Mice and voles are a food source for trout. The mouse fly is increasingly popular in the U.S. for catching big predatory trout, especially late in the evening or at night. The mouse fly is a firm favourite in New Zealand too, especially during mouse plague years. This happens every 5-8 years when all the beech trees flower at the same time and hence set seed at the same time causing the rodent population to explode and the trout to gorge themselves on the rodent bonanza.
While I haven’t caught on one in the UK, there are reports on some of the fly fishing forums of fisherman finding voles in the stomach contents of trout they have caught, Nant-y-moch being one that I recall reading about. Perhaps worth having one in the fly box for evening or jack pike fishing.
Tight Lines
Greg