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Metamorphosis is the change of a young animal (a larva) into an adult. Butterflies and frogs both go through metamorphosis.

Some insects go through complete metamorphosis: egg → larva → pupa → adult. The pupa is an inactive stage. Butterflies, moths, beetles, bees, ants and flies develop like this.

Other insects go through incomplete metamorphosis: egg → nymph → adult. Nymphs look like small adults; they grow by moulting (shedding their skin). Grasshoppers, crickets, cockroaches and dragonflies develop like this.

Experiment: A frog's life to scale

1. Use the scale 1 cm = 1 week. Mark 'spawn laid' at 0 cm at one end of the strip.
2. Tadpoles hatch after about 3 weeks: mark them at 3 cm.
3. Legs begin about 16 weeks after hatching: how many weeks is that from the spawn? Mark it.
4. A frog is ready to breed at about 2 years (1 year ≈ 52 weeks). Work out how many cm that is and mark it.
5. Colour the part of the strip when the frog lives in water and the part when it can live on land.
6. Discuss: the NHM says cold water can delay metamorphosis by months. How would you plan a fair test of whether temperature changes how fast tadpoles develop? (Plan only: do not collect tadpoles.)

Event	Weeks after spawn	Distance on strip (cm)
Spawn laid
Tadpoles hatch
Legs begin
Ready to breed (about 2 years)

Questions

1. Explain the difference between complete and incomplete metamorphosis. Give an example of each.

2. Using your timeline, about what fraction of the time up to breeding is the frog a tadpole?

3. Plan a fair test: which variable would you change, and which would you keep the same, to test whether temperature affects tadpole development?

4. A chick's heart starts beating after about 2 days. How many days later does it hatch on day 21?

Sources for every fact on this sheet: echoesof.science/school/animal-life-cycles/sources/

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