Nymph, in biology, an immature insect. The young of more than half of the orders of winged insects are called by this name. Insects of these primitive orders develop by incomplete metamorphosis—from the egg through the nymph stage to the adult form. When a nymph hatches from the egg, it resembles the adult of its species, except in size. However, it has no wings and is sexually immature. Since its skin does not stretch, a nymph must molt (shed its skin) in order to grow. Most nymphs molt five or six times before they become adults. Insects having the nymph stage include grasshoppers, cockroaches, cicadas, termites, and true bugs.

The nymphs of dragonflies and mayflies have developed special structures for breathing under water. These water nymphs are called naiads.

and illustration Incomplete Metamorphosis.