Life Cycles

Jamie Sipe

Simple Life Cycles

Most animals including fish, mammals, reptiles and birds have very simple life cycles:

  • they are born (either alive from their mother or hatched from eggs)
  • they grow up

These animals have three stages -- before birth, young and adult. The young are typically similar to the parent, just smaller. The young slowly "grow" to become adults.

Amphibian's Life Cycle

Amphibians, like frogs and newts, have a slightly more complicated life cycle. They undergo a metamorphosis (a big change):

  • they are born (either alive from their mother or hatched from eggs)
  • they spend their childhood under water, breathing with gills
  • they grow into adults and move to the land, breathing with lungs

Metamorphosis

What is Metamorphosis?

Metamorphosis is a process some animals go through to become adults. It is a series of physical changes. Metamorphosis is especially common in insects. Genes and chemicals called hormones control the process.

Complete Metamorphosis

Insects

These insects have four stages in their life cycle:

  • egg: unborn stage.
  • larva: young stage -- this is when most of the feeding is done.
    (they usually look like worms)
  • pupa: inactive (no feeding) stage between larva and adult stages.
    (usually well camouflaged)
  • adult: final, breeding stage.
    (they usually grow wings)

Incomplete Metamorphosis

Insects

About 10% of insects go through an incomplete metamorphosis. They do not have a pupal form -- these include dragonflies, grasshoppers and cockroaches.

These insects have three stages in their life cycle:

  • egg: unborn stage.
  • nymph: young stage -- this is when most of the feeding is done.
  • adult: final, breeding stage - including wings.