While I was searching for a detailed description of the Isonychia Bicolor (Slate Drake Mayfly), I came across this very informative site that can narrow down an unidentified aquatic insect that may be encountered while on the stream. If you have a mayfly, it asks how many tails it has, body length, geographical occurance, emergence water type, etc. If you happen to come across an unidentified bug on the river that the trout appear to be eating, take the bug home or try and remember how it acted/emerged. This could really help, especially if you are fishing for extremely selective fish. Beware, not all hatch charts list every single insect that is liable to hatch.