Small creatures tell big stories about stream health

STARKVILLE, Miss. -- On a hot July day, a shallow creek can look quiet from the bank. Water moves over rocks and around roots, stirring patches of sand and leaves. But just under the surface, there is often a whole world going about its business.

Turn over a submerged rock, sift through a wad of leaves, or look closely along the streambed, and you may find small insects, snails, worms, crawfish and other animals moving through the water. Some may be familiar. A cranefly larva will grow into what many folks call a mosquito hawk or skeeter-eater. A mosquito begins life in water before it ever becomes a nuisance on the porch.

Crawfish, of course, hardly need an introduction in Mississippi. These small creatures are part of the stream’s wildlife community, and their presence or absence can provide clues about the condition of the water and the habitat around them.

These animals are called macroinvertebrates. The word sounds technical, but the idea is simple. “Macro” means they are large enough to see without a microscope. “Invertebrate” means they do not have a backbone. In streams, this group includes aquatic insects, snails, mussels, worms, leeches and small crustaceans like crayfish.

Many of the “bugs” that people find in streams are actually young insects living the aquatic part of their life cycle. Mayflies, stoneflies, caddisflies, dragonflies, midges, mosquitoes, craneflies and beetles may begin life in the water as eggs, larvae or nymphs. Some spend only a short time there, while others may live underwater for months or even years before emerging as winged adults.

During that time, they feed, grow, hide from predators and use the stream’s rocks, leaves, wood, roots and sediment as habitat. Some scrape algae from rocks. Some shred fallen leaves. Some filter tiny particles from the water. Others are predators themselves. Together, they help move energy through the stream food web and provide food for fish, amphibians, birds and other wildlife.

Macroinvertebrates are especially useful because various kinds respond differently to stress. Some groups, such as mayflies, stoneflies and caddisflies, are generally associated with cooler, cleaner, well-oxygenated water. Other organisms, such as certain worms and midge larvae, can tolerate warmer water, lower dissolved oxygen or more disturbed conditions.

That does not mean one insect can prove a stream is healthy or unhealthy. Streams are complicated, and every site is different. But the overall community can tell a story. A single water sample gives us a snapshot of conditions at one moment in time. The living community reflects conditions over a longer period.

That is where the land becomes part of the story. A stream is tied to everything draining into it: fields, forests, pastures, roads, yards, ditches and towns. When rain falls, water moves across and through that landscape before it reaches a creek. Along the way, it can carry soil, nutrients, bacteria, leaves, grass clippings, oil, litter and plenty of other things with it.

Heavy runoff can reshape a stream in a hurry. When water moves too quickly off the land, it can scour the streambed, undercut banks and flush away the leaves, sticks, gravel and quiet pockets of water that many small animals depend on. Those changes may not be obvious from the road, but they can make a big difference to the creatures living on the bottom.

Stream wildlife reflects water quality. Water quality reflects the watershed.

Keeping soil covered, slowing runoff, protecting streamside vegetation and paying attention to what leaves a yard, road, pasture or field all help protect the small life in nearby creeks.

Healthy streams are living systems, shaped by the land around them and full of small life that often goes unseen. The small animals under the rocks may be easy to overlook, but they are part of a larger story about soil, water, habitat and stewardship.

The next time you step into a creek or pause along a stream bank, take a closer look. The smallest residents may be telling one of the biggest stories about the health of the water we all share.