Wasps, like all insects, are covered by a rigid outer casing and must shed this layer to grow. This process of shedding the exoskeleton is called ecdysis, or molting. Wasps do molt, but this action is confined exclusively to their immature, larval stages.
The Biological Necessity of Molting
The need for molting stems directly from the wasp’s physical structure, specifically its exoskeleton. This external skeleton is composed largely of chitin and provides structural support, protection for internal organs, and an anchor point for muscle attachment. For terrestrial insects, the exoskeleton also contains a waxy layer that prevents water loss.
The rigidity of this external shell limits growth. Once the exoskeleton hardens, it cannot expand to accommodate an increase in body mass. As the larval body grows within this fixed casing, the space becomes restrictive. The wasp must periodically shed its entire external structure to allow for a rapid increase in size before the newly formed layer hardens.
Where Molting Occurs in the Wasp Life Cycle
Molting is a characteristic of the larval stage, the second of the four stages in the wasp’s complete metamorphosis (egg, larva, pupa, and adult). The larval phase involves intense feeding and rapid growth, necessitating multiple molts. The period between each successful molt is known as an instar.
Most common wasp species, such as yellowjackets and paper wasps, pass through four to five instars. The process begins hormonally, signaling the larva to separate its inner tissues from the old cuticle, a process called apolysis. The larva then secretes a new, soft exoskeleton underneath the old one. Simultaneously, it releases enzymes to digest and reabsorb the inner layers of the discarded shell.
During ecdysis, the larva forces its body to swell, often by swallowing air, causing the old cuticle to split along predetermined lines. The soft larva then wriggles free from the old skin, or exuvia. Once emerged, the new exoskeleton is pliable, allowing for rapid expansion in size before it hardens.
The Final Transformation
The molting phase concludes when the larva reaches its maximum size, transitioning into the pupal stage. The larva spins a silken cap over its cell and ceases to feed, preparing for the internal reorganization known as metamorphosis. The pupa is a non-feeding, inactive stage, and since there is no growth, there is no further need for ecdysis.
Inside the pupal casing, larval tissues are broken down and reassembled into the structures of the adult wasp, including wings, legs, and antennae. This internal change is the final step before the adult emerges. Once the adult wasp breaks free from the pupal case, it has reached its final, fixed size and will not molt again.