Animal Two by Two
Plant and Animal Care

Students investigate the following animals in the Animals Two by Two Module

Goldfish and Guppies
Land Snails
Aquatic Snails
Red Worms and Nightcrawlers
Pill Bugs and Sow Bugs

Click on any animal to find out specific information about its care.

Introduction to Life in the Classroom

In several of the FOSS modules and courses, living organisms are brought into the classroom to be cared for and observed by K-5 students. Through the direct experience with organisms provided by these modules, we hope to engender in students a sense of respect for all life and to spark a desire to understand the complex systems that support life on Earth.

The FOSS program endorses the National Science Teachers Association Guidelines for Responsible Use of Animals in the Classroom as they apply to elementary and middle school classrooms.

The FOSS program provides detailed information on how to obtain organisms, how to prepare for their arrival, how to care for them in the classroom, and how to instruct students to properly handle each animal. The animals in the modules were selected because they are abundant, safe for students, easy to care for, and hardy and well-adapted to classroom environments. FOSS selected organisms that were nonexotic, commonly available from local and regional suppliers, and, in some cases, found in the natural environments in many regions. When investigations are carried out as described in the FOSS teacher guide, the insects, worms, crustaceans, snails, and fish are not harmed in any way.

To read more about the FOSS/Delta Policy Statement on Living Organisms in the Classroom, please click here.


Plants occupy the base of the food pyramid in aquatic systems just as they do in terrestrial systems. Inconspicuous single-celled algae that turn your aquarium green capture the sun's energy and provide food for countless minute animals in the water. If you want to stimulate an algae bloom (population explosion), put a goldfish in an aquarium, place it where it will get direct sun several hours a day, and provide the fish with plenty of food. When you see the water turn green, it's a sign that your aquatic plants are growing beautifully.

FOSS activities also use vascular aquatic plants. The popular goldfish-bowl plant that looks like a green feather boa is Elodea (or sometimes Anacharis). In nature it is usually rooted to the bottom of a stream or pond, but in your aquarium it can just float around. It is a good food source for amphipods, fish, and crayfish and will contribute to the oxygen in the water as it photosynthesizes. It also provides crannies where small animals can hide from predators.

Care of aquatic plants is easy. Keep plenty of water in their container.

What to do when the plants arrive. Open bag and rinse plants in dechlorinated or spring water. Keep Elodea floating in bowl of dechlorinated or spring water to avoid drying out until it's ready to use.

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Plants and animals that live in water make up the majority of biomass. They have so much more space in which to live. Life undoubtedly originated in the water, and many life-forms have never left it. Living in a dense fluid like water provides a lot of support for organisms, and the free-swimming forms have three-dimensional mobility. And, of course, they never have to worry about where their next drink is coming from.

For many of us a goldfish bowl was our introduction to aquatic animals. The beautiful orange fish are hardy and forgiving in terms of their living requirements. They are good classroom animals, requiring a minimum amount of care to keep them in good shape.

Goldfish weren't always gold; their wild kin are dark gray and olive-green. Goldfish are related to carp, so they have a rather unglamorous lifestyle, spending their time foraging in murky water for a variety of foods, including plants, insects, snails, and the eggs of other fish. The lovely colors and sometimes bizarre shapes of goldfish are the products of selective breeding conducted in China and Japan, where they are native.

A bucket, a bowl, a plastic bag, or a two-story-tall glass box can be an aquarium. A few of the millions of plant and animal species make excellent classroom aquarium organisms. But before we look at the organisms, it is important to think about the factors that make up their environment.

Water. Chlorine in regular tap water can be lethal to both goldfish and guppies. There are two ways to dechlorinate water. The first is to age the tap water by letting it sit in an open container for at least 24 hours. Chlorine dissolved in the water escapes into the air. Or add dechlorinating chemicals (included in the kit) to tap water. In some water systems, chloramine, a newer additive, is used in place of chlorine, and it will not leave the water when exposed to air. You must use water conditioners that specifically say they remove chloramine. It might be beneficial to ask at your local pet store or aquarium store just what is recommended in your area to make the water safe for fish. Set aside a pitcher of water to age, so that you will have it ready to maintain the water level of the aquarium. Keep your aquarium covered to reduce evaporation and to keep dust out and fish in.

The water in an aquarium will be fine for extended periods of time. Aged or treated tap water should be added to maintain the proper level, and about once a month half of the water should be removed and fresh water added in order to reduce the concentration of nitrogen-containing chemicals, the excretory products of the animals.

If a fish dies, or if too much food is put into your aquarium, change the water immediately. If you don't, bacteria will proliferate, taking advantage of the bounty of food. The result will be a putrid smell and danger for your fish and other aquarium animals. The bacteria will quickly deplete the oxygen supply in the aquarium, and the animals will suffocate.

Temperature. Unless you get fish that are specifically identified as tropical fish, it will not be necessary to obtain an aquarium heater. For the classroom it is best to stick to temperate-water organisms—they are so much easier to maintain. In fact, it is more important to keep your aquarium from getting too warm. Warm water holds less oxygen in solution, so aquatic organisms are more comfortable in cooler water. Keep your aquarium away from direct sun except for specific purposes.

Aquarium care. Goldfish don't place many demands on the aquarist. They need unpolluted water, but it is not necessary to provide extra oxygen with an air pump. You may experience some mortality when you first introduce new fish into your aquarium, but this is often due to transportation stress. As long as the fish are not crowded, they will be able to get enough oxygen just from what is dissolved at the surface of the water. To avoid crowding, do not exceed one feeder-size (3 cm) goldfish per liter of water for any extended length of time. You should be able to put six to eight guppies in a basin aquarium.

Food. Goldfish will eat a wide variety of foods, but the most convenient is a commercial flake food. This kind of food floats, and the fish will quickly learn to come to the surface to eat. The most important thing about feeding is not to overfeed! Feed your fish once a day as much food as they will consume in 3–5 minutes. Too much food left in the aquarium will foul the water. Fish-feeding cakes—compressed food that disintegrates slowly—are available at pet and aquarium stores if you need to leave the fish unattended for more than 3 days.

Feed the fish when students can observe the feeding behavior. Goldfish like to eat insect larvae, worms, aquatic plants, and snail eggs (all of which they eat in the wild) as well as commercial food. Guppies also eat commercial fish food, as well as finely chopped fish, tubifex worms, earthworms, and Daphnia.

Reproduction. Goldfish are very prolific in nature and in special breeding ponds, but don't expect any offspring in the classroom. They need lots of plants and other cover to propagate successfully. If they did lay eggs in the aquarium, they would doubtless eat all of their own eggs during their incessant foraging for food morsels. Goldfish can grow to be 40 cm (16") long and may live more than 10 years. Be prepared for an extended stay when goldfish move into your room.

Guppies are small fish that bear live young. The feeder-guppy females are larger and usually a uniform beige or silver gray. Their abdomens become quite large when they are gravid (carrying young). The males are smaller and have longer, flowing tails. Males are the ones with spots of multiple colors. Fancy guppies that have been bred for showy colors can be dazzling.

Guppies are quite prolific and will probably give birth during their stay in your classroom. In fact, you may observe the arrival of baby guppies a day or two after the adults are put in their basin aquarium. The stress of transportation may induce a gravid female to release the babies. Adult guppies will eat the young, so you should supply the aquarium with plenty of Elodea in which the babies can hide, or move the adults to a separate tank. Students will enjoy watching the baby guppies grow.

What to do when the fish arrive. Float the unopened bag in aquarium of dechlorinated or spring water for about 15 minutes to equalize the temperature. When temperatures are equal, pour contents of bag through a dip net into another container and transfer fish from net to the aquarium. Discard shipping water. DO NOT USE CHLORINATED TAP WATER!!!

Maintain aquarium at room temperature out of direct sunlight, adding and/or changing water with treated water as necessary to reduce the concentration of nitrogen-containing chemicals naturally occurring in the water.

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The land snail is one of nature’s marvels. But many of its finer attributes go unrecognized because of its reputation as a garden raider. Because it takes a toll on our spinach, cabbage, and lettuce as it goes about its business of survival, we find ourselves in a conflict relationship. In the classroom, however, traditional animosities are put aside in the interest of learning more about the diversity of life.

Land snails are gastropods, whose members also include aquatic snails (including marine snails) and slugs. The name means stomach-foot. This makes a degree of sense as the whole clan gets about by gliding on a muscular structure on the bottom of the abdomen, called the foot. The action that produces motion is a well-coordinated, wavelike contraction of muscles on the bottom of the foot that propels the gastropod smoothly forward over just about any surface. The action is not fast by human mobility standards, but you and your students will be amazed by how far snails can travel when your back is turned for what you think is just a moment. A determined snail can easily cover a meter in 5 minutes, so in the course of an evening a snail can travel the length of a football field and back. If the lid came off your terrarium in the evening, you can figure out how far and wide those snails might range in your classroom.

Land snails have several characteristics that make them easily identifiable. They have a single shell, usually coiled, that is a combination shield and humidor. The hard shell resists the efforts of predators and provides a haven during dry times. Snails are a moist gang, and if a snail cannot find a watering hole to renew its water supply, it will retreat to a protected nook, withdraw into its shell, and seal its shell to a solid surface. The snail will lapse into dormancy until rain, dew, or a garden sprinkler once again moistens the environment. This passive state, rather like hibernation but initiated by dry rather than cold, is called estivation.

One indication that snails have been active is the telltale slime trail. Garden snails produce a layer of mucus on which they slide. This makes it easy to track their movement, but also saddles them with a reputation for being yucky. Students may find this fact a bit repulsive at first, but will quickly forget it when they become absorbed in observations of these fascinating creatures.

Most land snails have interesting projections on the fronts of their heads. Students will identify them as feelers or antennae. They will see two long ones on top of the head reaching up, and two smaller ones reaching down. Technically they are tentacles, but “feeler” is a pretty good description of their function because they are touch sensitive. The two longer ones have light-sensitive organs at their tips, making them the snail’s version of eyes, although their function is limited to light perception rather than image generation. The shorter tentacles feel, taste, and smell the environment in the never-ending search for food and water, and in constant vigilance against dangers.

The snail’s mouth is on the bottom of the head right up by the short tentacles. Inside the mouth is a specialized eating tool, the radula. The radula is a muscular structure covered by thousands of tiny, sharp teeth. The snail eats by pressing the radula against a leaf or other desirable bit of vegetation and rasping it to scrape away small particles. This action can be seen if students feed a hungry snail some lettuce or apple.

Most other interesting snail structures are hidden inside the shell, but some can be observed with patience and perhaps a flashlight. Snails breathe by taking air into a visceral cavity that is richly supplied with blood vessels—the snail’s version of a lung. When the snail extends from the shell, the access pore can be seen opening and closing just below the margin of the shell on one side. Also, the snail’s heart can be seen pumping blood by placing a snail on the lens of a flashlight and carefully looking through the translucent shell.

The shell itself is an excellent piece of work. The colors and patterns are lovely, and the coil is a masterpiece of efficient construction. Snails grow by laying down new material around the edge of the roughly circular opening. By extending the length and diameter of the living quarters, the snail can grow and still retreat into its shell as needed. The shell is rich in calcium, so snails need a continual supply in their diet. In the classroom calcium is available from plain chalk or a piece of cuttlebone in the snail terrarium.

Most land snails are hermaphroditic, holding under one shell both male and female reproductive potential. However, snails must mate in order to fertilize each other’s eggs. Eggs, the size of BBs, deposited in soil, will hatch in a few weeks into perfectly formed little snails, fully mobile, ready to ravage your garden.

What to do when they arrive. The largest and friendliest land snail for the classroom is the escargot snail that is naturalized in California, Helix aspersa. If you live in a region where Helix has become established in local gardens, collect them locally. If you cannot collect them locally, order them from Delta Education. Land snails are quite hardy and can survive for many days with little food or water. In your classroom, they will live in two clear terrariums with covers (the same type of basins as used for the hydroponic plants). Once the snails arrive, place moist paper towels on the floor of each terrarium and spray the interior walls with water. Distribute the snails into the terrariums and provide a few small pieces of carrot or other vegetable for them to eat. Snails are strong! Secure the cover with two large rubber bands stretched around the terrariums.

Maintenance. In a natural habitat, land snails eat leaves, mushrooms, fruit, and many other kinds of plant material they find. In the classroom, they must be fed and their habitat must be cleaned. Here's the weekly care and feeding routine.

The question of what to do with the snails when the investigations are complete is a sensitive one and in part is determined by where and how you obtained the land snails. Potentially, the best solution is to keep them in the classroom and institutionalize their care, continually creating an ever more complex and interesting environment for them to live in. Continue informal investigations, particularly watching for life cycle. If you obtained the land snails from a supplier out of state with a USDA permit process, you must comply with the federal regulations on what to do with the snails. For snails that are not collected locally, release into the environment is never an option. If no other option is possible, the most humane thing to do is euthanize the snails by collecting them in a bag and placing them in the freezer. Then dispose of them in the trash.

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Many kinds of aquatic snails make excellent additions to an aquarium. All snails have spiral shells that get bigger toward the opening as the snail grows. The snail secretes new shell around the opening and moves in, abandoning the narrow reaches at the tip of the spiral in which it lived as a youth.

The muscular part of the snail that protrudes from the shell is the foot. Its mouth is on the foot right where a human’s foot has a couple of toes. Because of this interesting structure, snails are called gastropods, which means stomach (gastro) foot (pod). The snail scrapes algae from the surfaces over which it travels. A few snails in your aquarium will graze on the algae that grows on the sides and make it possible to see what’s going on inside.

Snails lay gelatinous globs of nearly transparent eggs. These may be stuck to plant material or the sides of the aquarium. After a couple of weeks, they will hatch, and the tiny larvae will swim freely around the aquarium. Soon they begin to grow a shell, which weighs them down and makes them pedestrian. You may find your aquarium swarming with tiny snails. Snails are quite cooperative about providing opportunities to observe their life cycle.

What to do when they arrive. Immediately upon arrival, open bag and place in cup or similar upright container to prevent tipping. Rinse snails with dechlorinated or spring water prior to transferring to aquarium. Snails will feed on algae or decaying plant matter naturally found in the aquarium.

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Worms are a varied lot. You may have heard of roundworms, flatworms, tapeworms, earthworms, and who knows what other kinds of worms. None of them conjures up a particularly warm or pleasant feeling in most people. Worms have low reputations in human circles, often associated with some not-so-pleasant circumstances. But this activity may turn all that around as you dig into the subject of earthworms.

Earthworms are members of the phylum Annelida, or ringed animals. They are fairly simple life-forms, put together from a number of disklike segments stuck together like a long flexible roll of coins. Earthworms have no internal skeleton like a fish, no hard protective exoskeleton like an insect, and no shell into which they can withdraw. Worms are flexible, elongated bundles of muscle, uniquely suited for life underground.

The characteristic wriggling of earthworms is accomplished by the contraction of two kinds of muscles. When the short muscles that circle each segment (like lots of rings on a finger) contract, the worm gets thinner and longer. When the long muscles that connect all the segments contract, the head and tail are pulled toward each other, and the worm becomes short and fat. Depending on which end of the worm is anchored, the worm can move along the surface of the ground or through its burrow effectively in either direction, head first or tail first.

Earthworm organs are quite different from ours, making it possible for them to live their very different lifestyle efficiently. Earthworms have five pairs of simple hearts that pump blood throughout the body. They have no lungs. Instead the blood flowing close to the worm's surface absorbs oxygen and releases carbon dioxide directly through the moist skin (called the cuticle). For this reason earthworms can live for some time in water if the oxygen supply is adequate. They don't drown per se, but they may suffocate if the oxygen content is low. This is why worms leave the soil and crawl out on the sidewalk during a heavy rain—they are seeking oxygen. Earthworms are not adapted to feed in water, however, so they would starve to death in due course.

Instead of a nose, ears, and eyes, earthworms have a nervous system throughout their bodies that controls actions in response to environmental stimuli, such as vibrations, heat, cold, moisture, light, and the presence of other worms. They have no brain, however, so worms do not ponder their lowly lot in life, nor do they plan a strategy for obtaining their next meal or crossing the sidewalk safely.

Reproduction. Like all animals earthworms have effective strategies for begetting their own kind. With earthworms it is not a matter of boy meets girl, but rather a simpler matter of worm meets worm. All worms carry two sets of sexual organs, but they cannot fertilize their own eggs—mating is still a necessary part of reproduction. Mature earthworms have an enlarged band some distance from the head. This enlarged clitellum plays an important role in reproduction.

In mating, two worms approach each other nose to nose. With their bodies touching, they slide past each other until their heads are a bit past the clitellum. Both worms pass sperm through an opening located between the head and the clitellum, into a temporary holding receptacle in the other worm. The two worms separate. The clitellum secretes a liquid that solidifies into a flexible tube. As the tube lengthens, the worm backs out of it. Soon the tube covers the front part of the worm. The worm lays a few eggs inside the tube, deposits some of the stored sperm, and withdraws from the tube, leaving the eggs and sperm inside the tube. The ends of the tube pinch off to form a cocoon, and the whole thing shrinks to a tidy package about the size of a fat grain of rice. The cocoon is left alone sitting on or just under the surface of the soil. The worm continues to produce cocoons until the sperm is used up. Cocoons are durable, can overwinter in cold climates, and can wait out hot dry spells in arid environments. After 3 weeks (ideal conditions) or longer the cocoon opens, and out sallies the next generation.

Food. Earthworms feed on decomposing organic material, mostly vegetation, from the surface of the soil and within the soil itself. In the process of burrowing and feeding they process tons of soil in a typical pasture or garden, improving the quality of soil for plants and other animals. There are some 1800 species of earthworms worldwide. Some are tiny, no more than 2 cm (1”) at maturity. At the other end of the scale are the Australian giants that average about 3 m (10’) in length, and the record holder, a South African gargantuan measuring 7 m (22’) in length. Not to worry—the largest earthworms in North America are the common night crawlers, which can reach a length of little more than 30 cm (12”).

What to do when they arrive. Worms may be kept in shipping container for short periods. Upon arrival, mist with water to moisten, but do not make soil wet. Worms can be kept in the refrigerator for short periods of time. To maintain worms for a longer period of time, keep at room temperature in diffused light, feeding crushed dead leaves or cornmeal sprinkled over the surface of the soil. Add rich soil (preferably humus) as needed, and remove any mold as it appears.

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Iso is Greek for "similar or equal." Pod means "foot." Put them together and you have the isopod, an organism that has an equal number of feet or legs on both sides with all legs similar to one another. Isopods have 14 legs that all function the same. This distinguishes them from closely related organisms that have legs that are modified to perform different functions, such as walking, feeding, feeling, grasping, and so on.

The many different species of isopods around the world share certain characteristics. Isopods are crustaceans, distant kin of shrimps, crabs, and crayfish. Like all crustaceans, isopods have a segmented outer shell (seven overlapping plates) that provides a measure of protection from the environment and predators. Like their aquatic relatives, isopods get the oxygen they need to survive through gill-like structures located at the bases of their legs, rather than through lungs like most terrestrial organisms. That is why isopods must keep moist at all times—if they dry, they die.

Two kinds of isopods are of interest as classroom organisms. The genus Armadillidium (arm•uh•duh•LID•e•um) is known casually as the pill bug or roly-poly. It gets these names from its habit of rolling into a tight sphere when threatened or stressed. The pill bug has a highly domed shape, short legs, and inconspicuous antennae. When in its defensive rolled posture, it is hard for a predator to grip, and it is also more resistant to drying out.

Pill bugs move slowly and have a difficult time righting themselves if they roll onto their backs on a smooth surface. They range from light brown to dark gray or black. Often they have white, cream, or yellowish spots on their backs. The largest individuals of this kind of isopod can be 1 cm long, but most are 7 or 8 mm.

The second isopod used extensively in classrooms, genus Porcellio (por•sel•E•oh), is commonly called the sow bug or wood louse. These names are potentially confusing because Porcellio don't show a particular affinity for swine, nor are they lice. They are relatively flat with legs that extend a little bit beyond the edge of the shell, and they have powerful antennae to sense their environment. They move rather quickly and will use their long antennae and little spikelike tail projections to right themselves if they happen to roll onto their backs. Sow bugs come in a surprising array of colors, including tan, orange, purple, and blue, as well as the usual battleship gray. Their size is similar to that of the pill bug.

In the wild, isopods are not usually seen out and about. They are members of that large category of animals known descriptively (not taxonomically) as cryptozoa, or hidden animals. They are most often found in layers of duff and leaf litter, under rocks or logs, or burrowed a short distance under the surface of the soil. The environment they seek is moist and dark, in or near dead and decomposing wood and other plant material. The former is their main source of food, accounting, perhaps, for their common name of wood lice. Isopods are not, however, above eating fresh strawberries and carrots, making them a minor pest in the garden.

Life cycle. There are both male and female isopods, but only another isopod can reliably tell them apart. After mating, the female lays several dozen eggs, which she carries in a compact white package on her underside between her legs. This package is a specialized brood pouch, the marsupium, in which the eggs develop for 3 or 4 weeks before hatching. A few days after hatching, a swarm of fully formed, minute isopods strike out into the world. They are nearly invisible at first but soon grow to a size that can be seen by the unaided eye. Like all crustaceans that carry a hard outer shell, isopods must shed their shells in order to grow. In the molting process the shell is cast off, and the new soft shell underneath expands before hardening. Interestingly, the whole shell is not shed at once; first the rear (posterior) shell segments are shed, and 2 or 3 days later the front (anterior) ones fall off.

What to do when they arrive. The shipping container contains damp paper to provide moisture. Upon arrival, mist paper slightly. Food should be removed if it shows any sign of mold and replaced with sliced carrot, potato, or apple. Pill bugs and sow bugs can be kept in the shipping container for a few days until ready to use in class. Moisten the paper towels as necessary.

If you are keeping them for a longer period of time, place them in a terrarium with rich, moist soil. Place moist paper towels in the container to provide humidity. Continue to add vegetables, replacing them as necessary to control mold. Keep container at room temperature in low light.

Classroom habitat. Isopods are excellent classroom animals—they exhibit interesting behaviors, they are small but not tiny, they don’t bite, smell, fly, or jump, and they are easy to care for. Isopods can live in just about any vessel, from a recycled margarine tub to a 50-liter aquarium. If the container is smooth-sided, it doesn’t even have to be covered, because isopods can’t climb smooth surfaces at all. A layer of soil covered with some dead leaves, twigs, and bark is great, but isopods will be comfortable with some paper towels or newspaper laid on the soil. They do like to have some structure to crawl under.

Food and water. The most important thing to remember is that the soil must be kept moist at all times—not wet, but moist—so that the isopods don’t dry out. A chunk of raw potato in the container with the isopods serves as a source of both food and moisture. Otherwise they will eat the decomposing leaves and twigs or the paper towels and newspaper.

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