The Stream Doctor

March 3rd, 2003

Your questions and answers about everything stream related.

Q. I have a friend that has got me thinking about mayflies...and I am stumped. He says that he witnessed a hatch of some small insects that appeared to be almost like a blue wing olive one day. Quite a few got trapped in his vehicle since he left his windows open. We he got up the next morning, and as the temperature started rising, he noticed that the small flies were hatching or shedding again! Only this time, the flies were much more pale in color and slightly smaller. Anyway, I just wanted to know if this is a normal occurrence with some mayfly species, or if we are just imagining it!

A. No, you didn't imagine anything. What you witnessed was quite common in mayflies. These insects initially hatch from the nymph into a sub-adult, or imago, form which is duller in color and less active and which anglers refer to as the "dun." After a short period of time, they undergo a second molt into the true adult - usually, as you observed, lighter in color, shiny, and active. It is in this form that they take flight and mate.

~ C. E. (Bert) Cushing, aka Streamdoctor
105 W. Cherokee Dr.
Estes Park, CO 80517
Phone: 970-577-1584

The 'Stream Doctor' is a retired professional stream ecologist and author, now living in the West and spending way too much time fly-fishing. You are invited to submit questions relating to anything stream related directly to him for use in this Q & A Feature at

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