Benthic Macroinvertebrate Index

Group 4 Taxa: Other Invertebrates


These organisms are not included in the Ohio Department of Natural Resources' Benthic Macroinvertebrate Index. However, you are likely to see them in most streams in Ohio. Most are most noticeable -- and not included in the ODNR index for precisely the same reason -- they are not benthic organisms. They are swimmers or walkers. They may or may not be an indicator of water quality. But you should take note of them anyway, because they include some interesting organisms.
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WATER SCORPION

[ Family Nepidae, Genus Ranatra ]

They are called water scorpions because the forelegs resemble the pedipalps of scorpions. The general body shape varies greatly, however, all species have two long, slender, nonretractable caudal (rear) filaments which they use for breathing purposes. They are inconspicuous because of their protective coloring and sluggish movements. They can be found in trash and mud of shallows and in grassy areas of the stream. They feed on aquatic Metazoa and insects by sucking out the body fluids. They are capable of flight and make a clicking noise while doing so. Some insect books downplay their ability to fly, but personnel associated with this project have seen them fly, and can assure you that they can fly quite fast!

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GIANT WATER BUG

[Family Belostomatidae, Genus Belostoma]

The Giant Water Bug is the largest of the Hemiptera, or true bugs, in Ohio. Their body length ranges from 20 to 70 mm. The body is flat and oval shaped, with color ranging from brown to dullish green. The forelegs are raptorial for grabbing prey while the hind legs are ciliated for swimming. Found on the bottom of shallow quiet waters or clinging to vegetation. They are fiercely predaceous and feed on aquatic organisms such as tadpoles, small frogs and fishes. Even people should use caution while collecting, since their bite can cause a painful swelling.



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WATER BOATMAN

[Order Hemiptera, Family Corixidae, Genus Corixa]

The Water Boatman is the most common of all aquatic insects. They take their name from their appearance, their hind legs are long, flattened and fringed for swimming which are used in an oar-like fashion. The body is usually less than 12 mm and the color is customarily dark grayish and often mottled with yellow, brown or black. They are bottom feeders and eat protozoa, microscopic metazoa, and algal filaments. Most species are strong fliers and take off easily from the water surface. These creatures are fast, erratic swimmers which are found above and below the water surface.



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BACK SWIMMER

[Family Notonectidae, Genus Notonecta]

Backswimmers are by far the most common members of the family Notonectidae. They look somewhat like water boatmen, and they are approximately the same size and shape. However, these bugs are easily distinguished because they swim primarily on their backs and have unusually large eyes. They are also capable of flight. The color is black and white but may range from pearly, yellow, gold, tan and brown. If handled carelessly they "sting" sharply and produce a burning sensation. Mature forms feed on insects and even small tadpoles and small fishes.



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WATER STRIDER

[Family Gerridae, Genus Gerris ]

The Water Strider is semi-aquatic and can be found from early spring until late autumn. Body length is 1.6 to 5.5 mm, and the color is brown or black. They have long legs and can be found skating along the surface of the water by utilizing waters tension. When disturbed they scatter around in all directions. They feed on insects on the surface and just below the surface of the water. If food is scarce, they may become cannibalistic and feed on members of their own species.



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