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3. A Couple of Stone Adults

Ran into a couple adult stones on a local river today and was hoping someone might be able to help me figure out what genus and/or species they are. I have a key for my area's mayflies, but nothing on stones or caddis yet-- would love to hear any book recommendations with these in them.

Both were found on a small northern Michigan tailwater (just north of 45-degrees lattitude). I still have both of these and can take additional photos if a closer look at anything is needed for a positive ID. I also have a microscope and can report anything at the micro level, if needed.

The early black stone is exactly 10mm long from the front of the head to the rear tip of the wing. The early brown stone is 14mm for the same distance.

Thanks for any help!

Hi Alex,

Both are in the family Taeniopterygidae and are commonly known as Early Black or Brown Winter Stoneflies or Willowflies. The brown one looks like Strophopteryx fasciata (Mottled Willowfly) and I'm thinking the smaller dark one is a male of the same species.

Thanks! I really appreciate the help. I didn't realize that you get that much color variation between sexes of the same species with stones, but now that I think about it, its kind of silly that there wouldn't be.

Are the horn-looking things folded up onto the tip of the abdomen on the male what it uses to grab onto the female?

My pleasure, Alex. As to your question, the answer is yes and no. I believe your premise is correct that Stoneflies do grab on after a fashion, but they copulate terrestrially as opposed to aerially (as mayflies do) so their genitalia are structured to meet different requirements. What appears to be claspers in the photo are actually lateral parts of the underlying segment up against the process. If you take a lateral photo (with the wings and leg out of the way) it should show the process jutting distinct from the sterna posteriorly and turning up slightly at its apex.

Thanks for the info! You learn something new everyday. How did you determine these are fasciata? Not that I question it, I'm just curious what you're supposed to look for with these guys. With Mayflies, I "see" the differences between species, but with stoneflies-- and many caddisflies-- they all look the same to me, other than color and size.

Well, the family is easily determined in your crisp photos as they clearly show the unique tarsal segment ratios. Going beyond the overall look of the critter that points to the Mottled Stone group of species are diagnostic characters a bit more esoteric. The wing venation/spotting pattern, and more importantly the shape of the 9th sternal processes look to be right.