A parasite is a living thing that must live on or in another living thing to survive. Some parasites you may have encountered before are animals like head lice, which live on human scalps and feed on blood. Have you ever been bitten by a leech? They’re parasites too! Mites and gut worms are other common parasites of humans, and there are even plants that are parasites of other plants! Parasites tend to keep their host (the living thing they are feeding from) alive for a long time.
A parasitoid, unlike a parasite, often kills their host as part of their lifecycle. When a parasitoid wasp lays her eggs inside the host, the eggs hatch and the baby wasps (larvae) eat the host slowly from the inside, being careful not to kill the host too quickly. When they have grown enough, the larvae eat their way out of the host, which normally kills it, and form cocoons on the body of the host. The larvae undergo metamorphosis in their cocoon and emerge as adult wasps. Watch the video below to see it in action.
An endoparasitoid lives inside their host, whilst an ectoparasitoid lives on the outside of their host, such as on the hair or skin. The particular group of wasps we are studying are endoparasitoids that live inside caterpillars of butterflies or moths. They are important as natural enemies of caterpillars, keeping their populations in balance, and also as biological control agents. Biological control agents are animals (or other organisms like bacteria, viruses or plants) that are used in agriculture to reduce pest numbers. Some parasitoid wasps are used in crops to keep pest caterpillars from building up large population numbers where they can badly damage the plants.