A35 Repair and healing

Topic

The insect has a limited capacity to repair its own exoskeleton when it is damaged between molts: as soon as a wound occurs in the exoskeleton, hemocytes—immune cells circulating through the insect's body—rush to the site and seal the breach with hemolymph that coagulates over it, acting as an initial emergency response.

Once the coagulated hemolymph has sealed the wound, epidermal cells beneath the area begin depositing new cuticle over the sealed gap. The speed at which this cuticle deposition proceeds depends on two simultaneous factors: the concentration of ecdysone—the same molting hormone, though in this instance released locally at the wound site—and the size of the wound area requiring coverage; the greater either of these values ​​is, the faster the deposition of new cuticle progresses.

The insect does not simply wait for cuticle deposition to proceed on its own; it also employs active closure via muscle contraction, drawing the wound edges together and thereby directly reducing the surface area that the epidermal cells must cover with new cuticle.

Simultaneously, the hemolymph components required for wound repair do not reach the entire injured area all at once; instead, they diffuse toward it in a gradual pattern—more concentrated near the wound site and decreasing toward the edges of the healthy tissue—consistent with Fick's diffusion equation for this type of advancing front. Despite this entire process, the repair cuticle that eventually covers the wound rarely matches the quality of the original exoskeleton cuticle; its toughness—that is, its ability to resist crack propagation—typically ranges from thirty to seventy percent of the original value, and this disparity leaves a scar that is structurally more fragile than the rest of the exoskeleton.

The success of this repair—specifically, the efficiency with which the insect managed to seal, cover, and reinforce the wound—determines whether it can resume normal flight and locomotion despite the weaker scar, or if it must make do with reduced capabilities until the next molt. Only during that subsequent molt does the insect regain a complete, renewed exoskeleton, free of any scars accumulated since its last molt.

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