Definition
Molting, also called ecdysis, is the process an insect or other arthropod (like a spider or a tick) goes through to shed its old exoskeleton and grow. Unlike a human's skin, an insect's exoskeleton is a hard, protective outer shell that can't expand as the animal inside it grows. So the insect grows a new, slightly larger and initially soft exoskeleton underneath the old one, splits and wriggles free of the old shell, and then has to wait for the new one to harden before it can move around normally again. This cycle repeats multiple times over an insect's life, with each stage between molts called an instar.
This is exactly why homeowners sometimes find what looks like a dead, hollow insect — still fully formed, legs and antennae intact — only to realize on closer look that it's weightless and papery. That's not a dead bug at all; it's a cast exoskeleton, sometimes called an "exuviae," left behind after the living insect molted and moved on. This is extremely common with cockroaches, and finding a cluster of shed skins in a cabinet or behind an appliance is actually a useful clue for a pest control technician, since it's a strong sign of an active, reproducing population rather than a single wandering insect.
- Cockroach nymphs molt roughly six to eight times before reaching adulthood, shedding a skin at each stage.
- Bed bugs must feed on blood before each molt, which is part of why interrupting their feeding access is a key part of treatment.
- Spiders and ticks molt too, since they're arthropods with an exoskeleton, even though they aren't insects.