Insects as Bioindicators of Stream Health
Insect Ecology Experiential Day: October 16, 2013
Objectives: Identify aquatic macroinvertebrates, calculate their diversity using the Shannon
Diversity Index, and learn how they can be used as bioindicators of stream health.
Materials:
D-frame nets
white pans
forceps
light microscopes
vials
tape
calculator
markers
Note:
You will be “stream stomping” – you will get wet, so wear appropriate shoes and
pants.
Overview: You will collect macroinvertebrates (insect larvae and other aquatics) at two
different streams. Back at the laboratory, you will identify the major groups of
macroinvertebrates and use the information to “grade” the stream health using a
diversity index.
Sampling Procedure:
1) Divide into teams of two. Each team needs a D-frame net, forceps, vials and a white pan.
2) Enter the stream. One of you shuffles your feet in the sediment for 1 minute to kick up
invertebrates while the other stands downstream and holds the D-frame net tight against
the stream bed to catch the invertebrates.
3) Bring the net to the shore and pour the contents into a white pan filled with stream water.
4) Use the forceps to carefully pick out invertebrates and put them in vials with water. Label
the vials with the stream name and location.
5) Do the stream collection technique two times at each stream location. Take turns kicking
up the sediment and holding the net.
6) Make and record observations regarding stream depth, flow, and habitat at each location.
Student Name: ___________________________________ Lab Partner: __________________
Insects as Bioindicators of Stream Health: Assignment
Before Class: Answer the following questions before coming to class.
1) What is a macroinvertebrate?
2) Why might macroinvertebrates be good bioindicators of stream health?
3) What factors might influence macroinvertebrate diversity within a stream?
During Class: Work with your lab partner to answer the following questions:
1) What two streams did you sample today?
2) Compare and contrast observations at the two different stream habitats. What was the
surrounding area like at each stream? How deep was the water? Did the water have the same
flow rate?
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3) Fill in the tables with the results of your collection. Refer to the Macroinvertebrate
Identification Guide for help.
Group
Macroinvertebrate Type
1
Ephemeroptera (mayflies)
2
3
4
5
6
Plecoptera (stoneflies)
Trichoptera (caddisflies)
Coleoptera (beetles)
Odonata (dragonflies, damselflies)
Megaloptera (dobsonflies)
7
8
9
10
11
12
Crustaceans (scuds)
Diptera (true flies)
Aquatic worms
Hemiptera (true bugs)
Mollusks
Isopods
Stream 1
Round 1
Stream 1
Round 2
Total
Stream 2
Round 1
Stream 2
Round 2
Total
TOTAL (add number in each column)
Group
Macroinvertebrate Type
1
Ephemeroptera (mayflies)
2
3
4
5
6
7
Plecoptera (stoneflies)
Trichoptera (caddisflies)
Coleoptera (beetles)
Odonata (dragonflies, damselflies)
Megaloptera (dobsonflies)
Crustaceans (scuds)
8
9
10
11
12
Diptera (true flies)
Aquatic worms
Hemiptera (true bugs)
Mollusks
Isopods
TOTAL (add number in each column)
2
Communities vary in the number of species they contain. Knowledge of this number is
important to understand the structure of the community. The number of species in a community
is referred to as species richness. The relative abundance of species is also important. For
example, two communities may both contain the same number of species but one community
may be dominated by one species while the other community may contain large numbers of all
species. The relative abundance of species is called evenness. Communities dominated by one or
a few species have a low evenness while those that have a more even distribution of species have
a high evenness. Species diversity includes both species richness and evenness.
4) Describe how species richness and evenness are different.
5) Describe the species richness and evenness for each stream.
6) Identify which stream you expect to be the most diverse and defend your choice.
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Next you will learn how to measure the macroinvertebrate diversity for each stream using
Shannon’s Diversity Index. It is calculated using this equation:
H’ = – ∑ pi (ln(pi))
Example Dataset:
Calculate Shannon’s Diversity Index for
the following tree species.
First add the number of all
individuals (here the total is 62).
Next calculate pi, or the proportion of
each species. This is done by taking the
number of individuals of each species
and dividing it by the total number of
individuals.
where pi = the proportion of individuals of species i
Species
Beech
Maple
Oak
Total
Species
Beech
Maple
Oak
Total
Number of
Individuals
32
18
12
Number of
Individuals
32
18
12
62
pi
ln(pi)
pi
ln(pi)
(32 / 62) = 0.52
(18 / 62) = 0.29
(12 / 62) = 0.19
-0.65
-1.24
-1.66
Now calculate the natural log of pi.
Now calculate the diversity using the equation:
H’ = – ∑ pi (ln(pi))
H’ = – [(0.52 x -0.65) + (0.29 x -1.24) + (0.19 x -1.66)]
H’ = – [(-0.338) + (-0.360) + (-0.315)]
H’ = – (-1.01)
H’ = 1.01

When given a large sample size (e.g. more than 5 species), the Shannon
Diversity Index values (H’) can range of 0 to ~4.6 using the natural log
(ln). A value near 0 would indicate that every species in the sample is the
same. A value near 4.6 would indicate that the number of individuals is
evenly distributed between all the species.
4
7) Calculate the Shannon Diversity Index for Stream 1. Fill in the table below to solve for pi and
ln(pi), and then use the extra space to calculate H’.
Stream 1
Macroinvertebrate Type
Total Collected
in Stream 1
pi
ln(pi)
Ephemeroptera (mayflies)
Plecoptera (stoneflies)
Trichoptera (caddisflies)
Coleoptera (beetles)
Odonata (dragonflies, damselflies)
Megaloptera (dobsonflies)
Crustaceans (scuds)
Diptera (true flies)
Aquatic worms
Hemiptera (true bugs)
Mollusks
Isopods
TOTAL
Use the values you calculated in the table above to solve for H’ (Shannon Diversity Index value):
H’ = – ∑ pi (ln(pi))
H’ =
5
8) Calculate the Shannon Diversity Index for Stream 2. Fill in the table below to solve for pi and
ln(pi), and then use the extra space to calculate H’.
Stream 2
Macroinvertebrate Type
Total Collected
in Stream 2
pi
ln(pi)
Ephemeroptera (mayflies)
Plecoptera (stoneflies)
Trichoptera (caddisflies)
Coleoptera (beetles)
Odonata (dragonflies, damselflies)
Megaloptera (dobsonflies)
Crustaceans (scuds)
Diptera (true flies)
Aquatic worms
Hemiptera (true bugs)
Mollusks
Isopods
TOTAL
Use the values you calculated in the table above to solve for H’ (Shannon Diversity Index value):
H’ = – ∑ pi (ln(pi))
H’ =
6
9) What Shannon Diversity Index value did you calculate for Stream 1? Stream 2?
10) Identify the stream that was the most diverse. Based on your observations during the lab,
explain why your prediction in question #6 was supported or not supported.
11) The importance of biodiversity has been correlated to ecosystem resilience and stability.
According to your results, which stream demonstrates the higher degree of ecological
stability? Why?
12) List and elaborate on any potential sources of error that may have affected your results.
13) Do you think it is important to survey streams for macroinvertebrates? Why? What can this
information tell us?
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Macroinvertebrates have different levels of tolerance to stream pollution. For example:
Groups 1 – 4 (mayflies, stoneflies, caddisflies and beetles) are all highly sensitive to
pollution. They require higher levels of dissolved oxygen in the water to survive, a
neutral pH, and cold water temperatures.
Groups 5 – 7 (dragonflies, damselflies, dobsonflies and scuds) are moderately sensitive
to pollution.
Groups 8 and 9 (midge larvae and aquatic worms) are very tolerant to pollution. They
can tolerate low amounts of dissolved oxygen in the water, acidic and alkaline pH, and
warmer water temperatures.
Groups 10 – 12 (true bugs, mollusks and isopods) vary in their sensitivity to water
quality.
14) What types of macroinvertebrates would you expect to find in a healthy stream? In a
polluted stream?
15) List the three most abundant macroinvertebrates you collected from each stream.
Stream 1:
Stream 2:
16) What does this information tell you about the health of these streams? Are they healthy or
unhealthy? How do you know?
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Macroinvertebrate Identification Guide
Ephemeroptera (mayflies)
Adult
Nymphs – gills on abdominal segments, usually 3“bristles”
Plecoptera (stoneflies)
Adult
Nymphs – 2 tarsal claws, 2 long filamentous tails
Trichoptera (caddisflies)
Adult
Nymphs and cases
1
Macroinvertebrate Identification Guide
Coleoptera (beetles)
Nymphs – chewing mouthparts, 3 pairs of legs
Adult
Odonata (dragonflies, damselflies)
Nymphs – large eyes, 3 pairs of legs; Dragonflies have a stout
body (no tails); Damselflies have a slender body and 3 tails
Adults
Megaloptera (dobsonflies)
Adults
Nymphs
2
Macroinvertebrate Identification Guide
Crustaceans (scuds)
Adult
Nymphs
Diptera (true flies)
Adult
Nymphs
Aquatic worms
Adults
3
Macroinvertebrate Identification Guide
Hemiptera (true bugs)
Adults – piercing/sucking mouthparts
Mollusks
Adults
Isopods
Adults
4