The Small Western Dark Hendrickson is one of those mayflies that don’t get a lot of attention until you encounter a hatch of them. They often hatch late in the summer when few other mayflies are hatching. They emerge from noon to mid-afternoon depending on the weather. The spinner fall in the evenings. They inhibit moderate to fast flowing water and are often found in streams with lots of vegetation. This is a mayfly that can hatch in fairly heavy concentrations and is one you certainly would want to be able to imitate if you encountered a hatch. This is the Serratella tibialis species.