Why do parasitic wasps lay eggs inside other insects?

Many parasitic wasps have evolved a reproductive strategy in which their offspring develop inside or on other arthropods. The female uses precise egg-laying behavior to target a suitable host, often a caterpillar, beetle larva or spider, depending on the species. Once the egg hatches, the larva feeds on the host and eventually kills it, which sounds gruesome but is a highly successful life history. This relationship is important in ecology and agriculture because many parasitic wasps naturally control pest populations. The group is enormously diverse, with tens of thousands of described species and likely many more unknown.