Tiny Baetis mayflies are perhaps the most commonly encountered and imitated by anglers on all American trout streams due to their great abundance, widespread distribution, and trout-friendly emergence habits.
Here's an unusually small early instar nymph.
This mayfly was collected from unknown in Wisconsin on March 1st, 2004 and added to Troutnut.com by Troutnut on January 25th, 2006.