Terrestrial fly patterns are designed to imitate insects that do not usually live on or in the water, but may accidently end up on the surface of the water such as grasshoppers and ants. Designed to float on the surface, these fly fishing patterns can be a lot of fun to fish at the right time of the year because they often produce a huge strike from a hungry fish. Terrestrial flies can also be used as a stimulator type fly.