Common Yellow Dun Heptagenia sulphurea

This stunning yellow mayfly seems to be quite local in Norfolk. I'm not aware of any other records in the mid Wensum area apart from the one below.

This was found in my garden moth trap one evening. One of its rear legs was missing and one of its front legs was malformed, with the femur about half the length and half the width of the opposite femur, the tibia being a bit short and wavy and there only being two tarasl segments before the claw. This femur was also darker and greyer than the normal one. Note: I initially mis-sexed this as a male on account of the rather large and protruding eyes, however on closer inspection it became clear that it was in fact a female. Some references suggest that the females are more brightly-coloured than the males, which fits.

female imago Common Yellow Dun Heptagenia sulphurea, North Elmham (Norfolk, UK), 3rd September 2025

The eye on this insect were clearly black, but the description in the book said it should be blue in both sub-imago and imago. There's an annotated inset photo showing that the eyes of newly-emerged sub-imago are black like on mine, but this wasn't a sub-imago (the wings are cloudier in sub-imagos). I'm not sure if the eyes become black again when it is freshly moulted from sub-imago or, and I suspect this may be more likely, this individual moulted to imago so soon after emerging that the eyes hadn't yet turned blue. Either way by the end of the night the eyes had turned blue as shown below.

same female imago Common Yellow Dun Heptagenia sulphurea on 4th September 2025, caught North Elmham (Norfolk, UK), 3rd September 2025