Glyptapanteles Wasp

After the wasp impregnates a caterpillar with its eggs, the behavior of the host caterpillar begins to radically change. First the caterpillar stops moving. Then, after the eggs hatch and the pupae crawl out of the caterpillar's body, the caterpillar involuntarily protects the pupae from attack by thrashing wildly in the presence of predators. Although the exact biochemistry used by the wasp larvae to transform an otherwise benign caterpillar into a Manchurian Candidate-like slave remains unknown, the researchers did show that the presence of a zombie caterpillar guardian performing "violent head-swings" significantly increased the survivability of the pupae. My character will impregnate grief into its host and just like the Glyptapanteles wasp, it controls the mind of the host as it goes on this personal journey.