Benthic Macroinvertebrate Index

Group I Taxa: Pollution-Sensitive Organisms

These organisms are highly sensitive to pollution. Each order of these animals which is found is given a score of 3 toward the overall index value. When they are the dominant benthic macroinvertebrates at a site, you should conclude that the water quality is good.
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[Order Coleoptera, Family Psephenidea, Genus Psephenus ]

The adult is inconspicuous and often found clinging tightly in a sucker-like fashion to the undersides of submerged rocks, where they feed on attached algae. The body is broad, slightly oval and flat, ranging from 3.5 to 6.0 mm in length. The color ranges from light brown to almost black. When flipped over, you can see the water penny's tiny legs and head.



[Order Ephemeroptera]

These insects live most of their lives in an immature state, for the mature adult life is short lived. The mayfly is a small to medium insect with delicate veined wings which are held together when at rest. At the posterior end of the abdomen there is two or three, long, segmented filaments (tails). Adult mayflies do not eat anything. They reproduce and then die. These insects are found only in the vicinity of fresh water. They may be so numerous at times that they create great hovering swarms. Newspapers have reported many times of hazardous road conditions on bridges and roads near lakes where millions of dead mayflies have left the pavement slippery enough to stop traffic. At other times, so many mayfies may land on parts of power plants that they cause massive short circuits in the power plant.

The mayfly nymph has an elongated body, stout legs and three prominent tails. Mayfly nymphs are very active dwellers in fresh water and are extremely sensitive to dissolved oxygen concentration. They cannot survive unless DO concentrations are fairly high at all times. Many species continue to be active and to grow in temperatures as low as 1-4 degrees. There are three groups common to our area: the burrowing, swimming, and the clinging mayfly.


[Order Ephemeroptera]

The burrower is the largest of the mayfly species and may reach a body length of 28 mm. Coloration varies greatly, but most are dull brown, or gray. Others are pale yellow or green. Many species have markings on the body. This type of immature mayfly burrows into bottom sediments of calmer waters and frequently leaves the burrow to feed on surface sediments. They are filter feeders and eat detritus. The nymph is characterized by the rows of gills that are often in motion, and three distinct tails.

A common burrowing mayfly of our area is Hexagenia bilineata, known as the "Canadian Soldier". Other genera of burrowing mayflies include Pentagenia, Potamanthus, Dolania, Ephemera, and Ephoron


This mayfly nymph is also known as a bottom sprawler. This type of mayfly is found crawling about on the bottom of the stream. They are stiff-legged, hairy and sometimes covered with debris. The body is depressed, and the caudal filaments are slightly fringed.


[Order Ephemeroptera]

. The clinging mayfly body is flat and small in size, ranging from 3-15 mm in length. They are found in running water, often on the underside of rocks and other objects found in the stream. The color is commonly dark, ranging from black to gray or brown. They also have the three distinct tails. They are an important source of food for trout in the riffles.



[Order Plecoptera]

There are many species of stoneflies. Several states in the United States have between 40 and 100 different species common to the area. The length of most nymphs will range from 6 to 50 mm. Body color is yellow, tan, brown or black, often a combination of two or more colors. The posterior end (rear) has two cerci (tails), which readily distinguishes them from the mayfly nymph. The stonefly nymph is sluggish and can be found in unpolluted waters within leafy/woody debris and or under stones.



[Order Megaloptera, Family Corydalidae, Genus Corydalus]

These larvae are extremely ugly and can be rather large in size, anywhere from 25 to 70 mm in length. The body is stout, elongated with spiracles (spines) and has three pairs of walking legs near the upper body and one pair of hooked legs at the rear. The head bears four segmented antennae, small compound eyes, and strong mouth parts. Coloration varies from yellowish, brown, gray and black, often mottled. Dobsonfly larvae, commonly known as hellgrammites, are customarily found along river banks under and between stones. As indicated by the mouthparts, they are predators and feed on all kinds of aquatic organisms.




[Order Trichoptera]

Several different families of caddisflies are common to our area. They have three pairs of legs near the head. The head region is darker and more durable than the soft body which is usually a delicate shade of green, tan, white or cream. Caddisfly larvae are unique in that they typically build a casing around themselves for protection from aquatic predators. The casing is made from a wide range of materials, depending on what is available: bits of leaves, twigs, grass, sand, gravel, seeds, mollusk shells and a variety of other debris. Caddisfly larvae without casings can be found in rapid running waters. Those with casings can be found in all parts of the stream. On the whole, the larvae are omnivorous (scavengers) and feed on algae, fungi, detritus, and sometimes very small invertebrates. If you happen to see a twig moving along the stream bottom or slowly creeping along the top of a submerged stone, take a closer look. It may just be a caddisfly in its house.



[Order Coleoptera, Family Elmidae, Genus Stenelmis]

Riffle beetle adults are very small insects with a body length of only 3.5 mm. Their color is commonly black. Their antennae appear segmented. They do not swim, but rather crawl along slowly. They are most commonly found in running water; hence the name Riffle Beetle.



[ Order Gastropoda ]

The vast majority of fresh water snails have a spiral shell. Eight genera of snails in the U.S. (Fresh Water Limpets) have a shell in the shape of a very low cone. Snails like waters with high calcium carbonate concentration (hard water). That is what they build their shells from. Our waters here in Northeast Ohio are rich in calcium carbonate.

Snails are "right-handed" or "left-handed." You can tell the difference by holding the shell so that its tip is upward and the opening toward you. If the opening is to the right of the axis of the shell, the snail is termed dextral -- that is it is right-handed. This types of snails are very sensitive to pollution. They need plenty of oxygen to survive. If the opening is to the left of the axis of the shell, the snail is termed sinestral -- that is it is left-handed. These are also known as pouch snails.

Right-handed snails are also known as Prosobranch, or gill-breathing snails. They possess a chalky plate called an operculum on top of their foot, which they use like a door to close the shell opening. The length or width of the shell ranges between 2 to 70 mm. The great majority of shells are black, brown, tan and gray in color. The greatest majority of Gastropods are vegetarians, eating algae, and dead and decaying plants. Most often snails can be found in waters less than 3 meters deep in more calmer parts of the stream. Several families of gilled snails are Ampulariidae, Bithyniidae, Viviparidae, Valvatidae, Pleuroceridae, Thiaridae, Hydrobiidae and Neritidae.


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