Megaloptera: Hellgrammites and Alderflies

When I started this blog, I decided I would not post an entry on Hellgrammites -- since everyone knows what they look like.  But, with almost 6 inches of rain last week, our streams have been slow to recede, and here I sit with time on my hands.   So.....

Hellgrammites (family: Corydalidae) and Alderflies (family: Sialidae) are the only two members of the order Megaloptera.   I think there's a very good chance that if you tell someone you're lifting rocks in a stream looking for aquatic insects, they'll assume you're finding Hellgrammites -- or possibly Crayfish (which, of course, are not really insects).  Hellgrammites are insects; they have three pairs of legs, and what we see in the stream are the larvae -- which hatch in the summer into quite interesting looking terrestrial adults (for some good photos of the adults, go to: http://bugguide.net/node/view/3609/bgimage (multiple pages of photos).   After mating, the female afixes her eggs to the bottoms of bridges or trees overhanging a stream: when they hatch, the young larvae simply drop into the water.

If you've ever picked one up, you know they have nasty "pincers" (jaws), and they will happily bite into   your finger!  I'd urge caution in handling.  And, they can grow to a pretty good size: 2" or more for a mature larva is not at all uncommon.  There is probably no need for a detailed description since almost all of us recognize them when they are large.  Two photos will help to focus on the key features.

As we can see from this photo, they have "paired lateral filaments" on abdominal segments 1-8 and 10, and

there is a pair of hooks on each of the prolegs at the end of the abdomen (this photo shows only one of the prolegs clearly).  This detail is probably not necessary for identifying adults -- but for "baby" hellgys (a little "Bob" slang), the four hooks on the prolegs tell the tale (though we're normally looking at them through a microscope).  We see "baby" hellgrammites in samples from July through September, and they can be confused -- when they're on your net -- with common netspinners.  Here is a microscope photo of one:

But note the hooks:

Hellgrammites are common in our watershed: they are found in almost every stream sampled by StreamWatch.  Normally, the numbers are small (i.e. 1-8 per sample), but large numbers have shown up in samples in Cary's Creek, Long Island Creek, Mechunk Creek (55, 58), and the Lynch River.  StreamWatch (and VA DEQ) give Corydalidae (hellgrammites) a tolerance value of "5"; in some parts of the country they're given a value of "0" -- but a lot of this varies with genus.

The other member of the Megaloptera order -- Sialidae ("alderfly") -- has been found in our streams only rarely.  In the StreamWatch data that I have reviewed, I see "1" listed in a sample for Cunningham Creek, "1" listed in a sample from Raccoon Creek, and we found 1 last year (year before last?) in a sample I helped with at the Mechunk.  (Naturally, it took Rose to figure out what it was!)  Sialidae has a tolerance value of "4".  Picture:

I don't have a good picture.  This is a microscope shot of the one we found at Mechunk Creek.  Alderflies also have "pincers," and they can be mistaken for small hellgrammites -- but they don't look quite right.  The big difference is that they don't have prolegs with hooks.  Instead, abdominal segment ten "has a single long, tapering filament, fringed with fine hairs, that projects to the rear"  (Voshell, Freshwater Invertebrates, p. 148).

How Discoveries are Made in the Lab: The Nemourid genus Nemoura

I've commented in several previous entries on my delight in finding this stonefly -- Nemourid, genus Nemoura -- in a number of streams in the last 3-4 weeks.   In the first year or so that I worked with StreamWatch, we occasionally found several of these in winter samples; we were not really sure what they were.  Our feeling was that this was a large winter stonefly, genus unknown.  We were familiar with two genera of large winter stones -- Taeniopteryx and Strophopteryx.   But these could not be Taeniopteryx nymphs since they lacked "coxal gills" (see the entry for 12/16/10), and they could not be Strophopteryx nymphs since they lacked a "triangular apical plate" (see the entry for 12/17/10).   There are other genera of large winter stoneflies, and we (myself and Rose Brown) carefully worked through our dichotomous key (Peckarsky, et.al., Freshwater Macroinvertebrates) to figure this out, but we could not pin it down.  That this stonefly was a Nemourid stonefly, we just figured out about six months ago.

Why did we think this was some genus of large winter stonefly?  Three reasons.  1) We saw these in winter samples -- often those done in February -- and that's when large winters abound.  2) The wingpads on this nymph were almost exactly the same as those we find on large winters.  Some pictures.  First, these are the wingpads of a large winter stonefly (genus Taeniopteryx):

And these are the wingpads of our unknown nymph:

Very difficult to distinguish.  And 3) while we knew that the wingpads of large winter stones and Nemourid stones are almost exactly alike -- this could not be a Nemourid!  We see Nemourids a lot in the spring, and they all look like this:

I.e. they always have "cervical gills," those frilly gills sticking out on both sides of the neck.

It was not until we took a closer look at Peckarsky -- and took a closer look at the legs of our nymph -- that we discovered what we had missed.  And that was two things.  1) As I've noted before, tarsal segments 1 and 2 on large winter stoneflies are the same size: on Nemourid stoneflies they are not, tarsal segment 2 is smaller than 1.  Our unknown nymph had Nemourid tarsi!

Tarsal segments 1 and 2 -- large winter stonefly:

Tarsal segments 1 and 2 -- Nemourid stonefly:

2) The other thing we discovered by carfully re-reading our key was that not all Nemourids had cervical gills!  In fact, cervical gills are only found on the genus Amphinemura.

All that remained to do was to identify the genus of this "new" (for us, anyway) Nemourid.  A close look at the pronotum showed that this was genus Nemoura.  The Nemoura pronotum has "...a distinct, single lateral fringe of spines of equal length..." (Peckarsky, p. 67), and the "pronotum is rounded laterally[with] longer, thinner setae absent from the lateral fringe." (Peckarsky, p. 67)  In the photo below, the yellow arrows point out the fringe of spines.

As I think I've mentioned before, the Amphinemura Nemourids (with the frilly gills) are common in StreamWatch spring samples -- and they can be found in very large numbers, sometimes forming the dominant taxon.  A review of the StreamWatch data shows that 1) most are found in April (some in March, some in May), and they are widespread in the watershed, being found in: both reference streams (in Albemarle County and Fluvanna County), Ballinger Creek, Buck Island Creek, Buck Mt. Creek (both sites), Cary's Creek, Cunningham Creek (both sites), the upper Doyles River, Lickinghole Creek, Long Island Creek, the Lynch River, Mechunk Creek (both sites), and the Roach/Buffalo River.

Clearly, the genera Nemoura and Amphinemura are not in our streams at the same time.  I've found the Nemoura Nemourid in February and March -- and they're already mature, preparing to hatch: I've not yet seen even a tiny Amphinemura (though I suspect they're around).  Amphinemura Nemourids mature in April and May.  I also wonder if they are found in the same streams -- or if they prefer different habitats.  I have found the genus Nemoura in Buck Mt. Creek -- where we also find the genus Amphinemura.  My other sightings have been in Elk Run (a Buck Mt. Creek trib), the Moormans River, an unnamed tributary to the Moormans, and the Rapidan River near Wolftown.    More to be learned, always more to be learned.

Notes on the Photography of Aquatic Insects

I thought I'd make some comments on how I go about taking my pictures.  But let me say at the outset that I'm not only an amateur entomologist, I'm also an amateur photographer.  There could well be "good" photographers out there reading this blog: your suggestions and criticisms are certainly welcomed.

1. First of all, a note on viewing the photos.  Now, you probably already know this -- but I didn't until I was fooling around last week.   If you click on a photo while reading the blog, it enlarges the photo: the quality is much improved.  When you're done, simply close the enlargement and you'll go back to the blog.

2. A reminder that I have a Flickr account where I post a lot of my photos: http://www.flickr.com/photos/aquaticinsects_of_central_virginia.  I've just recently added two new "sets" or "folders": Personal Favorites, and Live Photos Only.  I'm very partial to the "live photos," and hope to end up with live photos of every family and genus (of Mayflies, Stoneflies, and Caddisflies) that I can find in our streams.  If you haven't preserved any larvae or nymphs, you would not be aware of the change that occurs when the alcohol does them in: the vibrant colors are almost always lost -- they're either entirely "bleached" out, or in the least, they're dulled by transformation.   One quick example:

Fingernet caddis, live photo:

Fingernet caddis, preserved:

I preserved this spiny crawler that I found in the Rapidan River, and in the preserved sample, all of the bright colors were gone; it appeared to be dull and dark -- and that's a shame.

One more example.  Note what happens to an Ameletid minnow mayfly when it's preserved.
Live photo:

After preservation:

So whenever possible you certainly want to go with live photos.  How do we do it?

3. My equipment:  My camera -- despite what it cost me -- is seen as a "starter" in the SLR class.  I have a Canon EOS Rebel Xsi.  But more important than the camera itself is the lens.  A good macro lens is a must for good close-ups of these very small insects.  I have a Canon EFS 60mm f/2.8 Macro USM, and I'm very happy with it.  DO NOT buy a cheap 10X adapter that screws on to the front of your regular lens: it's a waste of money and time.   I am currently shooting my photos on "manual focus" (MF) at a shutter speed of 1/200th of a second and an ISO of 200.  I need a speed that allows me to get pictures of insects that sometimes move in a hurry without sacrificing "depth of field" (i.e. I want as much of the insect to be in sharp focus as possible).  If there are photographers out there who have more success with different settings, please pass that information along.

4. My "stage": To take most of my shots, I put the insect into a petri dish filled with water.  That helps to confine their movement.  However, it has its problems.  That's because all of these guys immediately head for the side of the dish, meaning the side of the dish ends up in the photo (as with the spiny crawler above).  Still, this can have some interesting consequences: you can, for example, end up with good "reflection" photos as with the humpless caddis below.

What goes under the dish for the "background"?  At the moment, I put my handkerchief under the dish for a lot of my shots.  This gives me texture and contrast, and for most insects seems to work very well.
E.g. the photo of this roach-like stonefly.

Unfortunately, this means I always end up back at my car with a soaked handkerchief and a very wet pocket!  So there are other things that I can suggest.  For example, if you can find some nice colored leaves and/or moss, they can work very well with some photos, as with this Lepidostomatid.

I've also put the dish on top of sand and gravel (Perlodid stonefly, genus Clioperla):

And ice crystals work very well (a large winter stonefly, genus Taeniopteryx):

And if you're out sampling, some insects photograph well in the ice cube tray you're using for sorting (brushlegged mayflies).

In the spring, I imagine there will be grasses and flowers in a lot of my photos.

6. Microscope photography:  While I prefer to photograph at the stream, there are times when things have to be done at home in the lab.  Even a good macro lens can't get a good shot of a tiny, tiny insect -- you must use a scope.  The same is true for photos of the anatomical features that we use for identification.  How do we do this?  Actually, it's not all that hard.  All you need -- in addition to a good microscope, of course! -- is a "T adapter," a gadget that attaches to your camera just like a lens.  It's inexpensive and available on-line.  This consists of a tube that fits over an eyepiece on your microscope, so the eyepiece effectively turns into the lens.   And this is what allows us to get photos like this of the mesosternum of a Perlodid stonefly.

But using a microscope for your photos is not always a snap (sorry, forgive the pun).  It can be difficult getting the lighting correct, and focussing can be a problem.  But the biggest problem I've found is that I often end up with "bright spots" on the photo (there are some in the photo above), which are reflections of the microscope lights.  I always try to "edit" these out -- but my results have been mixed.

"Hidden Streams" and the Quality Insects they Hold

(A "group shot" of a Giant stonefly with a freeliving caddisfly and a green stonefly (Chloroperlid) between its left legs: it's resting its head on the case of a Lepidostomatid caddis [inhabited].)

Today's stream must go unnamed: it's on private land -- but I did have permission to explore it.  It's a high elevation tributary to the Moormans River.  The land is totally forested, and the stream tumbles down a steep, rocky ravine: the water is crystal clear.  And the insects I found are the kind of insects you'd expect to find in a stream of this sort.

1. Stoneflies.  Eight stonefly families were represented in the nymphs that I found: Roach-like stoneflies (Peltoperlidae); Nemourid stoneflies (genus Nemoura); small winter stoneflies; large winter stoneflies (genus Strophopteryx); Giant stoneflies (lots of them); common stoneflies (Perlidae), both genus Acroneuria and genus Eccoptura; Perlodid stoneflies -- Isoperla and Diploperla; and green stoneflies (Chloroperlidae), genus Sweltsa.  Stunning!  The only family I didn't find was Leuctridae (rolled-winged stoneflies).  I have no doubt that I'll see them here later on in the spring.

II. Mayflies.  Only three families -- Heptageniidae (flatheaded mayflies), Ameletidae (Ameletids) and Leptophlebiidae (pronggilled mayflies).   But, as we know, Ameletid mayflies and pronggilled mayflies are only found in very good water, and there were three different genera of flatheads represented: Epeorus (lots of them -- but then it's their season), Maccaffertium, and Leucrocuta.   Again, having multiple genera of flatheads present simultaneously in a stream is, I think, a sign of a very good stream.   (I will have to revise what I said in my entry on "Flatheaded Mayflies" -- 1/8/11-- on the genus Leucrocuta being around mostly in "summer".)

III. Caddisflies.  Many rocks were simply covered with Uenoid cases -- all of them occupied, and I found a couple of Lepidostomatids.    I also found several freeliving caddisfly larvae and a lot of common netspinners, all of the netspinners genus Diplectrona -- which I noted in my entry on common netspinners (1/5/11) has a very low tolerance value.   Note the color, sort of grayish brown, not the "green" we've come to expect with our netspinner friends.

There are two things we look for when we identify this particular genus.  1) It has a "simple" fore trochantin (i.e. not a "forked fore trochantin as we find with the common genera Hydropsyche and Cheumatopsyche).  It's just barely clear in this picture.

And 2), the "meso- and meta-notum [are] divided by a transverse fracture line in the posterior third" (Peckarsky, et.al., Freshwater Macroinvertebrates, p. 101).  Those lines are very clear in this photo.

On the "freeliving" caddisflies -- I've already written about the problem of color (see "The 'Other' Freeliving Caddisfly," ): most people think they're always dark green, and they're not.  In that previous entry I had photos of one that was brownish gray.  Today, I found two additional colors: one was a kind of light, aqua green; the other was a creamy tan.  Here are the photos (and I apolgize for the poor quality of the first).

(Note that the back edge of the pronotum, on both larva, forms a black collar in the shape of an inverted "U".)  When I had this second caddisfly in the tray to take its photo, it was conversing with a green stonefly: I'm not sure the green stonefly realized that freeliving larvae are predaceous!

Some things you just learn the hard way!

4. Photos.  I'll finish with a few photos, since there were so many good pictures to take.

1) A Giant stonefly in the tray in full sunshine.

2) A Giant stonefly that did the "backstroke" for us to show off the tufts of gills that cover its thorax.

3) A lovely Perlodid stonefly, genus Diploperla.  (Later note: This is not Diploperla -- looks like Isoperla, probably Isoperla similis.  9/25/11)

4) And a Perlid stonefly (common), genus Eccoptura.  Note the distinct reverse "T" shape in yellow on the front of its head.

Buck Mt. Creek: Questions, Observations, and Photos

             (A "humpless case-maker" -- Brachycentridae -- and a midge face off in the petri dish!)

Question:  Why am I seeing so many black fly larvae in leaf packs?  This is something I don't understand.  Normally, they've got their bottoms plastered to rocks, bodies and heads standing up in the current, so they can catch their food in their whiskers.  How can they do that when they're inside of leaves?  My only thought is that with the leaves in the water, they're standing up on the edge, but as soon as I take the leaves out of the water, they collapse and roll up into balls.  If someone has a better idea, please let me know.

Observations:
1. There are still a lot of genus Strophopteryx large winter stoneflies around, most of them very large now -- clearly close to hatching.   What I've noticed is -- and this really is an "observation," nothing more than that -- that when the green/yellow striped and mottled large winters (Strophopteryx) get close to hatching, their wingpads lighten in color, turning tan; when the brown/orange striped and mottled large winters (Strophopteryx) get close to hatching their wingpads darken in color, turning dark brown or black.  Pictures below.

2. My second observation is that no matter where I run into small minnow mayflies right now -- and there were a lot of them crawling the rocks this morning -- the genus is always the same: Baetis.   I think the seasonal sequence in all of our streams might prove to be: Baetis (winter/early spring), Heterocloeon (late spring and summer), and Accentrella (fall).   But this may need fine tuning.  We did find genus Baetis in mid-summer last year in Meadowcreek Park -- but they were the "three tailed" Baetis; those I'm finding right now have only two tails.  I would not be surprised to learn that the Baetis small minnows present in Meadowcreek have a higher tolerance value than the Baetis small minnows I'm finding in Buck Mt. Creek and the Doyles River.  Tolerance values are thought to vary by family, genus, and species.  In some lists, for example, Baetis tricaudatus is estimated to have a TV of 1.8; Baetis frondalis, by contrast, has a TV of 8.

I don't think that all genus changes, by the way, vary by season: some depend on the stream.  Thus, in most of our streams the common stonefly we find is, by genus, Acroneuria: but in some other streams (and I'm thinking of Powells Creek in Crozet) the most common genus I see is Eccoptura (and the occasional Neoperla).  One common stone genus that may be determined by season is Perlesta: I've only seen it in streams (Buck Mt. Creek, the Rivanna in Darden Towe Park) in the summer.

Photos:  It was a good day for photos: bright sunlight and, for a change, some cooperative insects who held still for the camera.  So...

1. A water penny beetle, both dorsal and ventral sides (this is the first time I've thought to do a photo shoot of a live one.)

2. A few of small minnow mayflies -- genus Baetis.

3. A midge (Chironomid) who slowed down long enough to get a photo of its front and back prolegs.

4. And finally, a couple of shots of a very pretty Nemourid stonefly, again genus Nemoura.