Download 5.10C Key Concepts

Key Concept 1: Complete metamorphosis in insects involves four
distinct differences in life stages, including egg, larva, pupa, and adult.
Metamorphosis means change. About 88% of all insects go through complete
metamorphosis, which has four stages:
1) Egg - A female insects lays eggs.
2) Larva Larvae hatch from soft eggs, but do not look like adult insects. They
usually have a worm-like shape. Some insects have special names for the larval
state: caterpillars (butterfly and moth larva), maggots (fly larva), and grubs
(beetle larva). Larva molt (shed) their skin several times and eat constantly as
they grow larger.
3) Pupa - Larvae encase their bodies inside a pupa to undergo the final change
into their adult form. The hard green pupa of a butterfly is called a chrysalis. A
moth pupa is covered in silk strands and is called a cocoon. Larvae don’t eat
while they’re inside their cocoons. Their bodies develop into an adult shape with
wings, legs, internal organs, etc. This change takes anywhere from 4 days to
many months.
4) Adult - Inside the pupa, the larvae change into the adult form of the insect.
After a period of time, the adult breaks out of the pupa, complete with wings.
Key Concept 2: Incomplete metamorphosis in insects involves three
life stages, including egg, nymph, and adult.
About 12% of all insects go through incomplete metamorphosis, which lacks
the larval (caterpillar) and pupa (cocoon) stages. Instead, the insect merely
emerges from the egg in a small adult form without wings and molts several
times before eventually growing wings and becoming an adult. Incomplete
metamorphosis has three stages:
1) Egg - A female insect lays eggs. These eggs are often covered by an egg
case, which protects the eggs and holds them together.
2) Nymph - The eggs hatch into nymphs. Nymphs look like small adults, but
usually don’t have wings. Insect nymphs eat the same food that the adult insect
eats. Nymphs shed or molt their exoskeletons (outer casings made up of a hard
substance called chitin), and replace them with larger ones several times as they
grow. Most nymphs molt four to eight times.
3) Adult - The insects stop molting when they reach their adult size. By this time,
they have also grown wings.
Key Concept 3: Butterflies and beetles undergo complete
metamorphosis, while grasshoppers and walking sticks undergo
incomplete metamorphosis.
Students will explore and sort insects into two categories based on
pictures of developmental stage. Alert students to look for two stages that
are clues to “complete metamorphosis”: the larva and the pupa stage.
Without those two stages, the insect belongs to the “incomplete
metamorphosis” group. Also, students can look for a miniature adult
insect without wings to find the “nymph” stage, which is the clue for
sorting pictures into the “incomplete metamorphosis” group.