Wednesday, October 19, 2011

Spiny Crawlers (Ephemerellidae): A Summary of the Year's Findings

Let's begin by reviewing a couple of things.  1) Peckarsky,, Freshwater Macroinvertebrates of Northeastern North America, pp. 26-29, key out 6 spiny crawler genera: Drunella, Ephemerella, Serratella, Dannella, Attenella, and Eurylophella.   Of these, I have found 4 in the streams I explore -- I have not seen Dannella and Attenella.   I'd like to find all 6 genera, so I intend to poke around in some new streams next spring.

2) The spiny crawlers in the 4 genera I've found all have gills on top of abdominal segments 4-7.  But the gill on 7 is always partially covered, and in the genus Eurylophella, the gills on 7 and 6 are both covered by the large operculate gills on segments 4 and 5.  (First photo below -- abdomen of Serratella: second photo below -- abdomen of Eurylophella.)

Now let me present my findings for 2011 in chronological order.

I. genus Ephemerella

1. E. subvaria

On January 19th, I found two E. subvaria nymphs in the Rapidan River in Madison County.   E. subvaria nymphs are brilliantly colored, and I've not seen them in any of the other streams that I sample.
They produce the "Hendrickson" hatch for fly fishermen, usually hatching sometime in mid-April (Knopp and Cormier, pp. 195-202).  I found more E. subvaria nymphs in the Rapidan on 2/23, and again -- but for the last time -- on 3/24.  Pictures from 1/9 and 3/24 are posted below.

Since by January the nymphs of this species are already fairly mature, they are obviously growing up in  the fall.  And lo and behold, I found a tiny E. subvaria nymph on a trip to the Rapidan River last month (9/12)!  He's got a long way to go.

2. E. dorothea

Most spiny crawlers we see in our streams are, in species,  Ephemerella dorothea.  During the three months of spring -- March, April, and May -- our streams are loaded with them.  They can dominate stream populations -- during their season -- like no other taxon, with the possible exception of black fly larvae during the winter.  The nymph in the photo at the top of the page was found on 5/18 in a small stream that flows into the Moormans in Sugar Hollow.  The three pictured below were found on 3/18 at the Whippoorwill Branch of the Mechums, 4/11 at the Rapidan River, and  4/23 in Buck Mt. Creek.

But the first E. dorothea I found this year, I found on 2/14 in Powells Creek in Crozet.  In February, nymphs of this species are still very small: the photo below is a microscope shot.

II. genus Eurylophella

This is a genus that is not well represented in the streams I explore.  I found one nymph in March (3/21) and another in May (5/30): that's it.  The first was immature; the second was fully developed, with long wing pads and well defined colors and patterns.  I would guess that the peak hatch for this genus in this part of Virginia is May to June.  I have tried to identify both of my nymphs to the level of species: I can't do it.  They might be E. verisimilis -- but I can't even tell if they are both the same species.  Clearly, I have more work to do over the winter -- microscope work and further research.  Here are the two nymphs that I found.  Note the large operculate gills on segments 4 and 5.

III. genus Drunella

I have photos of Drunella nymphs taken on 4/25, 5/9, 5/14, and 5/30.  I can only identify one to the level of species.  Remember that Drunella nymphs are distinguished by the tubercles (bumps) on the leading edge of the fore femora.

A. Drunella walkeri

I found this D. walkeri nymph in Buck Mt. Creek on 5/9.  It is unique in having "horn-like" projections on the front of its head -- the genae -- and by the long hair (setae) on the back of its femora.  In the photo those hairs are filled with sand and mud.

B. D. species (These nymphs appear to be either D. tuberculata or D. allegheniensis, and I'd favor the former.)

The two nymphs below were found on 4/25 and 5/30, both in Buck Mt. Creek.  Drunella is not a genus we commonly see, but if we see them it's in April and May.  Note the tubercles on the front of the fore femora.

In 2010, I saw a lot of Drunella nymphs in April in the Moormans at Free Union bridge (Rt. 601).  It's the only time I've seen a large number in the same place.

IV. genus Serratella

This is the spiny crawler -- the only spiny crawler, I think -- that we see in the summer.  I didn't see them in very big numbers this year, but they never show up in force like E. dorothea.  I found them this summer in Buck Mt. Creek, the Moormans River, and in the Rivanna.  All of the nymphs that I found were S. seratoides.  The photo below was taken on 7/19 at the Rivanna -- it's of an immature nymph.
The one I found at Buck Mt. Creek on 9/1was fully mature and ready to hatch.   I know that I saw them in the Rivanna last year in June.  So, you can look for nymphs of this genus in June through September.

Serratella nymphs are much darker than Ephemerella nymphs, but the distinguishing feature is the hair on the tails.  If you look at the nymph at the top of the page (Ephemerella) -- click on it to enlarge it -- you'll see that the tails (cerci) have segments set off by whorls of spines, and there are lots of fine hairs (intrasegmental setae) between each of those whorls.  There is little, if any,  "intrasegmental setae" on the cerci of Serratella.

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