Many insects are parasitized by other insects- in fact this is a major way the number of bugs is kept in check. Called parasitoids, their invasion of a host results in its death. A particularly interesting example is the wasp Cotesia congregata. A female wasp lays many eggs into the body of a caterpillar like the tobacco hornworm, Manduca sexta. Eggs hatch and the developing larvae grow as they feed on its hemolymph (blood). Vital tissues are not damaged, so the caterpillar is not killed. Instead, when the larvae reach a late stage of development, they bore through the caterpillar wall and form the white pupal cases on the outside of the body. Adult wasp will emerge from these pupae. The cool part is that the parasitoid affects the caterpillar immune system in ways that makes the exit holes made by the emerging larvae temporarily numb. This means the infected insect will not feel them and lash out to destroy the attached pupae. Another big effect is that the invader causes the caterpillar to stop eating- it eventually starves to death! By keeping the host whole and alive our parasitoid assures it can complete its development.
To learn more, see Adamo et al. (2016). Journal of Experimental Biology, 219:3750-
Photo Credit: RJ Reynold Tobacco Company, bugwood.org