Insects and Plants
Plant and Animal Care

Students investigate the following animals in the Insects and Plants Module

Mealworms
Milkweed Bugs
Silkworms
Painted Lady Butterflies

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.

MEALWORMS

The mealworm is not a worm; it is a larva. Any similarity to a true worm is incidental. mealworm larvae are golden yellow and have 13 segments—a head, three thoracic segments, and nine abdominal segments Mealworm larvae are the counterpart of the familiar caterpillar in the butterfly story. They pull themselves around on six stubby legs, one pair on each thoracic segment.

Mealworms are the larval stage of darkling (aka Tenebrio) beetles. Beetles, along with all their other insect kin (true bugs, flies, bees, wasps, ants, on and on), are members of the phylum Arthropoda, a word meaning jointed legs. Like all members of their phylum, insects wear their skeleton on the outside like a suit of armor. This is practical when they are under attack, but very inconvenient when they are trying to grow. Arthropods solved this problem by molting (shedding) this outer shell-like cuticle periodically. Immediately following the molt, the soft white larva expands before the new larger cuticle hardens. For mealworms this process repeats five times over a 2-month period, after which the larva is about 3 cm long. The final larval molt reveals the next stage, the pupa.

Life cycle. Darkling beetles follow a life history known as complete metamorphosis. Like butterflies and moths, they go through four distinct stages during their life cycle. A female beetle lays eggs, as many as 500 in her brief lifetime of a month or two. The eggs are about the size of the period at the end of this sentence. After a couple of weeks the equally tiny larvae emerge from the eggs. The larvae are known as mealworms, but of course they are not true worms. The larvae are golden yellow and have 12 body segments. They are the counterpart of the familiar caterpillar in the butterfly story. Mealworms pull themselves around on six stubby legs that are all crowded at the front.

The larvae seem to have two purposes in life: eat and grow. Beetles are arthropods, and like all members of their phylum they wear their skeleton on the outside like a suit of armor. This is very practical when they are being attacked, but very inconvenient when they are trying to grow. The arthropods have solved this problem by shedding (molting) their shell periodically. Immediately following the molt the soft, white larvae expand before the new larger shell hardens. This process may repeat half a dozen or more times over a 3-month period, after which time the larvae are about 2 cm (3/4") long. The final larval molt reveals the next stage, the pupa.

The pupae don't eat and they don't move except for a twitch or two when disturbed. Inside, however, the mealworm is turning into a beetle, much the same as a caterpillar turns into a butterfly while sequestered inside the chrysalis. In 2 or 3 weeks the pupa splits open and out walks a beetle, white at first, but soon turning to brown and finally black after a day. The beetles mate and lay eggs, and the cycle repeats.

Habitat and food. Mealworms and darkling beetles are rarely seen in the wild, but when they are, it is likely to be in a field where wild grasses flourish and seeds are plentiful. They are most often found in barns, grain storage facilities, and food preparation areas. This organism has benefited by living close to human enterprises, because we unwittingly provide a much better environment for the success of mealworms than could be found in the natural world. For this reason mealworms have become a minor pest in grain storage areas.

Mealworms and darkling beetles 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 extremely easy to care for. Mealworms live right in a container of their food source: bran, cornmeal, rolled oats, breakfast flakes, or chick starter mash. All are excellent foods, but bran and chick starter are recommended. The food must be kept dry. Mealworms can go through their complete life cycle without any added water (they are very efficient at extracting water from the food), but it is recommended that small bits of apple, potato, or carrot be added from time to time.

Mealworms should be kept in large, relatively flat containers. They seem to thrive best when the colony has a large surface area. Keep the bran about 2 or 3 cm (±1") deep in a basin, bus tray, aquarium, or plastic shoe box. If the container sides are steep and smooth, it is not necessary to keep the container covered. Adults and larvae seem to prefer hiding under bits of paper or light cardboard; the pupae give no indication that they care.

The mealworm's preferred environment is very dry, moderately warm, and dark. A bit of apple provides extra moisture for the mealworms and seems to stimulate rapid growth. As the temperature increases, so does the rate at which mealworms advance through their life cycle. Under ideal conditions, in a classroom, the complete life cycle can take place in as little as 3 months, but more likely it will take 4 months. Cold slows the process almost to the point of suspended animation. Mealworms can be put into the refrigerator (not the freezer) for periods of time to stop metamorphosis.

In addition to providing reliable opportunities for observing a complete life cycle in the classroom as in the Insects and Plants Module, mealworms can also be used for other activities. In the Environments Module their response to various environmental factors is investigated. Mealworms can be used for structure/function observations and behavior investigations. And they are just nice to have around to remind us that life on earth takes a seemingly endless variety of forms, and that part of being human is to have compassion and respect for all life.

Food and Water. The mealworm culture must be kept dry. Mealworms can go through their complete life cycle without any added water (they are very efficient at extracting water from their food), but it is recommended that moisture continually be provided in the form of small bits of apple, sweet potato, or carrot. Otherwise the larvae and adults may attack each other in search of additional moisture. If carrot or sweet potato is used as the moisture source, the frass will be orange, adding evidence that the granules are waste rather than eggs.

Mealworm Homes. Large cultures of mealworms (200 or more) should be kept in large, relatively flat containers. They seem to thrive best when the colony has a large surface area. Keep the bran 5–10 cm (2–4") deep in the clear plastic basin provided in the kit. If you want to expand your mealworm activities, any basin, bus tray, or old aquarium will do. If the container sides are steep and smooth, it is not necessary to cover the container.

The mealworms's preferred environment is very dry, moderately warm, and dark. As the temperature increases, so does the rate at which mealworms advance through their life cycle. Under ideal conditions the complete life cycle can take place in as little as 3 months, but more likely it will take 4. However, students should be able to see their mealworms advance through the three important stages of larva, pupa, and adult in 4 to 6 weeks if the larvae are large and well advanced at the time they are introduced.

Mealworms and darkling beetles are rarely seen in the wild, but when they are, it is likely to be in a field where wild grasses flourish and seeds are plentiful. They are most often found in barns, grain storage facilities, and food preparation areas. This organism has benefited by living close to humans, because we unwittingly provide a much better environment for them than can be found in the natural world.

What to do when they arrive. Mealworm beetles are shipped in a container with a "breathing" cap to provide air. They need no special care but should be used as soon as possible, as they have a rather short life span. Keep beetles at normal room temperatures in low light. Store in a cool place at 45 to 65º F out of direct sunlight. At warmer room temperatures, larvae will soon pupate. Cover loosely with a paper towel to provide crawling space. Add slices of potato or carrot for moisture and add a substrate of bran for food. Replace as necessary or if it becomes moldy.

 

Mealworm Life Cycle
Stage
How long?
Food
Moisture
Other information
Egg 7–14 days      
Larva 30–90 days Bran Apple 5 molts occur
Pupa 10–20 days      
Adult 5–10 days Bran Apple Death: 30 days
Egg The cycle continues.

 

Back to top

MILKWEED BUGS

Milkweed bugs are true bugs; beetles, moths, flies, and butterflies are not. Bugs have the usual complement of structures that they share with just about all other insects: six legs, three body parts (head, thorax, and abdomen), and two antennae. True bugs (order Hemiptera) do not have mouths for biting and chewing food—they have a tubelike beak for sucking fluids. The milkweed bug in nature sucks nutrients from milkweed seeds, but those in the classroom have been bred to feed exclusively on sunflower seeds.

Another characteristic of bugs generally and milkweed bugs specifically is the stages they go through from hatching to maturity. Bugs go through simple metamorphosis. The insect emerges from an egg looking like a tiny version of the adult, with slight differences in body proportions and incompletely developed wings. The immature bugs are called nymphs. Newly hatched nymphs are analogous to the larvae of insects that go through complete metamorphosis, in that their prime directive is to eat and grow. As with all insects, in order to grow the nymphs must molt periodically. Just after molting the bug is creamy yellow with bright red legs and antennae. Within a few hours the body turns dark orange, and the legs and antennae resume their usual black color. The crispy little molts can be seen in the milkweed bug habitat about a week after the bugs hatch. Students may think their milkweed bugs are dying or that spiders and ants have invaded the habitat. It may take a while for students to figure out what the molts really are.

Life cycle. Milkweed bugs advance through five nymphal stages (instars) as they mature. Each molt produces a larger nymph that is more completely developed. As the bugs grow, the dark wings appear on the backs of the bugs as black spots. Other black markings start to appear and eventually develop into the characteristic patterns of black and orange by which the adults of the two sexes can be identified. The last molt reveals the adult. There is no pupal resting stage as in insects that undergo complete metamorphosis—the large nymph simply molts, and away walks the adult.

Milkweed bugs continue to feed as adults, inserting their long beaks into sunflower seeds to suck out oils and other nutrients. Mating is easily observed, as the two mating bugs remain attached end to end for an extended time. It is possible to distinguish female and male adults by body markings. Look on the ventral (belly) side of the bugs. The tip of the abdomen is black, followed by a solid orange segment (with tiny black dots at the edges). If the next two segments following the orange band have solid black bands, the bug is a male. However, if the segment following the orange band is orange in the middle, making it look like it has two large black spots on the sides, followed by a segment with a solid black band, the bug is female. (See the Milkweed Bug Male and Female poster.) Males tend to be smaller than females. Look for mating bugs to identify males and females—there will always be one of each in such pairings.

Several days to 2 weeks after mating, the female lays a cluster of 50 or more yellow eggs (which turn orange fairly quickly) in a wad of cotton. The eggs can be removed to a new culture container or left in the habitat to continue the life cycle.

Milkweed bug habitat. Culturing milkweed bugs is fairly easy. The bugs require no soil or green plant material. Just about any container is suitable for a habitat. Because milkweed bugs can walk on any surface, including smooth plastic, glass, metal, wet surfaces, and all textured surfaces, the habitat must be closed tightly, and the ventilation holes must be tiny so the first instar nymphs can't escape.

We suggest a plastic zip bag for the habitat container. Use a pin to poke a hundred holes in the bag, and install a water container in the bottom. To add interest, put a branch in the bag and attach a bundle of raw, shelled sunflower seeds and a cotton ball to the branch. Hang the bag from a paper clip next to a wall out of direct sunlight.

Maintenance. Maintenance is minimal. Keep an eye on the water level, and when it gets low after 3–4 weeks, add water and perhaps replace the wick. A new bundle of 20 to 30 sunflower seeds each month should be adequate for a modest culture of 25 bugs. The culture may start to look a little messy after a month as little brown spots of waste appear on the walls of the bag and the molts start to accumulate. Transfer the branch, water fountain, and bugs to a new bag to renew the aesthetic appeal of the culture.

Ordering milkweed bug eggs. Milkweed bug eggs must be ordered from a biological supply company. Specify at the time of order when you want the eggs delivered. See the Materials folio for more information about obtaining insects. Conduct Part 1 as soon as the eggs arrive—they will hatch in a week or less after you receive them. Color is an indicator of maturity. If the eggs are pale to school-bus yellow, it will be a few days until they hatch. If the eggs are pumpkin-orange to red, they will hatch in the next couple of days.

What to do when they arrive.

End the life cycle. As long as the four needs are attended to, new generations of milkweed bugs will continue to flourish in the habitat. At some point you may want to end the cycle. Although the bugs would probably soon perish if released into the environment, it is not suggested that you do so, as they were not originally from the environment. Place the bag in the freezer overnight to kill the bugs; discard the bag in the trash.

Back to top

SILKWORM MOTHS

Silk is a natural fiber of exceptional strength, texture, and luster. When silk fibers are spun into thread and woven into fabrics, the result is an exquisite commodity. Silk was first made in China, and for centuries the methods of production were cloaked in secrecy, so valuable was the technology to those who controlled the art and industry of silk making. Eventually, however, the secret and the organisms escaped the control of the Chinese, and thriving silk industries were established in Japan, Arabia, and Spain. Even today, with the vast array of synthetic fibers that rival silk in many ways, the demand for the real thing is still high.

Although the larvae of most moths and butterflies produce silk, that produced by Bombyx mori is the silk of commercial importance. The silkworm moth lived in nature 4500 years ago when the Chinese silk industry was in its infancy, but as years passed, the insect became so domesticated that it can no longer fend for itself in the wild. It can no longer fly, move more than a few centimeters to find its food, or defend itself against predators.

As the silkworm prepares to pupate, it spins a protective cocoon. About the size and color of a cotton ball, the cocoon is constructed from one continuous strand of silk, perhaps 1.5 km long (nearly a mile). If the silkworm were allowed to mature and break through the cocoon, the silk would be rendered useless for commercial purposes. So the encased insect is plunged into boiling water to kill the inhabitant and dissolve the glue holding the cocoon together. The end of the silk is then located and the cocoon unwound onto a spindle to be made into thread.

Life cycle. A silkworm starts its life as a tiny egg laid by the female moth. The egg is just about this size: . The egg, laid in the summer or early fall, remains dormant until the warmth of spring stimulates it to start developing. When silkworms first hatch in the spring, they are tiny—3 mm or so (about 1/8")—and hairy. They require young tender mulberry leaves during their first few days. As they grow, they can eat tougher leaves, and late in their development they will eat any mulberry leaf you can supply.

The larvae advance through five stages of growth, called instars. The silkworm literally outgrows its skin five times, and molts its outgrown skin. With the first molt the silkworm loses its hairy exterior, and for the rest of its larval life its skin is soft and smooth.

Silkworms grow rapidly, eventually reaching the size of your ring finger. Then they spin beautiful oval white or yellow cocoons in which they pupate. After 2–3 weeks the creamy-white adult moths emerge from the cocoons. They clamber around, vibrate their wings rapidly, and mate, but they don't fly or attempt to escape from their container. During the adult phase of the life cycle, the silkworm moths do not eat or drink. After mating, the female lays a profusion of eggs, and the moths die.

Males and females look slightly different, and students will be able to tell them apart with a little practice. The female has a larger abdomen. The male has a much larger pair of antennae, which look like long rakes or comb-shaped eyebrows, and vibrates its wings rapidly to attract a female.

Silkworm Feeding Silkworms eat mulberry leaves; lots of them! But getting leaves in the late fall and winter months is nearly impossible as the trees are deciduous. In California, mulberry trees drop their leaves in November and sprout again in late March/early April.

If you are doing the Silkworm Investigation in the winter, there is an alternative food. With every order of silkworm eggs you will be sent a half-pound of dry silkworm chow. Preparation requires hot tap water and a heat-source such as a microwave oven or stove-top. Water is mixed with the dry powder and then brought to a boil. The resulting mixture is poured onto a sheet of cling wrap, cooled, wrapped, and stored in the refrigerator. When firm, the silkworm chow can be sliced and fed to the hungry larvae.

The cooked Silkworm Chow can be stored in the refrigerator for a month or two if kept in an airtight container. Each bag of the dry powder comes with detailed instructions on the back of the package. Make sure your hands are clean when handling the cooked chow as the silkworms are susceptible to bacterial problems if their food is not kept sterile.

But remember, if you are raising silkworms in the spring, summer or early fall, fresh leaves are the best food source. Ask the Kindergarten teachers to plant a mulberry tree during their FOSS Tree module and you'll be set!

If you are using mulberry leaves, the first 10 days the larvae will need catkins or young tender leaves, but after that the larvae will eat any leaf you can provide. Keep leaves in the refrigerator. Feed the silkworms once or twice a day.

Think about the timing of the investigation. The silkworm eggs must hatch when mulberry leaves and catkins (flowering portion of the mulberry tree) are available (see the above section for an alternate feeding possibility if mulberry leaves are not available). If you are not sure when mulberry trees begin budding in your area, ask a colleague or inquire at a nursery. See the background section for the Silkworms Investigation for more specific information.

Obtain silkworm eggs. Eggs of the silkworm must be obtained from a colleague who worked with silkworms last year, or ordered from a biological supply company (see the Materials chapter for more information about obtaining insects). Order 50 eggs. If you purchased eggs from a biological supplier, plan to conduct this part as soon as the eggs arrive, because they will hatch 1–2 weeks after you receive them.

What to do when they arrive. Purchased silkworm eggs usually arrive loose in a vial. working on a large piece of white paper, use the little paintbrush to divide the eggs into eight piles, and put one pile into each of eight vials. Cap the vials. Keep them in a warm place out of direct sunlight until you are ready to introduce them to students.

Eggs from a colleague may be stuck to paper. If this is the case, cut or tear the paper so that each piece has 10–15 eggs, and put the bits of paper into the vials.

Habitat. A shoe box is all that you need to make a silkworm habitat. Choose a place in the room where the silkworms will be warm but not in direct sunlight. Place the shoe box in an open plastic bag, or drape a sheet of plastic over the box. The idea is to reduce evaporation from the leaves a bit without developing a humid environment.

If the eggs are scattered all over the box, that is OK, but the larvae should be placed on a leaf. New larvae must be rounded up each day and delivered to a fresh mulberry leaf.

Larva. Silkworm larva are delicate at first and should not be handled for the first 2 weeks except with a tiny paintbrush. By the time the larvae are 2 cm (1") long, students can carefully pick up and gently hold them. The larvae seem to survive better if they are kept together in a single culture early in life—later they can be kept in pairs or small groups on students' desks.

Plan for spinning. Get a medium-size corrugated cardboard box and a couple of paper egg cartons. Open the egg cartons and attach them to the inside walls of the box. The silkworms will spin in the depressions in the egg cartons. The silkworms must all be in this box for spinning their cocoons. The time for this will be signaled by the first larva that starts to spin, either in your class habitat or, more likely, in one of the group habitats.

Prepare for silkworm moths. Once the larvae spin cocoons, they require no further care. The moths will emerge in a couple of weeks and can be handled by students. They do not eat or drink—they mate, lay eggs, and die.

Prepare for mating and egg laying. Get a large flat box, or cut a taller one down to about 10 cm (4"). Line the bottom with paper. As the adults emerge, move them to this new box. The moths will stay in the open box. The females will lay eggs on the paper, making them easy to collect.

Collect eggs. The eggs will remain viable for a year with minimal care. Seal them in a labeled zip bag and put them in the refrigerator (not the freezer!) as soon as all the moths have died. If you don't refrigerate the eggs, they will still hatch, but over an extended period of time instead of all at once.

Back to top

PAINTED LADY BUTTERFLIES

Painted lady butterflies can be purchased from a biological supply house as small fuzzy larvae—maybe as small as 1 cm (1/2") long. They arrive in a plastic container with a centimeter or two of green goop that looks like guacamole. The ventilated lid holds a piece of filter paper over the top of the container. Keep the lid and paper on the container at all times. The painted ladies will spend all of their larval days, perhaps 2 weeks or a little more, in the container eating the food layer, molting, and growing to a length of 4 cm (1-1/2") or a little more. They require no special attention other than to keep them in a well-lighted area, but out of direct sun and safe from temperature extremes. After the larvae are about 2 cm (3/4") long, it is all right for students to remove the larvae from the containers from time to time for close observation of structures and behaviors.

Life cycle. In due course the larva receives a biological message to climb to the top of the container, spin a little knob of silk onto the filter paper, and attach its rear end firmly to the knob. The larva hangs head down and assumes a characteristic J shape, indicating that pupation is only a few hours away. If you are vigilant, you might be able to observe the final molt as the fuzzy outer skin splits near the head to reveal the smooth, curiously molded, slightly iridescent pupa ensconced in its chrysalis. As the pupa writhes around, the skin is pushed up and off the body until it is a crunchy little nub pressed up against the paper. The painted lady lapses into a period of relative quietude, hanging motionless except for brief fits of wriggling, especially when disturbed. At this time the pupae attached to the paper should be moved to a larger cage.

For a week or 10 days the pupa undergoes dramatic physical and biochemical transformations. The chrysalis gradually darkens until it is dark gray-brown, and the orange color of the wings starts to show through. This is when you can expect the adult to emerge, which happens quickly. The chrysalis shell splits near the bottom (head end), and the butterfly reaches out with its legs and grasps the outside of the chrysalis. The head comes out, and then the abdomen and wings are pulled free of the chrysalis shell. The emergence takes a minute or less.

The fresh new butterfly clings to the chrysalis shell with its soft, crumpled wings hanging down. Over the next hour or two the abdomen pulses as it pumps fluid into the veins of the wings, expanding them to their fully extended shape. During this time the butterfly ejects a splat of red liquid. Students may be alarmed, thinking it is blood, but it is a waste fluid that the butterfly unloads as it prepares for its new life. In 3 or 4 hours the butterfly takes wing as a flying insect.

Maintenance. Painted lady butterflies don't require much as adults. They will drink dilute sugar solution and fly around looking for mates. Place the cage where sunshine will fall on it for a few hours each day. If mallow, a common weed in many parts of the country, is available, you can place a small bouquet of leaves in a vial of water. After the butterflies mate, they will lay eggs on the mallow leaves. If you want to raise a second generation of painted lady butterflies, provide mallow leaves for the larvae to eat.

After a month the adults will die, not because of any ill effects caused by captivity, but because that is their normal life span. Even though it is never advisable to release study organisms into the environment, if a painted lady butterfly "escapes," it will not be an environmental disaster—painted ladies are already well established throughout the country.

Order butterfly larvae. Painted lady butterfly larvae are available from several biological supply companies. They arrive in a container of food and will advance through their entire larval stage without ever leaving the container. They are usually sold three to five in a container. It is nice to have about ten larvae (two containers), but the activity will be a great success with one container. The larvae can usually be delivered about 2–4 weeks after you call in your order.

Use local larvae. If you have local painted lady larvae, or another species of butterfly larvae available, use them instead of commercially available larvae. You will need to research appropriate food sources for each type of butterfly larvae.

What to do when they arrive. Butterfly larvae are shipped with their own food in the shipping container. Warmer temperatures will encourage larvae to grow more quickly. Maintain container out of direct sunlight. No further care is necessary, as they will pupate within 7 to 10 days. (See above)

Prepare a feeding station. A butterfly feeding station can be made from a standard insect water fountain. Use a hole punch to make a hole in the center of the cap of a vial. Roll up an 8-cm (3") square of paper towel and push it through the hole in the cap. Push the vial into the plastic vial holder to prevent the fountain from tipping over.

Butterflies feed by sipping nectar through their long coiled proboscis. A substitute nectar can be made with sugar and water. Put 1/4 teaspoon of sugar in a vial and fill it with water. Attach the wick cap to the vial. Cut a crude flower from a piece of red or orange paper, make several criss-cross cuts in the center, and push the vial through. The flower will attract the butterflies and give them a place to land.

Provide mallow leaves (optional). When adults emerge, provide a bouquet of fresh mallow leaves in the cage. Use the hole punch to punch a few holes in a plastic cup lid. Fill the cup with water and snap on the lid. Stick leaves and small branches of mallow through the holes. Females will lay eggs on the mallow leaves.

Watch for egg hatching. The eggs hatch in a week or so, and it is possible to start the whole process over again. Larvae will thrive if you transfer them to fresh mallow leaves. They must be kept in a covered container because they are very mobile. A supply of mallow leaves can be kept in the refrigerator. If you do not want to let the eggs hatch, put them in the freezer for a few days to end the life cycle. Eggs, larva and adults should not be released into the wild as it can disrupt the local ecosystem.

Discuss death. Butterflies don't live long. After 3 weeks they will be tattered and tired. With luck they will have fulfilled their destiny by producing eggs. Discuss the inevitability of the death of the butterflies and that it is not caused by captivity or the result of any failing on the part of the caregivers. Butterflies just don't live very long.

Back to top