swimming types that typically have a long abdomen, short thorax, slender legs, and fringed tails. One way to distinguish most baetid nymphs from most other pisciform nymphs is by their long antennae. Some exceptions would be the nymphs of Isonychia (which have long antennae, but are fairly distinctive and unlikely to be confused for baetids) and a few of the "two-tailed" baetid nymphs that have shorter antennae. Your nymph had three subequal tails, but has lost most of the left cercus.

Due to the fine banding of the tails (not the broader band near the tips), Centroptilum or Procloeon are possibilities. However, I can't see the gills well enough to know if they are simple or compound. If they are compound, either Callibaetis or Cloeon (dipterum) would be likely. Compound gills appear to be double due to a recurved flap that is folded ventrally (Callibaetis) or dorsally (Cloeon).

I hope that helps.

Thank you, Lloyd, for your helpful comments. I have examined other photos I took of this individual, and it appears to me that the gills are compound and are folded ventrally.

Thanks again.

Best wishes,

Catfish