Thoughts on the Spiny Crawler "Explosion" and Evaluating our Streams

As I've noted in entry after entry for the last month or so, our streams -- all of them -- are loaded at the moment with spiny crawler nymphs.  When I go through the leaf packs or pick up a rock that's covered with moss, there is so much movement and activity that it's almost like looking into a beehive.  Spring samples done by groups that monitor streams are often overwhelmed by spiny crawlers -- I speak from personal experience.  But this can have a negative impact on the score of a stream for two different reasons.

Reason1.  One of the factors that is important in "scoring" a stream is the tolerance values of the insects we find.  At the moment in the state of Virginia, the DEQ sets a value on ALL spiny crawlers, regardless of genus or species, of 4.0.  That's rather high for a mayfly.

Now, how many spiny crawlers, and which spiny crawlers in terms of genus and species, have we seen so far this year in our streams?   We've seen 6 different spinys, and we'll see a 7th come the summer.  They are --

1. Ephemerella subvaria.

2. Ephemerella invaria:

3. Ephemerella dorothea:

4. Drunella walkeri:

5. Drunella tuberculata.

6. Eurylophella

and 7. Serratella serratoides (the spiny we see in the summer)

North Carolina, unlike Virginia, assigns tolerance values by genus and species.  The tolerance values they use for these species are as follows:

1. Ephemerella subvaria:     undetermined (species too uncommon)
2. Ephemerella invaria:       2.6
3. Ephemerella dorothea:    3.3
4. Drunella walkeri:            0.6
5. Drunella tuberculata:      0.0
6. Eurylophella spp.:           4.0
7. Serratella serratoides:     1.7

If we use -- as we do in Virginia -- a TV of 4.0 across the board for all spiny crawlers, are we getting an accurate reading on the health of our streams?  Now, a caveat here: I would bet that 90-99% of the spiny crawlers we find in March -- May in this part of Virginia are E. invaria (2.6) or E. dorothea (3.3): those are the species that really "explode".   Still, with the large number of spiny crawlers we find in the spring, the NC tolerance values will result in a quite different score than the one we'll find using the 4.0 of Virginia.

Reason 2.  Biological diversity is another factor that's taken into account in evaluating the health of a stream, and many groups that monitor streams aim for a sample of around 200 insects.  At this time of year, depending on where you put your net into the stream, you could easily end up with, say, 150 spiny crawlers -- or more -- in your sample of 200.  If you're hoping to have 15-25 "families" represented in a balanced way -- the sign of a "healthy" stream -- you'll be mightily disappointed.  But, this is their season.  I go to some streams that would have to be considerd "pristine," but at the moment any samples done in those streams would be dominated by spiny crawlers.  Is it right to "downgrade" a stream based on what is simply a fact of life?  And trust me, if you go back to those streams in June, you'll be hard pressed to find any spiny crawlers at all.

Random thoughts and concerns of an amateur entomologist, and I'm sure that people who assess the health of our streams must take these things into account.  If not, I sure think they should.

Not Quite Ready to Fly: Maturing Insects in a Small Stream in Sugar Hollow

As we saw yesterday, the prolific spring hatches have already begun.  But today I just saw the insects that are still getting ready to go.  Above -- a beautiful, big, Common stonefly (family: Perlidae): Acroneuria abnormis.  Notice how the wing pads have started to darken and how pronounced the abdominal banding has become (on A. abnormis nymphs, the abdominal bands are dark at the front and light at the back.)  This nymph was about 1 1/4" long, and it will hatch as a "Golden Stone" in June or July.

And while I was expecting to see more adult green stoneflies (Chloroperlids), since they were all over the rocks yesterday, today I only ran into maturing nymphs.  But it's an insect that is really quite handsome.

In the photos I took yesterday of the adults, the three black dots on the head -- the ocelli -- were very prominent -- the head is lacking in any other design.

When we take a close look at the head of the nymph we see that this a feature that just carries over with the emergence.

Probably not a bad time to remember what these, now beautiful, stoneflies looked like back in November:

Why, they're just like us: the older they get the better looking they are (!)

Two more insects that are clearly maturing and getting ready to hatch: the freeliving caddisfly larva Rhyacophila fuscula, and the Northern case-maker, genus Pycnopsyche.  The former was also about 1 1/4" long and will surely enter pupation any day now: the latter has fashioned a case of pebbles, firmly cemeted together with silk, which it will soon seal off for pupation.

And then, we have the spiny crawlers.   At the moment, there are so many of them in the leaf packs and on the rocks that it's hard to find anything else.  I've got to think that the spiny crawler hatch, which normally happens in May, is the most prolific hatch that we see in central Virginia!  The nymphs I was seeing today were, as they were yesterday, the species E. dorothea.   They seem to have replaced the E. invaria nymphs that we saw earlier in the season, a fact that Steven Beaty seems to confirm: "Ephemerella invaria appears to emerge earlier than E. dorothea, with peak abundance in March." ("The Ephemeroptera of North Carolina," p. 27).   Anyway, a token picture.

The only "youngster" I found -- other than a number of "teenage" Giant stoneflies -- was the Perlodid stonefly, Isoperla holochlora.

 I. holochlora is, I think, the last Perlodid stonefly of the season to show up in our streams, and according to Beaty ("The Plecoptera of North Carolina,"), we can see these in our streams right into August.  The mature nymph in the photo below was found on June 13th, 2011 in the same stream I went to today.

(Below: a mature common stonefly and an immature Isoperla holochlora Perlodid stonefly.  Quite a difference in size!)

Spiny Crawlers (E. dorothea), Flatheaded Mayflies (Rhithrogena) and Much More at the Upper Doyles River

The rocks in mid-stream were covered with these little yellow stoneflies today.  Below is a photo taken on Sunday (4/15) of what appears to be the very same species that was sent to me by a friend (used with permission).

While neither one of us is an expert on stonefly adults -- we mainly work on identifying the nymphs -- based on similar photos by Tom Murray and others, our guess is that these are Chloroperlids (Green stoneflies), Sweltsa onkos (see, for example, http://www.pbase.com/tmurray74/image/125030450).  It was pleasant to be working with them as companions, while watching mayflies hatching as well.

The Upper Doyles is filled with insects at the moment -- well, that's true for a lot of our streams: lots of Rhithrogena flatheaded mayflies and spiny crawlers, all E. dorothea.  Let's take a look.

1.  The flatheaded mayfly, genus Rhithrogena.

A real beauty with the black wings of a nymph that's fully mature.  We'll let this nymph represent the possibly "hundreds" of these that I saw today.  I picked up one rock, not a very big rock, and counted 35 Rhithogena nymphs gathered together, side-by-side, in a space that was 2" X 3" -- and they just sat there looking at me!  I see this genus of flathead in very few streams, but it seems when I find them, I find them in very large numbers.  I reported the very same thing from the Lynch River on 3/29.  At the Lynch River these were joined by a lot of Diploperla Perlodid stoneflies, and I found the same thing today.

Diploperlas seem to have a "sweet tooth" for Rhithrogenas: the two Diploperlas in the photo above did in two of my Rhithrogenas before I quickly moved them into a bowl of their own!

2. Spiny crawlers: Ephemerella dorothea.

(Normal eyes on the first; large, red eyes on the second.  Is this a female/male difference as we found with the small minnow mayflies?)

I took a number of photos today with a new lens -- a "super" macro lens that magnifies from 1X -- 5X.
Here's a closer look at one of the spinys.

I also drew down on the abdominal segments to see if they had tubercles on them, taking this photo.

 It shows that they did not.  Lack of paired tubercles on the tergites -- tiny projections that stick out from the back of the tergite -- is one of the things that helps us ID these nymphs as E. dorothea.

I took one other photo with my new "super" lens for you to see.  I flopped my Rhithrogena nymph on its back and tried to get a good ventral view of the gills.  You'll recall that this is the flathead on which the gills form a complete oval.  I think you can see how the gills at the rear of the abdomen overlap.

When I get proficient at using this lens, I hope to use it more in my work.  It will allow me to photograph key anatomical features without using microscope photos of preserved insects.

One other thing from today.  I saw a lot of Isoperla holochlora Perlodid stoneflies that are more mature than the ones I've found so far this year: note how the rear edges of the wing pads are starting to bow.

Going, Going -- Well, Not Quite Gone: "Yellow Sallies" (Isoperla namata)

I took this photo of a "Yellow Sally" last year on May 14.

"Yellow Sallies" are the adult, terrestrial form of the Perlodid stonefly Isoperla namata.  At the moment, they're hatching throughout central Virginia.  The hatch will continue into May, but I'm now seeing very few nymphs in the streams that I visit (I only saw one yesterday at Buck Mt. Creek).

I've been taking photographs of these nymphs -- this species -- every month, beginning in November last year.  So, I have a good set we can use to trace the changes this insect goes through as it develops.  Let's look at the following photo -- which I took one week ago on April 11 -- as a reference point to use as we go along.

The nymph in this photo is fairly mature -- the wing pads are starting to darken.  Remember that I. namata Perlodid stoneflies have a dark transverse band on the head, from which two black lines drop down to the rear ocelli (lines in front of eyes).   Often, there are two dark spots/lines at the rear of the head, though on some nymphs these rear spots/lines are missing.  There are three stripes on the abdomen (this is true of all Isoperlas), two on the sides (lateral) and one in the middle -- the middle "line" is made by a sequence of "crosses" on each of the abdominal segments.  Finally, when the nymph is mature, the rear wing pads angle away from the body more sharply than the front wing pads (note the angle of the arrows) -- but this is true of all Perlodid stoneflies.

Sample 1: November 8, 2011

Since the head pattern has not yet developed, I can't be positive of my identification.  But, it was an Isoperla, and since I. namata is the first Isoperla we see at the start of any new season, I think I. namata is a reasonable guess.  Features: 1) it is possible to make out the lateral stripes on the abdomen (click on the photo to enlarge it): 2) note that the rear edges of the wing pads at this point seem to be straight across, if not convex in shape.

Sample 2: November 18, 2011

We can see all three abdominal stripes.  And on the head, the light spot at the front of the head is starting to show, and we can start to make out the "dark spots/lines" at the rear of the head.  Note that the rear edges of the wing pads are starting to bow inward, more true of the rear wing pads than the front wing pads.

Sample 3: December 13, 2011

While the abdominal stripes are not very clear on this nymph, the head pattern is starting to round into form.  We can see the transverse band, and we can see the black lines dropping down from it touching the rear ocelli, though they're still on the "thick" side at the moment.

Sample 4: December 26, 2011

The head pattern looks much the same as on the previous nymph.  But note how you can distinctly make out the "crosses" forming the middle abdominal stripe.

Sample 5: January 4, 2012 

No doubt about this nymph being Isoperla namata.  The three abdominal stripes are prominent now, and the head pattern is well defined.  However, note how the two "lines" that drop down from the transverse band on the head are still rather "thick" -- i.e. they've not really thinned into lines.  Wing pads are still straight across on the back edges, though bowing in slightly.

Sample 6: December 21, 2011

One significant change: those lines that connect with the ocelli are thinning out as the pale space between them widens.  Rear edges of the wing pads remain much the same.

Sample 7: February 2, 2012

The abdominal stripes are fully formed, and the head pattern is fully developed -- but, note that this is one of the I. namatas that does not have the dark spots/lines at the rear of the head.  Big changes: 1) color -- the nymph is now a pale yellow/orange, shades that will soon be enriched; and 2) rear edges of the wing pads -- note how they are bowing/arcing in towards the middle.

Sample 8: February 23, 2012

Note the wing pads: they are much longer, and the rear wing pads have started to flare away from the body.  The front and rear wing pads now move away from the body at different angles.

Sample 9: March 9, 2012

Richer colors.  The lateral abdominal stripes are a little bit thicker, while the "crosses" in the middle stripe stand out in a prominent way.  The wing pads are longer and more fully patterned than those in the previous picture.

Sample 10: March 28, 2012

This is a nymph that is fairly mature: the wing pads have started to darken.

Sample 11: April 11, 2011 (I had to go back to last year's collection for this one.)

Fully mature and ready to turn into the adult terrestrial that we see at the top of the page!