Using Dichotomous Keys

Introduction A dichotomous key is a tool that allows the user to determine the identity of items in the natural world, such as trees, wildflowers, mammals, reptiles, rocks, and fish. "Dichotomous" means "divided into two parts". Therefore, dichotomous keys always give two choices in each step.

Hints: Focus on 1 organism at a time Use constant characteristics rather than variable ones. (Flowers change with the seasons) Use measurements rather than terms like "large" and "small". Make the choice a positive one - something "is" instead of "is not". If possible, start both choices of a pair with the same word. Finish the dichotomous key with a description of the organism

1. a. wings covered by an exoskeleton – go to step 2 b 1. a. wings covered by an exoskeleton – go to step 2 b. wings freely observed – Go to step 3 2. a. body has a round shape ……….ladybug a red beetle with black spots b. body has an elongated shape ……….grasshopper a green insect that hops 3. a. wings point out from the side of the body ……….dragonfly an insect that is 10- 15 cm long and lives in marshes b. wings point to the posterior of the body ……….housefly a flying insect with red eyes and an annoying buzz

Macroinvertebrates Sampling

Why Study the Stream-Bottom Macroinvertebrates? They are an important part of the community of life found in and around a stream. They differ in their sensitivity to water pollution. They provide information about the quality of a stream over long periods of time. Stream-bottom macroinvertebrates are relatively easy to collect.

Macroinvertebrates That Are Sensitive to Pollution Found in Good Quality Water

Macroinvertebrates That Are Somewhat Sensitive to Pollution Found in Good or Fair Quality Water

Macroinvertebrates That Are Tolerant of Pollution Found in Any Quality Water

Using this data ID the macroinvertebrates and figure out if the steam is Good, Fair or Poor water quality.

GOOD WATER!

Sample Collection Procedures 1. Selecting a site – Find a riffle that is typical of the stream. A good riffle for sampling will have cobble-sized stones, fast-moving water, and a depth of 3 to 12 inches. Select a 3-foot by 3-foot area within the riffle for sampling.

2. Positioning the kick seine Have one person hold the net upright facing the flow at the downstream edge of the sampling area. The net should be stretched out to its full 3-foot width with the bottom edge lying firmly against the stream bed. No water should wash under or over the net. If needed, small rocks can be used to weigh down the bottom edge of the net. NOTE: Don’t walk through your sampling area! You may disturb the insects

3. Collecting the sample All macroinvertebrates in the 3-foot by 3-foot sample area are to be washed into the kick seine. For at least sixty seconds, kick the stream bed with a sideways shuffling motion towards the net. The object is to thoroughly work up the stream bed to a depth of several inches. You WANT small gravel to be caught in your net

4. Removing the kick seine from the water When Step 3 is completed, lift the kick seine out of the water with a forward scooping motion. The object is to avoid losing any macroinvertebrate specimens while the seine is lifted. The easiest way to do this is by having all 3 team members work together to lift the seine.

5. Removing the sample from the kick seine Carry the kick seine to the stream bank and spread it out flat. Carefully examine the net and the collected debris for macroinvertebrates. Look carefully as many specimens will be small and hard to see. Using tweezers or fingers, place all the specimens in ice trays. Sort them into different types as you remove them from the net. Using a dichotomous key, identify the different insects found in your sample.