Marco Invertebrate ID Sheet

Stream Assessment Manual

Stream Assessment ID Guide

Stream Assessment Form

Big Timber Creek
Macro Invertabrates and Stream Health

This important characteristic reflects the ability of the stream to support aquatic invertebrate animals. However,
successful assessment requires knowledge of the life cycles of some aquatic insects and other macroinvertebrates
and the ability to identify them. For this reason, this is an optional element. The presence of
intolerant insect species (cannot survive in polluted water) indicates healthy stream conditions. Some
kinds of macroinvertebrates, such as stoneflies, mayflies, and caddisflies, are sensitive to pollution and do
not live in polluted water; they are considered Group I. Another group of macroinvertebrates, known
as Group II or facultative macroinvertebrates, can tolerate limited pollution. This group includes damselflies,
aquatic sowbugs, and crayfish. The presence of Group III macroinvertebrates, including midges,
craneflies and leeches, suggests the water is significantly polluted. The presence of a single Group I
species in a community does not constitute good diversity and should generally not be given a score of 15.

What to look for: You can collect macroinvertebrates by picking up cobbles and other submerged
objects in the water. Look carefully for the insects; they are often well camouflaged and may appear as
part of the stone or object. Note the kinds of insects, number of species, and relative abundance of each
group of insects/macroinvertebrates. Each of the three classes of macroinvertebrates are illustrated on pages
19 and 20. Note that the scoring values for this element range from – 3 to 15. *USDA SVAP Manual

Group I
Intolerant insect species (cannot survive in polluted water)

May Fly


Caddis Fly


Caddis Fly Case


Riffle Beetle

Group II or Facultative Macro Invertebrates
Can tolerate limited pollution






Group III
Can tolerate significantly pollution.



Aquatic Worm










Pond Snail