By definition, a parasitoid is an organism that lives on or in a host organism and ultimately kills the host. The pictured Pelecinid Wasp is a parasitoid. Its host is the grub, or larval stage, of June Bug beetles. The female Pelecinid Wasp uses its long abdomen to probe into the soil until it locates a June Bug grub and then it lays an egg on the grub. When the egg hatches, the wasp larva burrows into and feeds on the grub, eventually causing its death.
A parasite is much like a parasitoid, deriving nutrients from a host, but, unlike a parasitoid, a parasite does not usually kill its host. Often parasites are much smaller than their host, and frequently live in or on their host for an extended period of time. In this photograph, a parasitoid, the Pelecinid Wasp, is host to reddish parasitic mites (located on its thorax).