Thursday, February 17, 2011
Spiny Crawlers: Two More Genera
The photo above was sent in by one of our readers -- who chooses to remain anonymous. This is a spiny crawler mayfly nymph, found in the Moormans River in April, 2005 -- genus Eurylophella.
I did not discuss this genus in my entry of 1/30/11(The "Super Hatches" of Spring: "Spiny Crawlers" and "Nemourids") because I had never seen one, and I did not know they could be found in our streams. I am grateful for this photo, and you can be sure I'll be lifting up rocks in the Moormans this spring!
The spiny crawler genera reviewed in my earlier entry were Ephemerella, Serratella, and Drunella: the most common genus we see is Ephemerella -- and that's in the spring. Ephemerella nymphs -- and this is true for Serratella and Drunella genera as well -- have gills on top of abdominal segments 3-7, though the gill on segment 7 is totally or partially hidden by the gill on segment 6. Here's a photo (Ephemerella) to remind us of the arrangement.
Note that this isn't the case for genus Eurylophella. Eurylophella nymphs have gills on segments 4-7,
but the gill on segment 4 is large and operculate and covers the rest of the gills, save for the bottom edge of the final gill. Let's have another look at the donated photo.
As with the operculate gills on "small square-gill" mayflies and "little stout crawlers," these large, operculate gills on Eurylophella protect the fragile gills underneath and prevent them from silting up. Thus, this is a spiny crawler that has adapted to living in slow moving water.
There is another Ephemerellidae (spiny crawler) genera with a similar arrangement of gills that I found on a recent fly fishing trip to Montana -- this genus, to my knowledge, does not exist in the East. The genus is Timpanoga, and the preserved nymph below is Timpanoga hecuba. Fly fishing guides look to this for the "hecuba" hatch in September.
It's downright scary! And it's large. This specimen is about 3/4" long, not counting the tails. But, look at the arrangement of gills.
Again, there is the single, large, operculate gill on segment 4 that covers everything else save for the bottom of gill number 7.
To match it's short, stubby tails, by the way, it has a weirdly squared off head!
This nymph was on a silted rock in the shallow water at the edge of the Bitterroot River.