Black ants will work all season. Ttrout and grayling start eating this fly when rain starts. Water from rain will flood the river bank and will flush these insects. Trout and grayling love these tasty ' snaks flies" because they are easy to be picked up from water film. The fly should be fished as dry or in subsurface of the water film. When rain is heavy this fly works fantastic as a wet fly too!We consider ants to be "a must" flies in everybody boxes!