These large insects are "trout candy" across the United States. Green drakes are the largest mayflies that provide fishable hatches in fast rivers. Look for hatches to begin in May & June on most rivers. Green Drakes are large insects and trout love them. When Green Drakes hatch in good numbers the trout forget all other foods and target drakes only. A dense hatch of Green Drakes can bring the largest trout to the surface.