Definition
Metamorphosis is the biological process an insect goes through as it develops from an egg into an adult, and insects use one of two very different strategies to get there. In complete metamorphosis, the insect passes through four distinct stages — egg, larva, pupa, and adult — and the larva looks nothing like the adult it will become. A fly starts as a maggot, a beetle starts as a grub, and a moth or butterfly starts as a caterpillar; each then enters a pupal stage where its body is essentially rebuilt before it emerges as a winged adult. Flies, beetles, moths, ants, bees, and wasps all develop this way.
In incomplete metamorphosis (also called simple or gradual metamorphosis), there's no pupal stage at all. The insect goes through just three stages — egg, nymph, and adult — and the nymph already looks like a smaller, wingless version of the adult from the moment it hatches. It grows larger and more adult-like with each molt, gradually developing wings and reproductive organs over a series of instars until it reaches full adult form. Cockroaches, bed bugs, true bugs (like stink bugs and boxelder bugs), grasshoppers, and termites all develop this way.
This distinction is more than academic — it directly shapes how a pest control technician approaches treatment. Because complete metamorphosis hides most of a pest's population in stages (eggs, larvae, or pupae) that don't resemble the adult and may not respond to the same products, effective control often has to account for multiple life stages hitting the site on different timelines. With incomplete metamorphosis, nymphs are usually vulnerable to the same treatments as adults, but their small size can make early infestations easier to overlook.