Freshwater MacroInvertebrates of the Dungeness River

by Victor McAllister

Water quality studies in the Dungeness River at Railroad Bridge Park have turned up many interesting organisms.    Of greatest interest are the insect larvae such as stoneflies, mayflies, and caddisflies, all of which are associated with relatively clean, highly oxygenated water suitable for salmonid fish. 

Insects

Most insects found in the river are immature stages.  These immatures are either described as “larva” or “nymph,” which technically differ from each other.   A nymph is an immature stage that is basically similar to the adults in shape and structure, just smaller and not reproductive.   A larva is an immature stage that differs greatly from the adult. The insect forms listed below have actually been found in the Dungeness by screening or netting.  Other organisms are possible, but not all are confirmed. 

Caddisfly larvae          Caddisfies are often characterized by their “houses” with grains of sand or rock or vegetative matter. Their larvae, if you can coax them from their “houses,” often resemble segmented worms, but they have anterior legs.

Dobsonfly larvae         “Hellgrammites.”  These have six legs and lateral filaments along the sides of their abdomens.

Mayfly nymphs            Most mayflies have three tail appendages, but some have two. They can appear very similar to Stonefly nymphs, but Mayflies have feathery platelike gills prominent along the sides of their abdomens.

Stonefly nymphs          Stoneflies, regardless of size, have two tail appendages and usually no feathery gills along the sides their abdomen.

Cranefly nymphs          Look like a worm, can be up to 4” long, head often not visible because it is

                                    retracted into body.  Fleshy, finger-like extensions at one end.

Damselfly nymphs       3 oar-shaped “tails,” gills at the end of the abdomen, but no gills along sides of abdomen.

Dragonfly nymphs       Fat abdomen and large eyes.

Water boatman            Adult form: front legs shorter than mid and hind legs, propels itself with oar-like strokes.

Black fly larvae           Look like a worm, bowling pin shaped; may be attached to substrate.

Gastropods

Gilled snail                 Has operculum (hard covering used to close the opening)

Pouch Snail                 No operculum. May be spiral shaped in one plane.

Bivalves

Fresh-water clams       Body enclosed within 2 hinged shells.

Worms

Planaria                       Flattened, unsegmented, distinct eyespots, gliding movement.

Nematodes                  Very small unsegmented roundworms, common but often not seen.

Segmented worms       Segmented, earthworm-like body.

Leeches                       Some may look “segmented” but usually have a pronounced “sucker" head.

Crustaceans

Crayfish                       Like small lobsters, large front claw.

Aquatic sow bugs        Armadillo shaped, wider than high, crawls slowly on the bottom.

Scuds                           Like small shrimp, swims fast, on side.

Arachnids

Aquatic mites              Looks like a spider (8 legs) may be very small.