Wasps make caterpillars into zombie guards

A tiny wasp, barely visible to the naked eye, injects its eggs into a caterpillar. As those eggs hatch, the larvae begin to feed on the caterpillar's insides. The caterpillar doesn't just die, though. Instead, it becomes a loyal, zombie-like protector for the wasp's cocoons, lashing out at predators even after its own body has been devoured.

This happens when parasitic braconid wasps take over. After the eggs are implanted, the larvae develop inside the host, feeding on non-vital tissues. They keep the caterpillar's nervous system and the muscles used for movement and defense working. Before the larvae emerge to spin cocoons outside the caterpillar's body, they trigger a shift in the caterpillar's behavior that turns it into a defender.

This manipulation transforms the caterpillar. Instead of fleeing or dying, it guards the wasp cocoons with its life, twitching and lashing out at anything that approaches. Researchers believe the process interferes with the caterpillar's normal hormonal balance, suppressing its feeding instincts and rewiring its aggression. A few larvae typically remain behind in the caterpillar's body and do not pupate, though the exact reason for this is still being studied by scientists.

Once the wasp pupae are safe and ready to hatch, the usefulness of their living shield expires. The remaining wasp larvae or the continued effects of the biological changes eventually lead to the caterpillar's death. It's a brutal strategy that ensures the next generation of wasps survives at the cost of the caterpillar's body and mind.