What is the term for the empty exoskeleton left behind when an insect molts?

The term for the empty exoskeleton left behind when an insect molts is indeed exuvium. This term specifically refers to the cast-off skin or exoskeleton that occurs in various arthropods, including insects, as they grow and mature. During the molting process, an insect sheds its old exoskeleton to allow for growth, and the exuvium represents the remnants of this old structure.

Chitin is a structural polysaccharide that makes up the exoskeleton itself, but it does not refer to the shed exoskeleton. The cuticle is the outer protective layer of the exoskeleton that includes chitin, but it encompasses more than just the exuvium; it is a broader term describing the entire layer. Larva refers to a developmental stage of certain insects, not to the discarded exoskeleton.