In 3rd, 4th and 5th grade the knowledge and skills statements for life science address how live organisms go through processes and structures that help them to survive in their environments. One such process is metamorphosis which is addressed in the following standards:
- 3.10 C investigate and compare how animals and plants undergo a series of orderly changes in their diverse life cycles such as tomato plants, frogs and lady bugs
- 4.10 C explore, illustrate and compare life cycles in living organisms such as butterflies, beetles, radishes or lima beans
- 5.10 C describe the differences between complete and incomplete metamorphosis of insects
The word metamorphosis when broken down means, meta: changing, morph: shape, osis: the process of. This word is used to describe animals that go through a physical structure change during its lifetime. This could be a complete structure change, like larvae to adult creature, or a partial change like gaining body parts such as wings as an adult. Did you know that the majority of the animals here on earth go through some type of metamorphosis during their life cycle? This is because the majority of the animals on this earth are insects. Biologists believe insects have evolved to experience metamorphosis as an aid to survival. When insects are in their different stages of metamorphosis, they do not compete for the same food source and fulfil a different niche in their environment. For example, caterpillars do not compete for nectar with butterflies because their food source is the leaf of plants, which doesn't compete with their adult counterparts and so on.
Complete Metamorphosis
A complete metamorphosis is a complete structure change that happens within a creature's life time. When we talk about complete metamorphosis we usually mean insects that go from an egg to a larva and then pupa stage before becoming an adult. During the larval stage the larva will probably go though several molts. A molt is when the insect sheds its outer shell or exoskeleton in order to grow larger. That is because animals with exoskeletons have to molt because once an exoskeleton hardens it cannot grow. When a larva reaches a large size it will go into its pupa stage. In this stage the animal is vulnerable because it can hardly move. Inside the pupa the tissues of the larva is broken down and reshaped into that of the adult. Since the pupa is vulnerable it is usually camouflaged within the environment or buried underground until it is ready to hatch. Not all larva reach a large size before forming a pupa, absence of food or a change in temperature can also trigger a pupa stage. Judging by the amount of eggs produced by insects at a time, we can venture to guess that both larvae and pupa stages will have quite a few insects that don't make it to adulthood.
Incomplete Metamorphosis
An incomplete metamorphosis is a partial structure change that happens within a creature's life time. During incomplete metamorphosis the juvenile hatches from the egg already looking like the adult. This is called the nymph stage. Nymphs will go through a series of molts until they reach a final phase in which they gain wings and the ability to reproduce. Once the insect gains it's wings it will no longer experience molts and will stay that size until it dies. So what is missing in an incomplete metamorphosis? The pupa stage. If the insect doesnt have a pupa stage, but does gain a body structure change like gaining wings, then it is incomplete metamorphosis.
Insects that Have Complete and Incomplete Metamorphosis
As with any science lesson, reading about metamorphosis is not as exciting as actually watching it happen in the classroom. The easiest metamorphosis to witness are insects because, to put it simply, those are the easiest to teach and the easiest to find. However, if you are a little queasy about our 6 legged friends, you really want to think about how you are going to work with them as well as how you will react to having them in your lab or classroom because not only can animals smell fear, so can kids. Not everyone is keen on handling insects, and there are different levels of interaction that kids and teachers can have with the animals to get the job done
Insect recommendations: Complete Metamorphosis
When you gaze up at the list above you will notice that there are insects up there that you will think, "that's not so bad" and then there are some that are absolutely NOT candidates. I recommend butterflies, darkling beetles and lady bugs as the insects of choice for the classroom. All three of these are easy to order for the classroom but you will need some materials such as terrariums, food source, a place to make a pupa and a cage to fly around in once the metamorphosis has happened.
Lady bugs: Lady bugs are listed in the such as statement in 3.10 C, but where do you get lady bugs from? Lady bugs can be purchased at garden centers in the spring to help control aphid populations, however these lady bugs are already adults. It turns out lady bugs are actually hard to breed in captivity, but there is one vendor that actually raises lady bug eggs and larva and that is INSECT LORE. Insect Lore carries an all in one terrarium for raising lady bugs called Lady Bug Land, which runs about $24.95 plus shipping. The terrarium comes with a live material specimen card, that, when you mail it in, you will be shipped live lady bug larva and food for the lady bugs. I have done this activity before with students and it is wonderful. The kids get a kick out of watching the lady bugs larva eat and go through their stages. It is also the most hands off of all of the terrarium activities because the container hosts the whole process and the teacher need only keep the small sponge wet and then feed the adult lady bugs some wet raisins after they hatch from the pupa. The only drawback from Lady Bug Land is that the refills need to be purchased from year to year and even though many science companies might sell Lady Bug Land, only INSECT LORE sells the refills, so if you are interested in raising lady bugs, make sure to make INSECT LORE a vendor at your district.
Insect recommendations: Incomplete Metamorphosis: Going back to the list above you will notice that there are even fewer insects up there that you will think should be candidates for incomplete metamorphosis. I recommend crickets and praying mantises.
Activities You Can Do with Complete and Incomplete Metamorphosis
Asking Questions: I always like to start an animal observation with asking questions. When students pose questions about the animals they will always hit the most important concepts such as life span, adaptations, predators, environment and basic needs. Use these questions that they generate to drive their research.
Collecting Data: As they are doing their research, have them collect their information in a table that they design. Depending on the insect that you have chosen, you can also study populations. For instance, how many mealworms have turned into pupas? How long does it take for the pupa to become an adult? What is the survival rate? These are all great questions to chart and graph.
Drawing and labeling charts: Have the students draw or take close up pictures of the insects as they are going through their changes. Have them label body parts and describe the structures.
Mnemonics: Did you know that kids can remember a complete metamorphosis by using the acronym of E.L.P.A.S.O. (Egg, Larva, Pupa, Adult, Start Over) We also have them memorize the incomplete metamorphosis as ENASO, (a nonsense word that sounds like spanish) Egg, Nymph, Adult, Start Over.
Testing Tips: Many times on the test they will show diagrams of life cycles of insects, but some will include stages of molts. Molts are just the insect shedding its exoskeleton. When teachers teach complete metamorphosis as more than 3 steps, kids will mistake an insect with several molts as an insect with complete metamorphosis. Remember that the complete metamorphosis has a pupa stage. All larvae and nymphs will molt to grow larger, but only insects with a pupa stage are considered a complete metamorphosis. Also, with the exception of insects like dragonflies, most nymphs look exactly like the adult except that they are missing their wings.