Feeding Frenzy
(Adapted from Project Wet Macroinvertebrate Mayhem Activity Copyright International Project WET, ©
International Project WET)
Overview: In this adaptation of a classic tag game, students take the roles of predators (trout) and prey
(aquatic macroinvertebrates) to model the relationships between predator and prey populations, and
the impact of water quality on aquatic creatures.
Grades: 1-3rd
Learning Objectives: Students will understand that Lake Lowell, and other bodies of water, are habitats
for a variety of animals, including macroinvertebrates. Students will learn that aquatic
macroinvertebrates are often an important source of food for fish, and that both fish and
macroinvertebrates can be affected by the quality of the water in their habitat. Students will be able to
recognize the basic requirements of good water quality (both for macroinvertebrates and for humans)—
relatively cold, clear, unpolluted water.
Vocabulary: habitat, macroinvertebrate, nymph, predators, prey, trout, mayfly, dragonfly, leech,
parasite, moult, water quality, pollution, sensitive, tolerant, moderately tolerant.
Background:
Setting up: before introducing this lesson, you will need to set up two “baselines,” or boundaries, 50100 feet apart. You will also need the laminated macroinvertebrate visuals, and nametags (enough for
all the students) with the three different types of macroinvertebrates (mayflies, dragonflies and leeches)
and 5-10 trout nametags.
Introducing the game:
Today we’re going to learn about an animal that lives in Lake Lowell. Lake Lowell is a habitat for lots of
different kinds of animals—it is where they live, and it provides the things they need to survive (What do
all living things need to survive? Food, water, shelter, space). What are some kinds of animals that live
in the lake, or near the lake? (Fish, birds, deer…). The animal that we are going to talk about today is a
very tiny animal called a macroinvertebrate. Macroinvertebrate is a long word for an animal that is very
small, but big enough for you to see without a microscope or magnifying glass. Macroinvertebrates
don’t have skeletons made of bones on the insides of their bodies like we do. Can you think of some
examples of animals that don’t have bones? Some examples are worms, spiders, snails, shrimp, oysters;
and insects like flies and other bugs. The macroinvertebrates that we’re going to learn about are
aquatic macroinvertebrates, meaning that they spend all or part of their lives in the water. Some
examples are things like leeches, and also immature mayflies and dragonflies (the immature life cycle
states of these insects are called nymphs).
Now, what do you think that the little macroinvertebrates that live in Lake Lowell would eat? Many of
them help to “clean up” the water, by eating algae, plants and rotting things. Some macroinvertebrates
even eat other macroinvertebrates! What do you think lives in Lake Lowell that would eat the
macroinvertebrates? Lots of fish, like trout and bass, use macroinvertebrates as food, and so do many
birds, like ducks.
Playing the game—round 1:
Tell the students that they are going to play a game, called Feeding Frenzy, that helps illustrate the
relationship between fish and aquatic macroinvertebrates. Ask someone to remind everyone what a
macroinvertebrate is. What is one kind of aquatic macroinvertebrate that could live in Lake Lowell?
(Dragonfly nymph, mayfly nymph, leeches would all be good answers). Ask everyone if they know the
difference between predators and prey. (Predators are the hunters; prey are what gets eaten). In this
game, a trout is the predator, and the macroinvertebrates are the prey.
Have the entire group line up along one of the baselines. Pick one to three volunteers to be a trout (give
them trout nametags), and have them stand in the middle of the playing field, between the two
baselines. You should have more trout if it is a larger group, and fewer if it is a small group. Everyone
else is a macroinvertebrate. Explain the rules:
When you say, “go,” all of the macroinvertebrates have to run across the playing field, trying to make it
to the opposite baseline without being tagged by the trout. Once you get across the baseline, you are
safe. If you get tagged by a trout, you have been eaten. Trout should gently tag, not shove or hit, the
other players. Macroinvertebrates that get eaten should stand or sit behind one of the baselines and
wait for the end of the game. The game ends when all the macroinvertebrates have been eaten.
At the end of the game, have everyone, including the trout, line back up on a baseline. Pick new trout,
but this time, add 2-3 additional trout to your original number. Play until all the macroinvertebrates
have been eaten. At the end, ask students how increasing the number of predators (trout) changed the
game. Ask them to apply this to Lake Lowell—how could changing numbers of predators (fish and birds)
in the lake affect the numbers of macroinvertebrates in the lake? What might happen to the
macroinvertebrates if there were more predators? What if there were fewer predators in the lake?
Playing the game—round 2:
Now, as we learned earlier, there are many different types of macroinvertebrates. Before we play
again, we’re going to learn a bit more about of couple of the different kinds of macroinvertebrates that
could live in Lake Lowell.
The first one is a mayfly nymph—the immature version of mayflies. They look like this:
Mayfly nymphs are immature mayflies, and live in water. Nymphs can live in their aquatic home for a
few months or even a few years. They mostly eat algae and rotting bits of plants that are found in the
water. When they are ready, the nymph swims up to the surface of the water and moults into an adult
mayfly with wings. The adult version sheds the shell that used to be the nymph, and flies off. The adults
only live for a few days at most. Adult mayflies don’t eat at all, but before she dies, a single female
mayfly can lay 3000 eggs on the water. These eggs will eventually become mayfly nymphs. The eggs
look like this—a dark, gooey mess:
However, if you look at them with a microscope, they look like this. In this photo, you can actually see
some of the baby mayflies (that will become nymphs) hatching out of their eggs.
The second is a dragonfly nymph. What does “nymph” mean? It’s the immature version of adult
dragonflies. They look like this:
Dragonfly nymphs are the immature version, and live in water. They hunt other aquatic
macroinvertebrates, and even tadpoles and small fish! They can live as nymphs for several years, and
then eventually the nymph will climb up out of the water on a tall reed or piece of grass, and will
transform into an adult dragonfly. The adult dragonfly actually climbs right out of the empty “shell” that
used to be the nymph. Adult dragonflies only live for a couple of weeks. They snatch their prey out of
the air. This dragonfly is eating a mosquito that it has caught. Before they die, adult dragonflies lay
their eggs on the water. What do you think these eggs will become? That’s right, dragonfly nymphs!
The last one is a leech.
Leeches are a kind of worm. Many of them are aquatic, and unlike the other two macroinvertebrates
we have discussed, many leeches spend their whole lives in the water. Some leeches are parasitic—
they latch onto humans and other big animals, and feed on their blood. Most leeches, however, actually
just feed on other macroinvertebrates—not blood!
In medieval times, parasitic leeches were used by doctors as a medicinal treatment, to remove blood
from patients who were ill. This was called “bloodletting.” It is not something that doctors think is a
good idea anymore, for most illnesses. However, leeches are still used occasionally in some specific
types of surgeries, because they can latch onto a vein and keep the blood from clotting.
Each of these types of macroinvertebrates (mayfly nymphs, dragonfly nymphs, and leeches) have
different needs when it comes to the kind of water they live in. Most people prefer the water they drink
to be clear, cold and not polluted. Mayflies are like humans in this way—they need high water quality
(cold, clear and unpolluted) to survive. If the water becomes too warm, murky, or polluted, the mayfly
nymphs aren’t able to breathe (they are like fish, they breathe oxygen underwater through gills on their
sides). Because of this, mayflies are called “sensitive” to pollution.
Leeches are the opposite: they can survive easily in places with low water quality. What does low
water quality mean? Places with low water quality have water that is warmer and often murky, muddy,
or clouded—you can’t see through it. Low water quality can also mean that the water has been
polluted. Leeches are tolerant of pollution and low water quality, which means that they can survive
well in places where mayfly nymphs would die. Leeches can live in places with high water quality, too.
Leeches can live in almost any kind of water.
Dragonfly nymphs are in the middle. They are called “moderately sensitive” because they aren’t as
sensitive as the mayflies and they also aren’t as tolerant as the leeches. They can survive well in places
with high water quality and they do okay if the water quality gets a little worse…but if it gets too bad,
they can’t survive.
This round, play the game as before (with new trout volunteers), but hand out macroinvertebrate
nametags (dragonfly, leech, mayfly) to all the students in roughly equal amounts. Before you start, ask
all the mayflies to raise their hands, then all the dragonflies, then leeches, so that they can get a sense of
the proportions. Review sensitivity/tolerance of each type of macroinvertebrate. Before you start, give
a little habitat information—for this game we’re going to start out in an area with very high water
quality. What does that mean? Very cool, clear water! We might be in a mountain stream or clear
mountain lake. Which of our three types of macroinvertebrates (mayflies, dragonflies, leeches) will do
well in this environment? All of them. Because we are in a habitat with high water quality, all of our
macroinvertebrates are doing just fine. Have them all run to the opposite baseline normally, trying not
to get tagged, when you say “go.” When they reach the opposite baseline, have them raise their hands
by macroinvertebrate group again, so everyone can see who is left. Have anyone who was tagged out
stand aside. (Hopefully, it will still be roughly equal among the three groups.
Now, before they get to run back across, you’re going to change the habitat a bit, so that they can
visualize the impact of water quality on survival. Tell them that now we are in an area with a little lower
water quality—it is warmer water and slightly murkier. The water is kind of cloudy and harder to see
through. Maybe there was a flood recently and the river swept a lot of leaves and soil into their lake.
Which macroinvertebrate is going to be hit hardest by the decrease in water quality? Mayflies, because
they are a sensitive species. The leeches are doing fine, and the moderately sensitive dragonflies are
still doing okay, but the mayflies are starting to have a hard time breathing. So to demonstrate, for the
next run, the dragonflies and leeches and trout can still run normally, but the mayflies have to hop on
one foot all the way across. Stop them all again when they reach the other baseline, and raise hands by
groups again. This time, there should be much fewer mayflies left. Does this make sense? Yes, because
the mayflies only survive well in habitats with high water quality. Next, we are in an area with very low
water quality. It’s really warm and muddy, there’s a lot of trash in it, it smells bad…now the mayflies
really can’t breathe at all and even the dragonflies are starting to have a hard time. Mayflies now have
to hop with two feet while flapping their arms like gills. Dragonflies have to hop on one foot all the way
across. Leeches are still fine though, so they are allowed to run.
Continue to play until everyone is out, but keep stopping between rounds to count how many of each
type of macroinvertebrate is left, and to discuss this. If time allows, you can play again, reassigning
students to different macroinvertebrates and trout so they have a chance to play a different role. As
much as possible, find opportunities to select new trout, since that tends to be a popular role. You can
add many more variations to this game—more different habitat types and challenges for the affected
macroinvertebrates. You can also play again, but point out that trout are also impacted by habitat (like
mayflies, they need high water quality), so you can give challenges to the trout that make it increasingly
difficult for them to catch their prey, just as the sensitive and moderately sensitive prey species have an
increasingly hard time getting away as the water quality gets worse.
Leave a couple minutes at the end of the program to recap the main points with the students and allow
for questions.