(Price for 12 Flies) Mouse / Rat Natural Color The deerhair Mouse fly pattern is compact enough to imitate local voles, water rats, shrews, lemming, mice and baby rats. These little mammals can often be found swimming in the water. You will want to research and scout the water you are going to fish. Spend some time there during the day as to get a general layout of the river or lake so you can avoid any pitfalls. Also look for areas were a big trout might hunt during low light hours. Shallow, swampy water that is often overlooked during the day can become prime hunting grounds at night. Often times big trout will move into these areas looking food once the sun has gone down. Back eddies, large bends, dead fall and so on that create soft water should all be places you consider for night time mousing arenas.