Stillborn mayflies, or cripples, are not that rare to imitate. I have fished a variant of CdC Z Lon Stillborn Crippe for years, but have now tied a version to fit the idea of using Z Lon in the body – such as in with the CdZ-Lon flymf and the CdC-Lon emerger variant.
I really can’t make up my mind if I like the standard emerger hook, or the semidropped like the TMC 200R. If you look at how most of the BWOs emerge, I guess the 200R has the most correct angle. But still, these curved grub-hooks seem to work very well for most mayflies.
Therefore, I always carry these patterns, but make sure also to have as many straight/slightly curved versions in my box.
Please look at the two flies linked above for a more detailed description of the techniques and material choices.
The standard hook that I use for these kind of flies are either the TMC 2488 or the TMC 2487, depending on the size of the emerger I am tying. But I also like the Hends grubs – usually in the BL versions.
This pattern can be adapted to any mayfly species, and if you don’t like the Z Lon approach, you might choose either standard dubbing, a biot or quill for the body. When tying the Ephemerella Aurivilli I usually choose golden olive and brown in the body.