The Wandering Naturalist

 For the next few weeks you’ll be hearing from me while I am on the road.  Some might call this jaunt a vacation, but a naturalist vacation is usually a busman’s holiday. I’ll continue to do what I always do and see what the regional scene offers.  My ability to check in will depend on our ability to connect to a local internet server from time to time, since we are camping on this trip.  My blogs will be short and (hopefully) sweet and will be based on a series of photos. Think of these sessions as a series of postcards sent home by your wandering naturalist.

Crossing Under the Potomac

  The mighty Potomac River cuts a 385 mile path through the mountainous country from Fairfax, West Virginia to the tidal flats of Point Lookout, Maryland. It is primarily a west to east flow, so it is not surprising that we had to cross it several times on our journey to and from the Outer Banks. Since everyone crosses “over” the Potomac (George Washington had his portrait painted while doing so) I thought it would be nice to cross “under” it for a change. Actually a better way to put it would be to “peek under” the waters of this great stream and see what lives there.

  The low sloping banks of the river are easily accessible at Fort Fredrick State Park on the Maryland side. At this point the river is near to its source and has carved a gentle arc through the hills. Here it is a wide shallow pebble bottomed stream with a strong steady current. High sand banks and stacks of drift wood give testament to periods of high water and scouring floods. Back during the canal building craze of the early 1800’s, the Chesapeake & Ohio Canal was dug along a good portion of the Potomac’s route to provide transportation of goods from the east coast to the Ohio River drainage. The canal bypassed the unpredictable river and took advantage of the valley it created. In the end, floods and railroads finally rendered the canal obsolete. You cross over one of the old canal locks on the way into the park and are constantly reminded of the railway’s victory by the rumble issuing from the well used train tracks across the river.

  I walked along shore on the pavement of rocks exposed by low water.  A beautiful little damselfly called the Rubyspot (whose inner wings are bright red) called my attention to the life just below the rippled surface. It landed skittishly on an exposed rock but quickly flitted away upon sensing my presence. Damselfly nymphs are aquatic, so I took this as a clue to look in the water and under the river stones to seek a calmer version of the damselfly.

  The first rock yielded a spritely crayfish that dashed off in a cloud of slit.  I caught it with my left hand and scooped it out of the water.  I’ve gotten pretty good at holding things with my left while I photograph them with my right hand held camera.  You’ve certainly seen enough of my fingers in the pictures sent back from this trip.  To capture an image of the crayfish, I invented a new grip – which I’ll call the Lateral Potomac Crustacean Restraint – to fully expose the whole creature (look here).  The L.P.C.R. hold enabled me to show you the young mudbug in full profile.  You’ll note that crayfish have tiny claws on their feet as well.  The larger pincers do the heavy work and the leg pincers do the delicate pick up tasks. 

  I don’t know the species name, since crayfish look very much alike across the country, but I can tell you it was a male.  An underside view (see here) reveals several sets of swimmerets under the tail section which are used to, well….swim a little (thus the name). The large uropods, or flippers, do the major back swimming work.  Located just after the last set of true legs, the first pair of swimmerets are actually called claspers. They are used by males to “clasp” the female during mating.  My little “crab” was finally able to restore some sense of personal dignity after I released him back to the water.  There he took up position next to rock and dug in to resume his private life (see here).

  The next rock produced a large damselfly nymph clinging to the underside.  Although this wasn’t a Ruby spot nymph, it was a nice one (look here to see it being held using the Potomac Palm Puddle Method).  There in the wrinkled pink folds of my palm, the robust larvae displayed three leafy appendages coming off the end of its abdomen.  These are the gills.  Many of the damselfly nymphs that come from still waters tend to be gangly with long delicate gills and lanky legs, but this one exhibits the traits necessary to survive in quickly moving water.  Short gills and legs combined with a flattened and somewhat streamlined body equip this baby damsel to live in the water flow without being swept away.  As a predator that seeks out other insects for a living it would be very embarrassing to be swept away right at the “Gotcha” moment. 

  In retrospect, I think this damsel is probably a type called the Blue ringed Dancer, but with some 30 species of damselflies along this stretch of the Potomac, I’ll withhold judgment (though I know it leaves you in terrible suspense!).

  A few rocks later, I revealed an even more streamlined insect in the form of a mayfly nymph (see here).  Not only will you note that I elected to keep this creature attached to his native rock underbelly rather than give it the Palm Puddle treatment, but you can also appreciate how tightly it grips that surface.  Mayfly nymphs are herbivores that graze algae and other particles from the bottom stones.  Unlike the damselfly, the gills are located along the sides of the abdomen. The long feelers extending out from the abdomen are for motion detection (for detecting, say, a sleek damselfly nymph approaching from downstream). 

  As to when this mayfly may fly, it likely will emerge from the current sometime next spring.  When it does, it will crawl out of the water and shed its aquatic ways by shedding its larval skin. Many of the exposed surfaces of the river rocks were covered with the shed skins of recently emerged aquatic insects (see here). I think these skins are damselfly sheds.

  Perhaps the most aqua-dynamic of the down under set of the Potomac are the Water Pennies. These critters are easy to overlook when a rock is flipped up for view.  Take a look here and you’ll see what I mean.  and here at a more detailed view. Water Pennies look more like ancient trilobite fossils than recent living beings – that is until they move.  This insect is the larvae of a rather plain looking non-aquatic beetle.  The head and legs are concealed underneath a segmented limpet like covering.  Water flows evenly over the armored back and creates a suction that keeps the water penny clinging to the rock surface.  When Washington threw his quarter over the Potomac before his crossing, the bottom was already coated with pennies.

  Later in the evening, I watched a swimming mink make his crossing of the Potomac and viewed a pair of Quachita Map Turtles feeding on snails.  The turtles half swam- half crawled headfirst into the current with their backs just below the surface.  Their passage was marked by a shadow of ripples on the surface that glinted in the last rays of the setting sun.

  One reason to take a trip under a river – any river – is to monitor its health.  Damselflies, Mayflies, Map turtles, and Water Pennies are all signs of a healthy stream with lots of oxygen and good flow. Though sunset drew my day to a close, I could leave knowing that this mighty river flowed on in relative health.