Monday, January 31, 2011

"Dragons and Damsels": Odonata, Pt. II.

The damsels.  There are three damselfly families: "Broad-winged" (family: Calopterygidae), "Spread-winged" (Lestidae), and "Narrow-winged" (Coenagrionidae).    I have never seen a "Spread-winged" damselfly(Lestidae), and I'm not convinced they exist in our streams, at least in those parts of the streams that we normally sample.  Thus, our only concern in this entry will be the families Calopterygidae and Coenagrionidae.

Damselflies and dragonflies differ markedly in their appearance.   However, they inhabit similar water, both preferring the warm, slow waters along the edges of rivers and streams, and streams with vegetation that grows on the bottom.  They are also both predaceous in their eating behaviour, dropping and extending their lower lips to pick up their prey (remember the photo of the Cordulegastridae nymph from the previous entry).  They are also cannibalistic: they eat their own!  I've seen this with my own eyes both in samples brought into the lab, and while sampling out on the streams.  But damselflies differ from dragonflies in having what appear to be three visible paddle-shaped tails: in reality, these are "caudal lamellae," and are actually gills used for breathing.  (Close-up photo below.)

Calopterygidae (the "Broad-winged" damselfly"):

This is a beautiful nymph:  long, slender, and delicate in appearance.  I've found very small ones -- less than 1/2" in length -- but I also found one that was close to 2" long;  that one is now in the StreamWatch reference collection.  While their thin bodies really give them away, it is the antennae that are used for family identification.  The first segment of each antenna is thicker and longer than all of the following segments.  This can be seen in the photo above, but here is a close-up that focusses in on this feature.

The StreamWatch data available to me suggests that this type of damsel is only found rarely, and most often in the main stem sites of the Rivanna.  Nonetheless, I think we're finding increasing numbers of them and not only in the Rivanna:  on my own stream excursions I've seen them quite often in Buck Mt. Creek and in the North Fork of the Rivanna.  When I find them, they're always in the tangled up vegetation that covers the rocks in the summer.

Coenagrionidae (the "Narrow-winged Damselfly"):

The body and head of the "Narrow-winged damselfly" are obviously wider/larger than those of the "Broad-winged damsel".  Also, the segments of the antennae are pretty well equal in length.  But the key feature to see for identification is the labium (lower lip).  Like the labium of the Darner dragonfly, the labium of the "Narrow-winged damsel" is wide at the top but narrows down at the bottom.

So, these are easy to ID in the field if you flip the nymph onto its back and look at the lip with a loupe.

Narrow-winged damsels are found more frequently in StreamWatch samples than the Broad-winged damselflies.  That's a little too bad since their TV is "9," while that of the Broad-winged is "5".  That being said, they have been found in Ballinger Creek, Buck Mt. Creek, the Doyles River, Lickinghole Creek, the Lynch River, the Moormans River, Swift Run, the South Fork of the Rivanna, and at all of the sampling sites on the Rivanna itself.

As we all know, we see the adult dragons and damsels throughout the hot months of summer.  That means we expect to see nymphs in late spring, all summer, and even into the fall (I found one in November at Buck Mt. Creek.)

Sunday, January 30, 2011

"Dragons and Damsels": Odonata, Pt. I.

Dragonflies and damselflies belong to the order Odonata.  Dragonflies form the suborder Anisoptera; damselflies form the suborder Zygoptera.   I thought I'd address identification of the dragonflies we find in our streams in this entry, then do the same with the damsels in "Odonata, Part II.".

I have seen nymphs of five dragonfly families in our watershed streams: 1) Clubtail dragonflies (Gomphidae), 2) Darner dragonflies (Aeshnidae), 3) Emerald dragonflies (Corduliidae), 4) Skimmer dragonflies (Libellulidae), and 5) Spiketail dragonflies (Cordulegastridae).  I have not attempted to identify the genera of all of these nymphs: I do know that we have at least three different genera of the Gomphidae (Clubtail) family: Ophiogomphus (the Snaketail dragonfly), Progomphus (the Common Sanddragon dragonfly), and Hagenius (the Dragonhunter dragonfly -- also called the "Black Clubtail").

I. Clubtail dragonflies (Gomphidae)

Virtually every Gomphid we see, I think, is genus Ophiogomphus (the Snaketail dragonfly).  I have only seen two that were not.  So, let's begin by noting the defining characteristics of this particular genus.  They are: 1) as with all members of the Gomphidae family, the antennae have four segments, and the third segment (away from the head) is huge in comparison with all of the rest: the fourth segment is small; it may not be visible.  And 2) the wingpads diverge from the main axis of the length of the body.  Let me show you three pictures.

While the wingpads are too small to see in the first photo, and very tiny in the second, we can clearly see how they diverge from the main axis in the third.

The two Clubtails I've found that do not belong to this genus, are both nymphs that I found on my own.  One is genus Hagenius (the "Dragonhunter" or "Black Clubtail").

The third antennal segment is still very large, while the fourth is hard to see.  But the wingpads here are "parallel" to the main axis of the length of the body, and the body is flat, long, and wide.  The ruler shows this nymph to be about 1 1/2" long.  I had no idea what I had found when I came upon this in the Doyles River last summer!

Finally, I have found one Clubtail that's genus Progomphus (the Common sanddraggon dragonfly).  This is a strange looking insect.

This nymph was in a handful of sand I picked up in the Mechums River while doing a geomorphology study with other members of StreamWatch.  With this Gomphid, again the wingpads diverge from the main body axis, and the third antennal segment is clearly the largest, but the fourth antennal segment is really quite large and very visible.  Below is a ventral view of the antennae.

In the DEQ and StreamWatch reckoning of tolerance values, all Gomphids are given a "1".  However,
in the EPA listing of tolerance values by region, North Carolina gives the genus Progomphus a value of "8.7," and Hagenius a value of "4".    StreamWatch finds most of its Gomphids (Ophiogomphus) in 1) its reference sites, 2) Buck Mt. Creek, 3) Cunningham Creek, 4) Long Island Creek, and 5) two sites on the main stem of the Rivanna (Crofton and Rivanna Mills).

II. Darner dragonflies (Aeshnidae)

They're ugly!  Any questions?  Darner dragonflies have long, slim bodies, they're uniformly black or dark brown, and they have short, thin, antennae with six or seven segments.   But the key feature is the labium (lower lip) which is flat (looked at from the side), and wider at the top than it is at the bottom (when looked at from underneath).  This is clear in the following photo.

Darner dragonflies have a TV of "3," and few are found in our watershed streams -- if we can trust the StreamWatch data.  When I go out to streams on my own, however, I frequently find them.  I think the problem is that they do not live in the "riffles" where most samples are taken: they prefer the slow, weed-choked water by the sides of the streams.   I always find them close to the shore.

III. Emerald dragonflies (Corduliidae)

This is an insect we find only rarely.  A few have been found in the North Fork of the Rivanna, and I've found some in the Rivanna itself.  This has a tolerance value of "5".   This dragonfly is closely related to the "Skimmer dragonfly" (Libellulidae); in fact, some keys do not try to distinguish between them.  However, if we go to the "Bible" of keys -- Merritt, Cummins, and Berg, An Introduction to the Aquatic Insects of North America, Fourth Edition, pp. 246-249  -- the two are distinguished by the depth of the "crenulations" (= notches) on the distal margins of the palpal lobes.  On Corduliidae nymphs the notches are deep; on Libellulidae nymphs the notches are shallow.

The "palpal lobes" are the upper, hinged parts of the labium (lower lip), seen here in ventral view.  These notches would be deep in the eyes of Merritt, Cummins, and Berg.  So, this is Corduliidae.
(Please note that I do not have a Libellulidae nymph in my collection: I wish that I did.)

IV. Spiketail dragonflies (Cordulegastridae)

This is another dragonfly we find only rarely.  StreamWatch records one found in the Rivanna River at Milton, and my group found one at the StreamWatch reference site for Albemarle County in the fall of 2009.  It was a big one, and I have a photo of it as it was preserved.

This was about 1 1/2" long.  I have one more in my own reference collection -- but I don't know where I found it.  Still, we can use it to see what is used in defining this family.

The feature on which we need to focus is the lower lip (labium) which in this case has dropped down in front of the head.  (Death was a "jaw-dropping" experience!  Sorry.)  The two "lobes" at the end of the lip are, again, the "palpal lobes," and it's the distal margins of those palpal lobes that are important for us.  Here's a close-up view.

Note the "jagged" edges of those palpal lobes.  That makes this a "Spiketailed" dragonfly.

The "Other" Diptera (True Fly) Families

We've already talked about midges and black flies, the two members of the order Diptera with which we're all quite familiar.   Of the other families in this order -- I have not done a lot with them: my main interest in stream work from the very beginning has been the study mayflies, stoneflies, and caddisflies.   Still, I do have close-up photos of most of these insects and can indicate the main features we use for family identification.  With that in mind...

1. The insect pictured above is a "mosquito larva" (family: Culicidae).  This is the only one that I've ever seen.  I found this last summer in Ballinger Creek when the water was low, when the riffles had essentially turned into pools.  Key features for identification are 1) the brushy hairs in front of the head (the "moustache"?) on either side of the mouth, and 2) the fact that the three thoracic segments are fused to form a large square that is wider than the abdominal segments.

2. This is a "dance fly" (family: Empididae).  These larvae are very, very small and hard to ID in the field.  They have a tolerance value of "6".   The key for identification?  There are prolegs present on abdominal segments 1-8 (sometimes just 2-8).  Those on segment 8 are longer than the rest.

3. This is an "aquatic snipe fly" (family: Athericidae).  It's the only one I've ever seen, and it is not from our watershed.   I found this last summer in a little stream named Back Creek near Lyndhurst, VA.  Using Voshell (A Guide to Common Freshwater Invertebrates of North America, pp. 184-185), you might think that the dance fly and the aquatic snipe fly could be confused.  But note that the tail ends are quite different, and when I picked this one up, I thought I had mistakenly picked up a small crane fly.  The tolerance value is "2".

4. This is a "horse fly larva" (family: Tabanidae): tolerance value of "6".  If you look closely, you'll see that the first seven abdominal segments are encircled by pairs of welts.  There are no prolegs at the end of the abdomen.

5. This is an "aquatic moth" (family: Pyralidae).   It belongs in the order Lepidoptera; it is not a Diptera.  I hope the reader won't mind if I fit it in here.  Note that, as with most other insects, there are pairs of legs on each of the three thoracic segments (head is pointing to the right).  There are also pairs of prolegs on abdominal segments 3-6; they look like crochet hooks with magnification.

6. Finally, one that everyone knows -- the "crane fly larva" (family: Tipulidae).   This has a tolerance value of "3".  As ugly as they are as larvae, they turn into quite lovely terrestrial insects: sort of like Buddha-nature: a lotus rising out of the mud!  The larva pictured above is genus Tipula: most of the time, this is the genus we see.  But we do, on occasion, see two other genera -- Antocha and Hexatoma.

This is the genus Antocha, and note the "creeping welts" on abdominal segments 2-7.   I regret to say that I have no photo to show you of genus Hexatoma.  It's a cool looking larva.  It has a "bulb" on the end that looks like an onion or red beet.  Neither Antocha nor Hexatoma  is commonly found in our streams.

A Note to my Readers

With my entry on "Spiny Crawlers and Nemourids," I have pretty much said all that I've wanted to say about EPT families and genera (EPT = Ephemeroptera [mayflies], Plecoptera [stoneflies], and Trichoptera [caddisflies].   That means that I will probably make fewer posts in the future -- maybe 2-3 a week -- restricting myself to "stream reports" and "phenology" (noting when certain families and genera appear for the first time).

If you wish to contact me with comments, questions, requests, whatever... please feel free to do so by e-mail.  You can reach me at:, or

Let me also say that, being retired, I'm available to help groups in other parts of the state (within reason, of course!) in sampling their streams.  Most of the work that I do, I do on my own -- and I love to explore streams in that way, finding insects and taking pictures.  But I also like working with groups on samples and/or special projects.

Thanks so much for your support of this Blog, and I hope you'll continue to check in as you've been doing.  It's been gratifying to see the number of "hits" I've been getting each day.


Bob Henricks

Oh.  The most popular post?  "The Other Stonefly Families" (1/13/11)

The "Super Hatches" of Spring: "Spiny Crawlers" and "Nemourids"

When I worked with StreamWatch we regularly saw abnormally high numbers of two different taxa in samples done in the spring: "Spiny Crawler" mayflies (family: Ephemerellidae) and "Nemourid" stoneflies (family: Nemouridae).   Nemourids, in fact, simply aren't found any other time of the year (at least I haven't seen them), and Spiny Crawlers are found, but in much smaller numbers (and the genus usually differs from the one we find in the spring.)

Spiny Crawlers:  According to Barbara Peckarsky, -- Freshwater Macroinvertebrates of Northeastern North America, pp. 26-29 -- there are six spiny crawler genera we might find in our streams.  To date, I've only seen three: Ephemerella, Serratella, and Drunella.  Without any question, most of the spiny crawler nymphs that we see in this part of Virginia are genus Ephemerella.  Fly fishermen are very familiar with the name of this genus, since it accounts for three major late spring and early summer Eastern hatches:  Ephemerella subvaria (the "Dark hendrickson"), Ephemerella rotunda and invaria (the Sulphur Duns), and Ephemerella dorothea (the Pale evening dun -- or P.E.D.).   (On the Ephemerella hatches, see, for example, Malcolm Knopp and Robert Cormier, Mayflies: An Angler's study of Trout Water Ephemeroptera, p. 191).  (The photos that follow are both genus Ephemerella.)

The feature that allows us to identify spiny crawlers is the location of their gills on top of the abdominal segments; they do not stick out to the sides of the abdominal segments (as they do with all other mayflies that we have discussed-- Small Minnows, Brushlegged mayflies, etc.).   Ephemerella nymphs have oval, plate-like gills on top of segments 3-7, but the gill on segment 7 is often totally or partially blocked from view by the gill on segment 6.   Thus, when we look at this nymph through a loupe, we normally see only 4 gills on each side of the abdomen -- as in the photo below.  (Note the "spiny" edges on the abdominal segments.)

This same gill arrangement is found in the other genera we're discussing as well -- Serratella and Drunella.  So how do we distinguish the nymphs of these three different genera one from the other?

Ephemerella and Serratella nymphs look much the same.  But, there are three ways to tell them apart.
Number one is a matter of timing.    Serratella nymphs start to show up only after the Ephemerellas are gone.  All of the spiny crawlers I saw last year in the spring were Ephemerella (or Drunella); all that I saw in the summer were Serratella (Serratella deficiens produces the late summer "Little dark hendrickson" hatch).  Number two, at least with the nymphs I have seen, mature Serratella nymphs are quite a bit smaller than mature Ephemerellas, and they tend to be darker in color.  A Serratella nymph is pictured below.

The third feature distinguishing Ephemerella and Serratella nymphs from one another is the look of the tails: Ephemerella tails are covered with many fine hairs (intrasegmental setae); Serratella tails simply have whorls of spines.  They are pictured in order below.

What of the third genus that we see in our streams, spiny crawlers genus Drunella?  Let's take a look at this "odd man out".  The "muscular" front arms are a good clue to use for identification (also note how well the gills show up on top of the abdominal segments.)

Since this is a nymph that stream monitors can find confusing, it's worth looking at more than one sample.

This could be mistaken for a small frog!  But the mistake a lot of monitors make is to put these nymphs in with the flatheaded mayflies based on the size and shape of the head.  The genus Drunella differs from Ephemerella and Serratella -- and all other spiny crawler genera, for that matter -- by the presence of "spines" or "tubercles" on the leading edge of the femurs on the front legs -- pretty obvious in the picture below.

As I peruse the StreamWatch database, I find very few watershed streams that do not have spiny crawlers, and the large numbers in samples always occur in the spring.  The only streams where spiny crawlers seem not to be found -- or found in very small numbers -- are the worst streams sampled by StreamWatch; e.g. Meadowcreek, Moores Creek, and the South Fork of the Rivanna.   I'm quite sure that almost all of the spinys that show up in samples are genus Ephemerella.  My impression is that Drunella and Serratella nymphs live in very few of our streams, and with Drunellas, that would be in pretty good streams.  Drunella nymphs have a tolerance value of 1.0 (or less).  (TV lists do not agree on what value to assign Spiny Crawlers in general, but VA DEQ and StreamWatch give them a value of "4".)  I have found Drunella spinys in the Moormans River, Cunningham Creek, the Lynch River, and Buck Mt. Creek.

Various common names have been proposed for this insect (family: Nemouridae) -- "Spring stoneflies," "Brown stoneflies," "Forest Flies" -- but we find it best to just stick with "Nemourid".   I think of "Nemourid nymph season" as running from March 1 - May 30.   I'm sure that's a little too rigid, still, that's when I normally find them.  Nemourid stonefies are small stoneflies: I doubt they ever exceed 1/2" in length.  They are usually dark brown in color, and one can often see a "Y" pattern on top of the head.
But THE defining characteristic for this particular taxon is the presence of "cervical" gills -- i.e. frilly bunches of gills that stick out from the neck.  Let's take a look.

And here is a closer look at those gills from the ventral side.

(I keep trying to come up with some clever way to describe these:  "whiskers"?  "sideburns"?  Just not quite on the mark!  In any event, they're actually pretty easy to see in the field with minimum magnification -- even with very small nymphs.

But monitors should be aware that we do have two genera of Nemourids that show up in our streams.
The one with the "cervical gills" -- and clearly this is the most common Nemourid we see -- is genus Amphinemura; the genus Nemoura does not have those gills!  Here is a photo of that type of nymph.

I have found exactly two of these in the many excursions I've made to streams in the last few years and in the samples I've taken.  Still, they're there.  And it can be difficult to distinguish this nymph from the large winter stonefly (the wingpads look exactly the same).  To do that you need to see the length of the two tarsal segments, for which you need a pretty good microscope.

Although we find a lot of Nemourids in this watershed in the spring, they are not normally found in the Rivanna itself.  They prefer small to middle size streams, and with a tolerance value of 2.0, they prefer pretty clean water.

Saturday, January 29, 2011

Stream Report: Mechunk Creek near Cismont

I didn't have the best riffle to look in -- but I had no trouble locating nymphs -- lots and lots of stoneflies.  In the short while I lifted up rocks and sorted through leaf packs, I found about a half dozen large Perlodid stoneflies, genus Clioperla -- as in the photo above.  Note that the wingpads are almost fully developed: I'd say the one in the photo above was about 3/4" long.   I also found lots of large winter stoneflies, both genera -- Taeniopteryx and Strophoteryx.  All of the Taeniopteryx nymphs were big, I'd call them fully mature; the Strophopteryx nymphs were all different sizes.

I took some photos of the Taeniopteryx nymphs, and one cooperated nicely by rolling over on its back and lying still.  The photos below are of the dorsal and ventral views of that nymph, and note how clearly the "coxal gills" show up in the ventral view.  They were quite visible to the naked eye.  There is no need to guess about the family or genus ID of this insect!

I also found a Sowbug, and there were still a few small winter stoneflies around: I don't expect to see them much longer.

Finally, a photo to gross us all out: a large colony of black flies.  A lot of the rocks that I lifted were covered with black fly larvae.  In fact, there was no need to pick the rocks up.  You could see them on top of the rocks, bending with the current.  These were all genus Prosimulium.   I reported on another site in the Mechunk on December 15th of last year where large colonies were already in place.  This is one of the streams where they're found in large numbers just about every year.

Friday, January 28, 2011

The "Tiny Mayflies" of Summer: the "Little Stout Crawlers" and the "Small Square-gills"

First of all, for my fellow fly fishermen -- "Little Stout Crawlers" are Tricos!  (family: Tricorythidae)
Wouldn't you think the entomologists would get with it?!  After all, "Trico" is a lot easier to say than "Little Stout Crawler," and it's easier to record on the data sheets monitors use.

Fly fishermen already know these are "tiny".  We all hate them; but we know that we have to have imitations to use come late summer and early fall when they hatch.  Tiny or not, when they're on the water, they're on the water in very large numbers, and the trout like to move through the water sipping them down as they go.  But tying on a size 20 or 22 hook is no easy task for those of us of the "senior" persuasion, and seeing them on the water is even more of a challenge!

Back to the entomology side of the coin.  Tricos have a very distinct feature that, if you can see it, makes identification a simple matter.  They have "triangular operculate gills".  Picture.

These are not so much "gills" as "gill covers."    They cover the "functioning gills" -- i.e. the gills that are absorbing the oxygen.   Since Tricos prefer the slow-moving water in rivers and streams, the "operculate" gills protect the real gills from a build up of silt.   In the StreamWatch data I've looked at, and in my own experience in working with StreamWatch, Trico nymphs are found almost exclusively in sites on the main stem of the Rivanna.

While the Trico ("Little Stout Crawler") is of great value to the fly fisherman, the "Small Square-gill" (family: Caenidae) is of little, if any, value at all.  The "Small Square-gill" is fittingly named since its "square gills" are used for identification.  Here is a close-up.

Note that these gills overlap;  the Trico's triangular gills do not.  Still, these gills serve the same purpose.
I.e. they are there to protect the functioning gills from a build up of silt: the "Small Square-gills" also prefer to live in the slow moving water of streams.   Some lists of "tolerance values" give the Small Square-gill a high value of "7": but StreamWatch has a tolerance value of 4 for both the Small Square-gill and the Trico.

Interstingly,  this mayfly is hardly ever found in main stem sites on the Rivanna.  It is found in a good many streams in our region but usually in small numbers.  Identification in the field isn't easy: this nymph is very small.   But the color pattern is such that when I see it, I see an insect wearing a white belt and shorts!  The Trico gills, on the other hand, look more like "chaps".

Wednesday, January 26, 2011

The "Strong Case-maker" Caddis: (family: Odontoceridae)

The Odontocerid caddis larva (Strong Case-maker) has a tolerance value of 0.0.  That goes a long way in explaining why, in the StreamWatch data I'm using which goes through 2007, exactly 2 larvae are noted as having been found in this watershed's streams.   One larva was found at one of the reference sites, the other in the Doyles River.  On the other hand, I found them by the dozens in November of 2009 in the Rapidan River where it flows out of the National Park.  I guess that's pretty clean water.  They were lying loosely on tops of rocks.

The "Strong Case-maker" gets its name for the straight-forward reason that it makes a very strong case.
You won't break it by squeezing it with your fingers, and in the lab, we tried, unsuccessfully, to break one with metal tweezers.  The bits of rock that make up the case are held together by extra amounts of silk, the silk that caddisflies use to "glue" their cases together.    Thomas Ames speculates that this is done "as protection against the grinding motions of the substrate," in which they spend a good deal of their time (Caddisflies: A Guide to Eastern Species for Anglers and Other Naturalists, p. 209).

Dichotomous keys do note tiny things one can look for when working at identification.  I've never seen any reason to risk eye strain with identification of this particular larva.  Number one, the case is unique (and the "hard" case is one of the features used by the keys), and number two, also distinctive are the black and orange bands on the head.   One other thing that is striking is the clustered gills that cover the abdomen (see below) -- though such gills are not unique to this particular family.

While there is more than one genus in the Odontoceridae family, almost all larvae found are genus  Psilotreta.  This is also an easy identification to make:  with larvae in this particular genus, the front edges (anterolateral margins) of the pronotum come to a very sharp point.  The two pictures below make this point very well.

Odontocerids hatch in May and June in our region.  But they have a two-year life cycle, so they might be found at any time of the year in various sizes and various stages of development.