Many caterpillars are covered with hair or spines like stinging nettles. They irritate the skin and evoke inflammations. They also keep parasites from laying their eggs on the caterpillars.

Some caterpillars store toxins from the plants they eat, making them bad-tasting, inedible and poisonous. Predators are warned by the bright colors. Other caterpillars have eye patterns seeming to scare predators.
The caterpillars of some species of the Tiger-Moths emit a drop of yellow blood behind their head. The color and smell of the drop scare away aggressors.
Caterpillars of Swallowtails can put out a bright, smelly fork. Besides scaring predators, this fork is used to emit essential oils from food plants.
When you poke a Swallowtail caterpillar, it emits horribly-smelling butyric acid. Some other caterpillars behave in a similar way.
Caterpillars of Pusses can spray a poison up to 10 inches (20 cm) that can make birds blind.
Several species rope down on silk threads to escape from ants.
Pretending to be dead or moving suddenly are other methods of fooling and surprising predators.

Pupae mainly protect with camouflage and cocoons or web of silk surrounding them.

Butterflies and moths are covered with detachable scales that enable them to slip away when they are in the web of a spider or held in grasp of a predator.

Hearing signals of a bat the Tiger moth drops like a stone from its flight while it makes high-pitched noises to confuse the bat. This makes it easier to escape.
Above all, the remarkable ability of increase ensures the survival of butterflies and moths.