Hello senni, jackspeese,
this is interesting. Having "Googled" this a bit, the winter fly appears to be good bait for trout (amongst other fish) in the US.
Is "good bait" closer to the "spiritually weak" or "feeble minded" ?
I mention this as I thought "spiritually" was used in a ... humm... "religious" context.
Sorry, more questions than answers ...
Droops