Aquatic Beetles (Coleoptera)

There is a limit to the types of insects I'm going to find while I'm writing this Blog.  What I discover will almost always be based on trips I'm making to streams on my own, and I'll be looking for insects by lifting rocks and sifting through leaf packs.  That means that I will rarely see insects that spend most of their time in the substrate and/or chewing away on sunken limbs and logs.  So there will be only occasional mention of "beetles" (with the possible exception of Water Pennies and Whirligig Beetles -- on which, more below.)  But let me say a few words about them in this entry since they are important members of the ecological communities in our streams.

Without any question, the beetle family we see most often is the Elmidae family -- Riffle Beetles.
We see the adults (fully aquatic) and the larvae.   Pictured above is a Riffle Beetle adult -- but remember, this is a highly magnified image.  In reality, Riffle Beetle adults are rarely bigger than a grain of pearled barley and can be the size of a grain of couscous (i.e., they're barely visible on the net).  A distinctive feature of this beetle is the antennae: they are long, and often reddish in color.  These can usually be seen with a loupe.  Riffle Beetle larvae are commonly referred to as "comma bugs," and the photo below shows us why.  When put into a sampling tray, they often curl up in this fashion.

We find Riffle Beetles, both adults and larvae, in almost all of our streams, but they are more numerous in some rather than others, this is especially true of some of the streams in the southeastern part of our watershed (Fluvanna County: Raccoon Creek, Ballingers Creek, Long Island Creek).  I don't know why this is the case.  Perhaps someone else can explain it. (Comments are welcomed.)

Many (most?) of the samples done by StreamWatch this fall were dominated by Riffle Beetles.  We have a strong suspicion that this is related to the bad drought conditions we had most of the summer.
By September, if not before, a lot of our streams had simply dried up and stopped running.  Mayfly, stonefly, and caddisfly nymphs were very scarce in our initial fall samples (did they die off?  or did they save themselves by digging deeper into the substrate?).   But Riffle Beetles -- and some of the other beetles as well -- seemed to survive the drought very well.

The Dryopid (Long-toed) Beetle is close in appearance to the Riffle Beetle adult, and the two can be confused by samplers.  But Dryopid beetles are always larger than Elmid beetles, and they have only short, stubby antennae (visible in the photo above).   In the photo below, I've placed the two side-by-side -- Riffle Beetle on the left, Dryopid beetle on the right -- so the reader can get a sense of comparative size.  But remember, this is still a "microscope" picture.

 After Riffle Beetles, the second most common beetles we see are Water Pennies (family: Psephenidae).
The name seems fitting given their shape and color.  In the photos below, upper left is the dorsal side of the beetle; lower right is the ventral.

Water Pennies may get as big as a pea (though they're flat), but they are often the size of tiny brown dots on the net.  Water Pennies are "scrapers" when it comes to their mode of eating.  Thus, they are always clinging to rocks, moving slowly over the rock surface, grazing algae and periphyton as they go.  They too survived the drought well.

There are four more beetle families that we see in our streams, but it is rare that we see them.  One is the "Toe-winged" Beetle (Ptilodactylidae) -- which can be mistaken for a very large "comma bug." In the photo below, with the "comma bug" placed at the top, we can get a sense of their relative size.

Only two-thirds of the Toe-winged beetle is showing.  Toe-winged beetles can be as long as 3/4"; comma bugs are rarely more than 1/4" long.  Also, although this picture does not represent this, the Toe-winged beetle is often a yellow/orange color.  We have found these, in very small numbers, in only a few of our streams.

Water Scavenger beetles (Hydrophilidae) are somewhat more numerous, but found mostly in large rivers -- like the main stem of the Rivanna.  There are two types of Water Scavenger beetles, and as the pictures below reveal, they are quite different in appearance.

The Whirligig Beetle (Gyrinidae) is one I've seen in only two streams: Buck Mt. Creek and Mechunk Creek.  In both cases, I've found them in the summer (this is the larval form of a terrestrial insect), and they prefer to live in the matted vegetation that grows on some of the rocks.  They move quickly, and you have to be adept with the tweezers to grab them.

Finally, rounding out the list of beetles we find in our streams is one that we hardly ever see, the Predaceous Diving Beetle (Dytiscidae).  I've found only one (this one) in my explorations.  That was last fall in a small stream that runs along Reservoir Road (coming down from the Ragged Mt. Reservoir).  These are predators -- as are Water Scavenger beetles and Whirligig Beetles -- and they've been known to go after small fish!

Stream Report -- Buck Mt. Creek (+ Black Flies, Pt. 2)

Yes, it was freezing cold this morning, and yes, I had to break through thin sheets of ice moving out from shore into the riffles -- but, the quest for knowledge must go on!  While I found only one small winter stonefly today, and one Taeniopteryx large winter stonefly, I found a lot of Strophopteryx large winter stoneflies (on the two genera, see previous entries).   Most of these nymphs were small, but some are starting to grow and showing their characteristic colors (as the one in the photo above -- live shot).
Has the tide started to turn?  There is always a time when we see fewer and fewer Taeniopteryx nymphs and more and more Strophopteryx nymphs, and perhaps things are moving in that direction.

I also found some netspinning caddisflies, a fingernet caddis, and a fair number of Uenoid case making caddis.  And, I saw a fair number of black flies at this particular site (all genus Prosimulium -- the "good" kind).   But although they were in clusters of 6-8, they certainly were not formed into "colonies."  This is a stream where I have seen large colonies of black flies the past two winters, so this is something I will certainly follow as the winter proceeds.

I thought I might say a word or two about the interesting anatomy of the black fly (full profile view above)  since we see so many of them during the winter.  The photo above makes it obvious why stream samplers call them "bowling pins": they could also be called "velcro butts"!  Black flies have velcro-like projections on their rear ends with which they attach their bottoms to rocks.

They then stand straight up (well, they're slightly bent over) into the current to feed.  In terms of their "Functional Feeding Group" (FFG), they are known as "filter feeders" (or filter collectors), and they collect microscopic bits of food in what look like "bushy whiskers" -- called a "labral fan".  The labral fan is actually quite an elaborate thing, as the reader can see from the photo below (which is looking down from the top of the head).

Common Stoneflies (family: Perlidae)

The most common stonefly we see is the "Common Stonefly" (family: Perlidae), and the most common Perlid genus we see is Acroneuria -- pictured in the photo above.  This is a beautiful stonefly: here is another photo; an Acroneuria stonefly with slightly different colors.  The tufts of gills behind each leg that distinguish Perlid stones from Perlodid stones are pretty clear in this photo.

The Common stonefly nymph, when mature, is a fairly large critter.  Both of the photos above are "live" photos taken at streamside with a macro lens: the actual size of each of these nymphs was slightly over an inch, but I've seen Perlids that are closer to two inches in length.   The Common stonefly is the only stonefly we can find in our streams anytime of the year.  Almost all insects are "univoltine" -- that is to say, they have a one year life cycle.  Perlid stoneflies, on the other hand, can take up to three years to mature.  Thus, at any given time of the year, there can be three generations of Perlids present in our streams, and we can find Perlids in the same sample that vary considerably in size.  Perlids hatch in mid-summer (the "Golden Stonefly hatch" to fly fishermen), so it is not unusual to see the largest Perlid nymphs in late winter and spring.

I have found five different genera so far in our streams, though not all genera seem to be found in all streams.  If there is only one genus present, it is likely to be Acroneuria.  Mature Acroneuria nymphs are often easy to identify by the yellow "M" on top of their heads (very clear in the first photo above).

Also common in some of our streams is the genus Eccoptura which also has a distinct pattern on the top of the head: the front part of the head is yellow and shaped like a drooping "T".  I have found a fair number of these in Powells Creek near Crozet.  Powells Creek in Crozet is also the only stream in which I have found the genus Neoperla (head pictured below).  This genus varies from all other Perlid genera by having only two ocelli (the black dots on the head) instead of three.  (Check it against the Eccoptura picture.)

Are certain stonefly genera "stream specific"?  Is there something about the size of the stream or the type of habitat which determines which genera one will find there?   Are there more genera found in our really good streams than in our so-so streams?  I don't know the answers to these questions; if someone out there does, please feel free to comment.

This is another genus that I have only found in one stream -- and it is not in our watershed.  This Common stonefly is genus Paragnetina, and I have only found this genus in the Rapidan River where it flows out of Shenandoah National Park (another live photo: note the bushy gills behind each of the legs).  This is a genus of stonefly that is very intolerant of stream impairment.  Is that why it is only found in this very clean stream?  (I should add that of all of the insects we study, stoneflies are the least tolerant of impairment: TV's (tolerance values) range from 0-2 on the scale of 10.  Paragnetina nymphs share a feature with Neoperla nymphs that is not found on Acroneuria and Eccoptura specimens.  They have a very distinct "occipital ridge" at the back of the head.  This is a line of close set dark hairs or spinules (clearly seen in the photo below).

Finally, there is one genus that I have only seen in two streams -- the Rivanna River at Darden Towe Park, and Buck Mt. Creek -- and I have only seen nymphs that are fully mature (in May and June).
This genus is very distinct in its colors, with the dark edges on both sets of wingpads.

The photo below shows the distinct Perlid gills -- behind each set of legs.  Rose Brown of StreamWatch calls these -- quite fittingly -- "hairy armpits"!

Perlodid Stoneflies (family: Perlodidae)

There is no common name for Perlodid stoneflies -- though fly fisherman refer to the adults as "Yellow Sallies" (the adult is either pale green or pale yellow).  This is a nymph that, in the field, can be confused with a "Common stonefly" (family Perlidae), even by experienced samplers.  The two nymphs have a similar overall shape, and both can be quite colorful.  But, the Common stonefly has bushy gills behind each of its legs; the Perlodid has none (it's "clean shaven" as it were).  The Common stonefly's gills can usually be seen with a loupe (magnification).

The nymph in the photo above is genus Isoperla and, in my opinion, it's one of the prettiest nymphs we see in our streams.  Nymphs this size normally show up in our samples in mid to late spring -- April and May.  The stripes on the abdomen are a dead giveaway for Perlodid identification (but they might not be visible without magnification).   It is my impression that Isoperla Perlodids are relative "late bloomers": Stewart and Stark (Nymphs of North American Stonefly Genera: Plecoptera, 2002) note emergence dates of June through mid-August in one study conducted in Alaska.

Perlodid nymphs -- I think I'm right in saying this -- do not show up in samples done in the fall (and rarely -- if at all -- in those done in the summer).  I started to find very small Perlodid nymphs this year in samples done in early November.  To date, I have only seen two genera (Peckarsky et.al., Freshwater Macroinvertebrates in Northeastern North America, list a total of 12 Perlodid genera).  The genus I'm seeing the most is Clioperla (the photo above left shows a mature Clioperla nymph).   Anatomically, Clioperla and Isoperla nymphs are very close, but if the nymph is large enough, the head pattern of the Cliopera nymph gives it away.  As we can see in the head close-up above, there is a dark margin at the front, back, and sides of the head surrounding a region of yellow.

The other genus I'm seeing right now is Diploperla (this one was found two weeks ago; the wing pads are not fully developed).   This genus cannot be identified in the field; that requires microscope work at the lab.   For those of you who REALLY want to know what makes a Diploperla nymph Diploperla -- the lacinia is very distinct, and the Y-arms of the mesosternum are incomplete (!).

I am anxious to see if trips afield throughout the winter will reveal other Perlodid genera in our local streams, and to see when Isoperla nymphs begin to appear.  My guess at the moment is that the pale green and yellow adults fishermen see hatching in April are Clioperla and/or Diploperla.

Moormans River off Sugar Hollow Road -- report

I found a number of large winter stoneflies -- both Taeniopteryx and Strophopteryx -- including this very orange specimen (Taeniopteryx).  But small winter stoneflies far outnumbered the large.  The small winters in this particular stream were very small and immature, in contrast with what I've been finding in streams like Buck Mt. Creek (and elsewhere).  Why?  I suspect it has to do with the fact that the Moormans is very close to, or in, the Bude Ridge Mountains.  All fly fisherman know that a hatch always begins in the lower part of a stream then gradually moves upstream.  Thus, we might expect to find insects in earlier instars when we get this close to the source of a stream.  Is this because the water is colder upstream and food sources diminished?   In addition to the winter stoneflies, I found one Perlodid stonefly (genus Diploperla) and two Perlid (Common) stoneflies (genus Acroneuria).  All of the stoneflies were in leaf packs.

I found only one mayfly: this very small Spiny Crawler (Ephemerellidae: actual size, about 1/8").  While it's hard to determine genus in this early stage, I suspect this is Ephemerella:  we find huge numbers of Ephemerella Spiny Crawlers in our streams throughout the spring, most hatching by the end of May.  I also found one black fly -- genus Prosimulium.  All of the black flies found in this stretch of the Moormans in early November were genus Simulium (on the difference between the two genera, see the earlier entry on "Black Flies".

On the bottoms of rocks, I found Uenoid caddisflies, common netspinner caddisflies, and a couple of Saddlecase maker caddisflies.  One of these is pictured above: upper left shows the ventral side of the case, with the head and tail of the larva sticking out from the ends (hanging over the "saddle"); lower right is the dorsal view of the case.  When the case is attached to a rock, the caddisfly cannot be seen.  Stream samplers rarely get to see this caddisfly in its case.  When distrubed, it quickly abandons its case. Thus the larva alone shows up on the net (closeup of the larva below).   The Saddlecase maker is the only case making caddisfly to abandon its case and build a new one as it passes through instars, getting larger and larger.  Most case makers simply add material on their cases.

Midges

The midge is one of the most common insects we find in our streams -- and we often find them in large numbers.  The largest numbers seem to show up in spring and fall samples, but they are present all year long, and the largest numbers tend to be found in the poorer  quality streams.  In our worst streams, they can dominate the sample, along with common netspinning caddisflies.  They are often very tiny (the photo above was shot through a microscope), so tiny in fact that untrained eyes won't see them at all on a net.  They often give their presence away by rapidly wiggling in an "S" shape when they are squirted with water.

But the midge in the photo above -- what most stream monitors mean when they refer to a "midge" -- is only one type of midge that we find in our streams.  This is a "non-biting midge," family Chironomidae; many fly fisherman, in fact, refer to them as Chironomids.  Most Chironomids are light yellow to clear in color, but we also see red, green, and black Chironomid midges.  They are highly tolerant of stream impairment, normally given a value of "6" on a scale of 1 (intolerant) to 10 (very tolerant).

The other midges we find in our streams are 1) "biting midges/no-see-ums" (Ceratopogonidae), 2) Dixid midges (Dixidae), and 3) Net-winged midges (Blephariceridae).

Biting midges (Cerats) are thinner and longer than Chironomids; they also lack prolegs, and the head is long and pointed.  They are often "zebra" colored, i.e. segmented in black and white.   Although most tolerance scales also put them at "6," I've only seen them, to my surprise, in our very best streams -- i.e. the "reference streams" used by StreamWatch.  I'm not sure what to make of this (???).

Dixid midges (family Dixidae) are rarely seen in our streams: I've only seen them in three locations;
1) the StreamWatch reference site for Albemarle County (which will remain unnamed), 2) Whippoorwill branch of the Mechums River, and 3) the small stream that runs through Greene County park.  These
are good streams, and Dixid midges are very intolerant of impairment (TV's of 1-3).

These are "Net-winged midges" (Blephariceridae) -- again highly magnified.  As with Dixid midges, these are found in very few of our streams, and they too have low tolerance values (in most scales, a value of less than 1).  I've found them -- always in the winter, by spring they're pupating -- in the Doyles River, the Lynch River, and Buck Mt. Creek.  The photo above shows the dorsal view on the left and the ventral view on the right (head to the bottom in both cases).  The little "suckers" on the ventral side of this midge are used to keep it attached to rocks in fast flowing water.

Lickinghole Creek: Uenoid Caddisflies

I saw a good number of insects in Lickinghole Creek (near Crozet) yesterday -- but it was pretty much "the usual suspects": e.g. large winter stoneflies (both Taeniopteryx and Strophopteryx -- mainly the former) and  small winter stoneflies, a number of very large midges (Chironomids), a fair number of common netspinning caddisflies, and a few brushlegged mayflies.   But I also saw a large number of Uenoid case-making caddisflies, and they are increasing in size from my first sighting (last week at Buck Mt. Creek).

Cases of the caddis family Uenoidae often show up in our streams in early December, when their cases can be very small  (1/8"?): they look like compacted grains of sand that are stuck on a rock.  They can be prolific, with 10, 12, or more cases stuck to a single rock in a stream, but they are normally only found in small to mid-size streams (10'-30' wide); I have never seen them in the main stem of the Rivanna.  Their cases are made from grains of sand and small pebbles, but typically there are 3-4 larger pebbles attached to each side of the case (as in the photo above).   Cases can be colorful or drab, depending on the mineral composition of the stream in which they are found.  By February, they start to seal off both ends of their cases for pupation, often clustering together in large numbers -- 30-40 cases might be seen side-by-side on a rock.

(A young Uenoid that has slipped out of its case.)   Identification of the Uenoid cannot be determined for sure in the field.  However, since we know this is the most common case that we see in the winter in our streams, we tend to know what they are right away.   But Uenoid caddisflies can be confused with certain genera of Limnephilid caddisflies (Northern casemakers) who make a similar case out of pebbles and stones.  (Until recently, the family Uenoidae was considered to be the genus Neophylax in the Limnephilidae family.)  Exact determination requires microscope work in the lab.

There are two anatomical features that make a Uenoid a Uenoid.  They are 1) a "medial notch" in the anterior margin of the mesonotum.  In the photo above, that's the "W" shaped notch in the top edge of the brown, rectangular sclerite between the second set of legs.  (There is no such notch on the mesonotum of the Limnephilid caddis.

And 2) there is a "T-shaped" sclerite on the underside of the head on a Uenoid caddis: in the photo above, this is directly in the center.  For some beautiful photos of the terrestrial form of this insect, the reader is advised to consult the book by Thomas Ames Jr., Caddisflies: A Guide to Eastern Species for Anglers and Other Naturalists (Stackpole Books, 2009), pp. 257-262.

Small Winter Stoneflies (Capniidae)

Small Winter stoneflies are "small."  In the picture above the relatively mature nymph is almost exactly 1/4" long (not counting antennae and tails); the immature nymph, more like 3/16".  We find these nymphs in our samples from October to February: the last nymph I found last winter was on February 19, the first one I found this fall was on October 24.  In other words, their presence in our streams corresponds closely to that of the Large Winter stoneflies, genus Taeniopteryx.  Small Winters hatch from November through February, though I've seem some terrestrials as early as October.

Field identification of Small Winter nymphs, especially with immature nymphs where the wingpads are not fully developed, is difficult and probably should not be attempted.  They are easily confused with Green stonefly nymphs (Chloroperlidae) and with Rolled-winged stoneflies (Leuctridae).  All three are tiny, yellow in color, and they have long, thin abdomens.  Identification can even be difficult with a microscope in the lab.  What must be detected are what are called "ventrolateral pleural folds" (see the photo below).  With Small Winter stones, these can be seen on abdominal edges of segments 1-9; on Rolled-winged stoneflies, they're only found on segments 1-4.

Field identification is easier to do once the nymphs are mature and the wingpads can clearly be seen.  The primary wingpads are long and thin; the secondary winpads are short and stubby.  And, the secondary wingpads sometimes have a notch in the bottom edge of the pad (as in the photo below: this is genus allocapnia).

While immature nymphs are very plain looking with few distinguishing features, the mature nymphs can be very colorful and highly patterned.  The one pictured below is probably not far from hatching.  The terrestrial form of this stonefly is uniformly dark brown or black and unattractive -- something that does not seem to bother the Trout!

Large Winter Stoneflies (genus Strophopteryx)

The other genus of Large Winter stonefly I have seen in our streams -- at least to date, I have only seen two -- is Strophopteryx (on the genus Taeniopteryx, see the entry for December 16).   Strophopteryx nymphs appear later than Taeniopteryx nymphs: my first sighting last year was on December 28, this year I found them as early as December the 8th.  In December the nymphs are still very small; fully mature nymphs can be found from late January into March (by February, most Taeniopteryx nymphs have hatched).

They differ markedly in appearance from the Taeniopteryx nymphs.  They are yellow, with brown or green markings. The horizontal stripes on the abdominal segments can be seen with the naked eye when the nymphs are fully mature, as can the "mottled" patterns on the wingpads and pronotum (see photo above: this photo was taken in March of this year).

Strophopteryx nymphs do not have "coxal gills."  Rather, the distinguishing feature on this genus of large winter stonefly -- in addition to the colors and patterns --  is called the "ventral, triangular, apical plate".  This feature can clearly be seen on this young Strophopteryx nymph.  It is the plate that sticks out from the end of the abdomen on the ventral side -- right above the base of the tails.

Here is a closeup of the feature in question.  While Taeniopteryx nymphs can often be identified in the field using a loupe to see the gills, Strophopteryx nymphs are often difficult to distinguish until they are fully mature.
Oh, one more thing.  When Strophopteryx nymphs are preserved in alcohol, they always -- well, almost always at least -- curl up in the shape of a "C" as in the second photo above.

Large Winter Stoneflies (genus Taeniopteryx)

Stream monitors tend to sample streams very little during the winter -- if at all.  It's not very pleasant, of course, sloshing through near freezing water and sitting in snow banks and counting bugs!  Nonetheless, there is a lot to see in our streams from November through February, things that many monitors miss.  Many mayflies, for example, make their appearance as very small nymphs in late November and/or December -- e.g. small minnow mayflies and spiny crawlers -- and they get bigger and bigger as the winter proceeds.

Another thing that is commonly missed is the chance to see the beautiful large winter stoneflies (we have two genera in our streams, Taeniopteryx and Strophopteryx, this article will only deal with the first).  Taeniopteryx nymphs appear in our streams around mid-October, reaching maturity in January and February when they hatch into their terrestrial form.  The top photo above shows a mature nymph from a stream in January this year: below it is a tiny nymph (actual length, 1/8") that we found on October 24.  When mature, these nymphs are easy to spot -- dark brown in color with a light stripe that runs from the thorax to the end of the abdomen.  But the "defining features" of a Taeniopteryx nymph are the "coxal gills":  long, clear, finger-like projections that stick out from the base of each leg. (second photo above -- very enlarged).

Large winter stoneflies molt numerous times as they mature.  The photo below shows a Taeniopteryx nymph found in late November -- a "teenager," if you will.  If you look closely, you can see the "coxal" gills in clear view behind each of the legs.