Ethan Bright conceived and developed keys to the Odonata nymphs of Michigan. His expanded project, the Aquatic Insects of Michigan, now has it’s own website.
The section with the keys to Odonata can be accessed directly here.
This is an ongoing project, and Ethan can be contacted at ethanbr AT umich.edu.
~
The Atlas of Common Freshwater Macroinvertebrates of Eastern North America provides a basic guide to characteristics of the nymphs of Odonata families.
For those willing to take a deep dive into identifying dragonfly nymphs, using many recent advancements, we recommend this book:
Tennessen KJ. 2019. Dragonfly Nymphs of North America: An Identification Guide. Springer, Berlin/Heidelberg.