Yesterday I stopped at a shallow, two-foot-wide trickle of clear, cold water running a few feet from, and parallel to the farmland road I was on in Lancaster County, Pennsylvania. I stopped because I saw a few male black-winged damselflies fluttering buoyantly together in a streak of sunlight, surrounded by shade, above the tiny waterway. And I wanted to experience animal life in a rivulet in local cropland. This trickle was lined on both sides by jewelweed and grass, and shaded by a row of willow trees planted on the other side of the rivulet from the road in an agricultural area.
Several male black-winged damselflies were along a 50 yard stretch of that tiny waterway, and each one was handsome with his four black wings and iridescent-green abdomen that glistened in the sunlight. Those males seemed to be dancing among themselves over the water, but were really displaying their qualities to other males of their kind to see those rivals off "their" part of the waterway. Winning males have the right to mate with any female that comes into their respective territories. Each damselfly has its favorite perches on plant leaves hanging over the water where each one watches for potential rivals and mates to come along in flight. Each damselfly stays right along its birth brook during its adult life and spawning in its rivulet.
Female black-winged damselflies are a bit thinner and not as brightly colored as the males, which camouflages them better. And each female has a tiny, white dot on top of each wing, all of which are held upright.
While watching the male and female damselflies flutter daintily like butterflies, I saw a little school of black-nosed dace (minnow-like fish) swimming as a group in each one of several deeper, slower-current "holes" in the rivulet. Dace like those holes so they have easier swimming into the current while expending less energy to do so.
Dace are up to two inches long and brown on top, which blends them into the mud or gravel on the bottom of a waterway. They have long, stream-lined bodies for easier passage into currents of water. And each dace has a black stripe along the length of each flank, from nose to tail. Breeding males in June have orange fins and an orange stripe along each side, paralleling the black one.
Both living in habitats of cold, clear water, damselfly nymphs and dace have characteristics in common. Both species were born in small waterways and are brown when living in the water, which camouflages them. Each kind developed ways to deal with constant currents. Dace are streamlined, and damselfly larvae are flat to hide under stones on stream bottoms. Dace and damselfly larvae feed on tiny invertebrates, the dace in mid-stream and damselfly nymphs on mayfly larvae, for example, on stony bottoms. Adult damselflies, however, catch flying insects over the water.
Damselfly larvae have four stages of development in their lifetime. They hatch from eggs among stones on the bottom of cold, clear brooks and rivulets. They feed on invertebrates while they are larvae under the gravel, they metamorphosis and emerge as winged adults ready to fly. They, and many other kinds of insects, pass through those four stages of life so the adults have wings to be able to travel much farther than they could as larvae to find food and mates.
Dace and damselflies are preyed on by other kinds of animals. Dace are eaten by trout, if present, northern water snakes, belted kingfishers and green-backed herons, while their eggs are consumed by crayfish, aquatic salamanders and damselfly nymphs. The larvae of damselflies are ingested by crayfish, aquatic salamanders, and trout, if present. Some adult damselflies are eaten by small birds and dragonflies.
Black-winged damselflies and black-nosed dace have much in common. They are striking, interesting creatures that live in small waterways, including here in Lancaster County cropland.
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