Tachinids are a family of flies that use other insects to complete their life cycles. This means that large caterpillars can be the host for one to two dozen fly larvae. In this case, a Manduca sexta moth larva (tobacco hornworm/carolina sphinx) becomes an unwilling host to Winthemia manducae1 flies. To quote the source: “(This fly) is often seen near last stage hornworm larvae. Eggs of this species hatch, and the maggots bore into the hornworm. The hornworm is killed while in the soil during the pupal stage, before it can transform into an adult and initiate a new generation.