March Brown mayflies, aka Rhithrogena morrisoni, are currently (or soon will) be emerging from rivers all across the American west. They are leaving behind the year-long aquatic nymphal stage, newly sporting the mottled wings of the dun, or subimago phase, as shown in the attached images. The duns rest in the streamside forest or vegetation for two or three days. But metamorphosis is not done with them yet. Mayflies are the only type of insect that sports two adult winged stages. After the brief dun stage, they molt and transform once again into the final sexually mature spinner, or imago, stage. The wings are then no longer mottled, but clear like cellophane. After swarming above the water in a mating dance, the females lay their eggs and die. Their entire air-breathing existence lasts less than a week.
The male dun pictured below was about 12 mm long.
So now, a question. What are your thoughts on the attached color, vs. the monochrome versions below?
