The Perfect Fly Female Trico Spinner is a imitation of the spinner stage of life of the mayfly. There is a female and male imitation because they are different colors. Once the dun reaches the banks, trees or bushes, it molts into a spinner, or the sexually mature adult. The males and females return to the water and mate in mid air, and eventually fall dead on the surface of the water where trout can easily dine on them. It should be fished on the surface and treated with floatant.