Issues with an Exoskeleton
This exoskeleton still restricts growth and needs to be shed periodically, and a new shell created to replace it. Primitive insect forms like bristle tails and springtails do not change their shape significantly with successive changes of the exoskeleton, but this does permit them to increase their size. The early winged- insect forms (cockroaches, cicadas, crickets and dragonflies) similarly moult without significant changes to the body shape with the exception of acquiring wings in the final moult (although damsel flies take two moults to perfect their wing structure. Even when insects adopt significantly different environments for their early and later lives, their body structure is recognizably similar.