Tuesday, October 29, 2013
Large winters/Small winters: how to recognize them when they're small
They're are a lot of people sampling streams at the moment as the fall sampling season comes to its close. If you're out there, and you live in our part of the country, there's a good chance you'll be seeing tiny, large winter stoneflies (genus, Taeniopteryx) and small winter stoneflies (genus Allocapnia). Your monitors will probably urge you to keep them for identification back at the lab.
But, it's actually fairly easy to ID them right in the field for those of you urged to do family level ID.
That's a large winter stonefly in the photo at the top of the page. The photo was taken on 10/27 last year. Clearly, it looks nothing like the large winter stonefly pictured in Voshell's Freshwater Invertebrates, p. 134. He's showing you what they will look like when they're mature. More like this.
But you can probably ID these large winters right in the field with a loupe, even at this time of year.
Look for 4 things. 1) These nymphs are "freckled," "spotted," the colors range from gray (very small) to reddish brown (somewhat larger); 2) The bases of the antennae are unusually thick; 3) There's a pale , medial stripe running from the head to the tails; And 4) to really be sure that this is a Taeniopteryx large winter stonefly, flip it over and look for "coxal gills."
They look like bean sprouts, and they're very large on the very smallest of nymphs.
Small winter stoneflies. They always show up towards the end of October.
And there are two ways to recognize them. 1) When they're small, they're virtually transparent. When I put them into my petri dish to take a picture, I sometimes have trouble making out where they are. And 2) they're "floaters." Maybe they're just too light to sink! They always seem stay on top of the water when put into a tray.
This feature is commonly seen even with larger nymphs -- even when they're mature.