On August 16 of this year, in southeastern Pennsylvania, I stopped at a little "hole" of two-feet-deep water and slow current in a shallow, gravel-bottomed brook that flows under the small bridge I was on to see what aquatic critters would be visible in that hole, which was steeped in sunlight. That deep part of the little waterway was about the size of a pick-up truck and the water was delightfully clear and refreshingly cool on a warm afternoon. And it was edged by tall, bushy pale jewelweed plants that were bearing several yellow flowers, which, in turn, were surrounded by bottomland shrubby thickets and woods.
At first, I saw no creatures in or near the water with my eyes alone, though several each of bumble bees and least skipper butterflies were visiting the jewelweed blossoms. But by using 16 power binoculars, I saw about 20 black-nosed dace of both genders and various sizes. I didn't see them without those field glasses because dace are brown on top, which blends them into the bottoms of the waterways they inhabit. All the dace were swimming into the current just enough to maintain their positions in mid-stream in the hole, while they watched for invertebrates in the current to grab with their mouths and ingest.
As I watched the dace with binoculars, I noticed a school of several inch-long, big-headed, but tapered fish, pecking at the stony bottom of the little waterway. They were northern hog suckers, hatched in the brook I was watching late this past spring.
Northern hog suckers live in clear, clean streams and creeks that have stony bottoms, where these suckers often are associates of dace and stocked trout. And because they can't tolerate silt or pollutants in the water, they are another indicator of good water quality, as are dace, trout, mayfly larvae and other critters.
Hog suckers live among stones and gravel on the bottoms of clear streams and creeks. They are two-toned, mottled brown, which camouflages them in their niche among rocks and gravel. Adults use their big heads and strong snouts to push through and overturn stones, as pigs root into soil and other materials to get food. Suckers use their down-turned mouths to suck up aquatic insects, tiny fish, crayfish, snails and other little creatures that were hiding under rocks and gravel. Hog suckers also consume alga and other kinds of water vegetation off underwater stones. Interestingly, other kinds of fish lurk downstream from feeding hog suckers to snare and eat invertebrates and vegetation dislodged by the rooting suckers.
Most fish species have well developed air bladders that keep them at mid-level in the water. Hog suckers, however, have reduced air bladders, which allows them to more easily remain on stream bottoms with little effort.
While watching the activities of the well-camouflaged dace and suckers in the brook, I saw one, then another and another crayfish walking slowly among the rocks on the bottom of the brook. Crayfish slowly walk forward, but swiftly propel themselves backward with a quick, powerful, forward flick of their tails. That rapid flip of the tail fools would-be predators into mid-judging which way crayfish will go to escape being caught.
Crayfish resemble lobsters, complete with large front claws, but are much smaller than their saltwater relatives. And like dace and suckers, crayfish blend well into stony bottoms of waterways, making them invisible until they move.
Like all crustaceans, crayfish have a shell which is called an exoskeleton. They shed their shells every so often so their bodies can grow, a time when they are particularly vulnerable and hide out most of the time.
Crayfish skulk about carefully on waterway bottoms to scavenge plant and animal material from between and under rocks. They use their front claws to shuttle food to their mouths. Raccoons, mink, herons, snapping turtles and other creatures eat crayfish.
Spawning in spring, each female crayfish carries her eggs and small, white young under her tail until those offspring are old enough to be on their own. By June, many young crayfish are caring for themselves and growing rapidly, if they are not caught and eaten.
I also saw a few water striders, which is a kind of true bug, "skating" on the water's surface of that little hole in the brook. Striders' long feet act like snow shoes, spreading the weight of those insects so they don't break through the surface tension of the water.
Striders are dark on top, camouflaging them against the bottom. They use their pair of front feet to catch land invertebrates floundering on the water's surface.
A couple of metallic-green, male black-winged damselflies fluttered in the sunlight along the edges of this little deep. These damselflies probably were aquatic nymphs in this brook last year until this summer. Damselfly young and adults prey on small invertebrates in their respective habitats.
A half-dozen, two-inch-long bluegill sunfish hovered motionlessly in this pool. Again, I probably would not have seen them without field glasses. They descended from bluegills that spawned in the creek this brook pours into. And they feed mostly on invertebrates and tiny fish.
I got a glimpse of a young northern water snake sneaking along the edges of this pool after small fish and crayfish to eat. The snake, too, was camouflaged, to ambush prey and hide from enemies.
That little hole in the brook is small and limited in kinds of little creatures that are camouflaged in their shared habitat, but big in beauties and intrigues. And, as everywhere, there are lessons in food chains and camouflage in this clear-water habitat.
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