Creatures of Woodland Brooks

     Another one of my favorite habitats to visit in southeastern Pennsylvania in summer is some of the cool, clear, freshwater brooks that tumble musically over rocks in shallow stretches and swirl into deeper, slower pools or "holes", all in the shade of deciduous woods.  Several kinds of creatures live about those crystalline holes with slower currents where they don't have to expend as much energy as they would when coping with swift water.
     The first life I usually see around those stream pools is the intriguing, mid-air dancing of male black-winged damselflies.  Those dragonfly relatives are striking with their iridescent-green abdomens and four black wings they hold upright when at rest on a streamside leaf or twig.  And they are particularly handsome when dancing, with wings fluttering like those of butterflies, in shafts of sunlight in the shady woods.  Those male damselflies are courting females of their kind as a prelude to their spawning in woodland streams.
     Both the thin, brown larval damselflies on stream bottoms and the adults in the air consume small invertebrates.
     Little groups of water striders, which are a kind of insect, "skate" across the surface of stream pools.  Their long feet act like skis to distribute their minimal weight so they don't break through the water's surface tension and sink into it.
     Striders' middle pair of legs work together to row these insects over the water's surface and their front pair catch land invertebrates that tumbled helplessly onto the water.
     Striders are dark on top, which camouflages them against the bottom of streams.  And they are white below, which makes them hard to see from the bottoms of streams.
     Schools of black-nosed dace and individual brook trout, brown trout or rainbow trout live in some of the near-pristine streams and their holes in the cool woods.  All these handsome fish ingest a variety of invertebrates in the clear water.  And they all are mostly brown on top, which blends them into the bottoms of the waterways they live in.  However, mink catch and eat some of the trout.
     Several kinds of small, brownish critters live camouflaged under and between stones on stream bottoms, including Johnny darter fish, crayfish, mayfly larvae, stonefly larvae and water pennies.   All these creatures need good water quality and their presence in a waterway indicates exactly that.        Darters have no air bladders to  give them lift in the water, so they rest between rocks on the bottom of streams where they eat tiny invertebrates and fish eggs.  They move about in short spurts across the bottom.
     Crayfish are a kind of freshwater crustacean that hides among stones on stream bottoms.  They venture out, mostly at night, to feed on decaying plant and animal materials.  Raccoons and mink consume some of the available crayfish.
     Mayfly larvae, stonefly larvae and water pennies, which are round, brown and a kind of beetle larvae, are all fairly flat so they don't get swept away in the current and can slip between stones to hide from fish and other predators in the water.  The mayfly larvae and stonefly larvae eat tiny invertebrates while the water pennies scrape alga off the rocks they cling to.
     As larvae and adults, up to three kinds of lungless salamanders, including red, two-lined and dusky salamanders, live under stones along the edges of woodland brooks and streams where they consume invertebrates.  Not having lungs, these amphibians take in oxygen and expire carbon dioxide through their moist skins and mouth linings.
     Louisiana waterthrushes, which are a species of birds, build cradles and raise young in notches in streambanks in the woods.  And they patrol the stony edges of little waterways in woodlands to pick invertebrates like mayflies and others from under small stones to feed themselves and their young.
     Waterthrushes bob and dance as they walk along the edges of woodland waterways to get food.  I think that rhythmic action is a form of camouflage as they mimic woody debris bouncing in the current along the edges of the waterways.  
     When along brooks and streams in summer woods, look for some of these interesting, little creatures.  They make time in those lovely woodlands more enjoyable.