a fly mask for horses has a cage structure supporting a mesh , the structure being formed of semi - rigid plastic splines which hold the mesh away from the eyes and most of the surfaces of the horse &# 39 ; s head . in a preferred form the fly mask has protruding lines at the location of the splines , protecting the mask against excessive wear due to rubbing of the mask against posts or other building structure when worn . a detachable protective nose guard can be included .