Large hatches of these last around one week from the first hatching duns to the last of the falling spinners. Large spinner falls can be found for two or three days. During this time it's not unusual to find a mixture of Ephemera simulans, and Ephemera guttulata on the water at the same time. Like guttulata spinner falls simulans spinners bring out large trout. The fly fisher will be amazed with the number of large freely feeding trout during this spinner fall. Ephemera simulans nymphs can be found in the muddy bottoms of large slow pools, and in the small gravel, and silt in medium riffles.