UNIT 01
CAPTIVATING CREATURES
FROM MICROSCOPIC PLANKTON TO THE GIANT WHALES THAT DEVOUR THEM, THE DIVERSITY OF CREATURES ON EARTH IS ASTONISHING, AND THERE ARE FASCINATING LIVING THINGS EVERYWHERE YOU LOOK.
While some organisms such as algae simply double their DNA and divide, others have developed more complicated ways to reproduce. Animals that undergo metamorphosis experience dramatic developmental changes, allowing them to transition from one habitat to another. While tadpoles move from water to land, caterpillars transform, unfurl their wings, and take to the air as butterflies.
Tiny tardigrades, nicknamed water bears for their bearlike claws, don’t undergo metamorphosis but are extreme survivalists that can dehydrate themselves to withstand extreme heat, cold, radiation, and even outer space.
Every scoopful of sand or muck from a pond or stream is teeming with an enormous variety of life. From ferocious dragonfly larvae to pinching crawfish, you’ll be amazed at what’s hiding under the pebbles and twigs.
Carefully capturing and observing living things is a great way to glean insight into the fascinating creatures sharing our world. As you do the labs in this unit, keep in mind that every living animal houses an entire microbial community of its own, so it is essential to release each organism where it was captured to avoid spreading disease from one population to another.
LAB 01
MACROINVERTEBRATE MARVELS
USE KITCHEN STRAINERS TO COLLECT, SORT, AND IDENTIFY FRESHWATER INVERTEBRATES FROM A LAKE, POND, OR STREAM.
MATERIALS
Very fine mesh kitchen sieves or mesh screen food cover
White bowls or trays
Strainer with larger mesh, or piece of screen (optional)
Plastic spoons, forceps, or tweezers for picking up invertebrates
Bowl or bucket
Empty ice cube tray
Magnifying glass
Identification key
SAFTEY TIPS & HINTS
— Never leave small children unattended near water.
— Assist small children in collecting invertebrates.
— Find a shallow spot where it’s easy to wade in at the water’s edge.
PROTOCOL
STEP 1: Scoop up sand and mud from the water’s edge using a kitchen sieve with very fine mesh. (Fig. 1, 2)
Fig. 1: Scoop up some muck.
STEP 2: If you don’t have a second screen or colander, dump your sample into a white bowl or onto a white tray and watch for movement. (Fig. 3)
Fig. 3: Dump your sample into a white bowl.
STEP 3: If you have a screen or strainer with larger holes, prop it up over the white bowl or tray and dump the muck onto the larger mesh. Wait about 10 minutes. Some invertebrates will drop through the screen on their own onto the surface below. Dump the remaining muck into a second white container.
STEP 4: Gently collect invertebrates from your samples using spoons, forceps, tweezers, or your fingers. Place larger invertebrates, such as snails, clams, or crayfish, in a bowl or bucket with some lake, pond, or stream water. Smaller invertebrates may be sorted into ice cube trays.
STEP 5: Observe the invertebrates with a magnifying glass. Record how many legs each has, and where they are located. Draw them in your science notebook. Record how the invertebrates move around and any unusual features. (Fig. 4)
Fig. 4: Observe invertebrates with a magnifying glass.
STEP 6: Use a macroinvertebrate identification key, like the one you can download at stroudcenter.org, to attempt to identify some of the creatures you’ve captured.
STEP 7: Release the invertebrates in the same spot where you captured them.
CREATIVE ENRICHMENT
1. Do you live near the ocean? Try doing a macroinvertebrate study in the sand by the surf.
2. Capture macroinvertebrates using a net in a stream or other running water. Do you see the same creatures you find in the mud at the water’s edge?
3. Dig up some dirt and sift it through a screen. What soil macroinvertebrates do you find?
LAB 02
WATER BEAR HUNT
SEARCH FOR TINY TARDIGRADES LURKING IN MOSS AND LICHENS.
MATERIALS
Lichens and moss, gently scraped from trees
Bottled water
Petri dish
Microscope
SAFTEY TIPS & HINTS
— Collect plenty of lichens and moss.
— Young children will need help finding the tardigrades but will love observing them through the microscope.
— Don’t get frustrated if you don’t find a tardigrade on your first attempt. If you keep looking, you will find one!
PROTOCOL
STEP 1: Go on a walk and search for moss and lichens on trees. Moss is often green and velvety, while lichens look more like blue-green or blue-gray crinkled crust growing on tree bark. Gently scrape moss and lichens into a container and bring them home. (Fig. 1)
Fig. 1: Search for lichens, like the ones in this photograph, and moss growing on tree bark.
STEP 2: If the moss and lichens are dry, partially cover them with bottled water and let them sit overnight. If they’re damp and soft, partially cover them with bottled water and soak them for 5 or 10 minutes. (Fig. 2)
Fig. 2: Soak the moss in bottled water.
STEP 3: When you’re ready to look for tardigrades, gently remove the moss and lichens from the water and shake them over a petri dish, collecting the drops of water in the dish. Squeeze excess water from the moss into the petri dish to form a shallow layer of water. (Fig. 3)
Fig. 3: Shake and squeeze water from the moss into a petri dish.
STEP 4: Observe your water sample with a microscope, using the lowest power. It may help to wait a few minutes for everything to settle to the bottom of the petri dish. Look for things that move and are somewhat transparent and pink. (Fig. 4)
Fig. 4: Search for tardigrades using a microscope.
STEP 5: You can distinguish tardigrades from other living organisms by their four pairs of legs. They look a bit like caterpillars or strange pigs. (Fig. 5)
Fig. 5: Tardigrades look a bit like caterpillars or strange pigs.
STEP 6: Once you find a tardigrade, center it in the field of vision and increase the magnification for a closer look.
STEP 7: Try to take a picture or video of the tardigrade or draw it in your science journal. See Resources for a link to a video we made of one of the tardigrades we found.
CREATIVE ENRICHMENT
Collect moss and lichens from the ground and trees. Where do you think you’ll find more tardigrades? Test your hypothesis, using your science journal to record your results.
LAB 03
TADPOLE TRANSFORMATION
WATCH TADPOLES SHAPE-SHIFT INTO FROGS AND TOADS.
MATERIALS
Water containers, such as jars
Fish net or bucket for catching tadpoles
Larger container to use as habitat
Green lettuce boiled for 5 minutes in bottled water and finely chopped (tadpole food)
SAFTEY TIPS & HINTS
— Never leave young children unattended near water.
— Never use tap water for your tadpole habitat because chlorine can kill tadpoles.
— Always follow local regulations regarding natural resources and release frogs and toads in exactly the same place you captured the tadpoles to prevent the spread of disease and nonnative species. Never capture tadpoles unless you can return them to the same spot where you caught them!
PROTOCOL
STEP 1: Check regulations for capturing tadpoles in your area. See whether you can spot some tadpoles in a puddle, fountain, lake, or pond. If local regulations prevent you from catching them, you can keep checking tadpoles to watch them develop in their natural habitat.
STEP 2: If you see tadpoles in the water, collect some of the water in your container. Gently net a few tadpoles and carefully place them in the container. Collect more water and some algae for future use to keep your habitat healthy for the tadpoles. (Fig. 1, 2)
Fig. 1: Gently net a few tadpoles.
STEP 3: Find a large container with a cover or make a cover from a screen. Make sure there are air holes so the tadpoles can breathe. Create a tadpole habitat using the water and algae you collected, including raised areas like rocks for frogs or toads to hop onto when they’re mature. (Fig. 3)
Fig. 3: Create a habitat for the tadpoles.
STEP 4: Place the tadpoles in the habitat and observe them every day, adding more water as needed. Make sure some raised, dry areas remain in the habitat.
STEP 5: Every other day or so, feed the tadpoles some tadpole food made from boiled lettuce.
STEP 6: Draw your tadpoles every few days in a notebook. Eventually you’ll see legs grow and the tails disappear as they move through metamorphosis.
STEP 7: When your tadpoles hop out of the water, return them to the place where you caught them, so they can find food. (Fig. 4, 5)
Fig. 4: Return the frogs or toads to the place where you caught the tadpoles.
CREATIVE ENRICHMENT
Keep a metamorphosis journal detailing when the tadpoles are most and least active and how many days it takes for them to form back legs and front legs and to lose their tails. Do they all develop at the same rate?
LAB 04
BUTTERFLY GARDEN
OBSERVE THE MIRACULOUS TRANSFORMATION FROM CATERPILLAR TO BUTTERFLY.
MATERIALS
Local plants that butterflies are known to lay eggs on, such as milkweed and dill in North America
Cup or vase partially filled with water
Foil or plastic wrap
Large covered container
More butterfly-friendly plants or seeds for local plants to put in your garden (optional)
SAFTEY TIPS & HINTS
— The best way to pick up a butterfly is by gently pinching its closed wings between your thumb and index finger.
— If you absolutely must move the chrysalis from its perch, firmly wrap and tie a piece of thread around the tiny stem at the top, carefully remove it, and hang it in a safe spot. Be extremely careful not to drop it.
PROTOCOL
STEP 1: Research which plants butterflies are known to lay eggs on in your area and look for pictures of butterfly eggs. Search the undersides of leaves for butterfly eggs and caterpillars. Butterfly eggs are very tiny, about the size of a pinhead, and are usually lightly colored. (Fig. 1)
Fig. 1: Search for eggs and caterpillars.
STEP 2: If you find an egg or caterpillar, leave it on the leaf and take the entire stalk of the plant home. Collect more stalks and leaves of the same kind to feed your caterpillar. (Fig. 2)
Fig. 2: If you find an egg or caterpillar, take the entire plant stalk home and put it in water.
STEP 3: Put the stem of the plant in a cup or vase containing some water, with foil or plastic wrapped tightly around the bottom of the plant and vase so the caterpillar won’t fall in and drown. Place the plant in a larger container with a cover, such as a piece of screen.
STEP 4: Watch the egg hatch and the caterpillar grow. Replace the plant if it dies or all the leaves are eaten. (Fig. 3)
Fig. 3: Watch the caterpillar grow.
STEP 5: Check the caterpillar every day until it hangs upside down and turns into a chrysalis. As long as you give it fresh leaves, it will get all the water and nutrients it needs from the plant. (Fig. 4)
Fig. 4: The caterpillar will turn into a chrysalis.
STEP 6: When the butterfly emerges, leave it alone for at least one day. It has to hang upside down to pump fluid into its new wings. (Fig. 5)
Fig. 5: Let the newly emerged butterfly hang upside down.
STEP 7: Release the butterfly.
STEP 8: Plant butterfly-friendly flora in your yard to find more caterpillars next year. You may even help a species survive by providing a place for them to lay their eggs. (Fig. 6)
Fig. 6: Plant butterfly-friendly plants in your garden.
CREATIVE ENRICHMENT
Keep a journal of your caterpillar’s growth and development. Measure it every day and record how long it takes to emerge from the chrysalis.