Thursday, April 14, 2011
The Treasure Hunt -- Finding Another Gem
A friend of mine compared my looking for insects to a "treasure hunt" -- pretty well said. I never know what I will find, but whatever it is, it's bound to result in some beautiful pictures, and every so often I get a surprise -- something totally new! This time -- not a new "genus" of Perlodid stonefly, but a new "species". This is a Perlodid stonefly, genus Isoperla, species similis. I've never seen one before, and I never would have guessed this was a new Isoperla. Every Isoperla Perlodid that I've seen before in our streams had brown stripes running the length of the abdomen -- which is a defining feature for most species of Isoperla -- but not all. When I got home and keyed this out to Isoperla, I went to some internet sites for confirmation. Sure enough -- Isoperla similis (two sites you might want to look at: 1) http://bugguide.net/node/view/20605/bgimage?from=24, and 2) http://www.pbase.com/tmurray74/image/110648194). I did find a "normal" Isoperla (I think it's Isoperla frisoni or Isoperla bilineata) at the same site this morning (the site goes unnamed); it's to the right and behind in the photo below, a side-by-side comparison. (The tolerance value for Isoperla similis, by the way, is ".7"; for Isoperla bilineata -- which is common in our streams -- "5.5".)
At the same site, I found a number of Green stoneflies (Chloroperlids), a common netspinner (genus Diplectrona), a few Uenoid case-maker caddis, some prong-gilled mayflies, flatheaded mayflies (genus Epeorus and Leucrocuta), a rolled-winged stonefly (Leuctridae), and one lonely Ameletid mayfly. Finally, I found a "pupating" caddis. When I put its little rock "dome" on its back, the cocoon was easily seen.
I suspect this was a common netspinner pupa: to be sure, I'd have had to take it back home, open up the cocoon, and look at the developing pupa under the scope. I decided to return it to the stream.
On my way back to town from this adventure, I decided to have a look in the Whippoorwill Branch of the Mechum. It is absolutely "lousy" with spiny crawler mayflies. This is common for this time of year, and I'm sure the StreamWatch volunteers are running into large numbers of them in the streams that they sample. In the photo below, I got a good picture of a spiny crawler "crawling" over a stonefly (common stonefly, genus Eccoptura).
If you want to go out looking for "spinys" and not work very hard, turn over rocks that are covered with moss (well, I don't know my grasses, so I doubt that it's "moss," but it's moss to me). Lift the rock out of the water and wait a few seconds. They'll start moving out of every blade of grass you can see!
I lifted some rocks today that easily had 40-50 nymphs moving around in that vegetation.
One final look at our "catch of the day": Perlodid stonefly, Isoperla similis.