Hyperparasitism: Parasites that are parasitic to parasites!
The wonderful world of entomology - parasites within parasitoids all over the place! Though parasites are found throughout the natural world, insects have some of the most interesting examples found between (and sometimes within) the families of the order, including many hyperparasites.
At top, you can see the parasitoid (a parasite that generally consumes or intentionally leads to the death of the host - long-term survival within the host is not the goal) burrowing-wasp parasitizing the rhinoceros beetle larva. Once the female burrowing-wasp “smells” out the location of the larva, she burrows down to it and lays an egg on the body. After her egg hatches, it feeds on the larva. When the beetle larva is consumed, the burrowing-wasp pupates, and forms a chrysalis underground. After metamorphosis, it digs its way up and out, and feeds on pollen or nectar while searching for a mate.
But the insect world does not always let one get away with that sort of parasitoid behavior for free! Many members of the Hymenoptera, including the burrowing-wasps, are in turn parasitized by Strepsiptera, formerly known as the “twisted-winged parasites”. This parasitism of parasites (or parasitoids) is known as hyperparasitism, and is mostly found in entomophagous (insect-eating) insects.
As larva, Strepsiptera are free-roaming insects, looking for a host. Once the appropriate host is found, the larvae will enter the insect (using various mechanisms) and take up residence in its abdomen, as can be seen in the image on the bottom-right. Both sexes go through the last instars (moults) of their larval stage within the host. After this stage, there is a vast difference between the females and the males - the males pupate, go through a complete metamorphosis, and emerge from the host as adults (of course, killing the host in the process). The females become neotenous adults (adults capable of reproduction, but with juvenile forms - axolotls are another example), and stay within the host for their entire life. The male mates with them while they’re within the host, and their eggs hatch inside their bodies.
Fun fact: When the Strepsiptera larvae emerge from the host, the brood canal they come out of is generally at the top of the abdomen, just below the head, so the host ends up having babies coming out of its “neck”. This doesn’t kill them, and some hosts end up sustaining three or more broods of its parasite. Cool stuff!
Top: Burrowing-wasp parasitizing rhinoceros beetle. Marvels of Insect Life. Edward Step, 1916.
Bottom Right: Adult male Strepsipteran (Stylos dalii), free of host. British Entomology. John Curtis, 1823-1840.
Bottom Left: Adult female Strepsipteran and adult female Strepsipteran within host. Applied Entomology. H.T. Fernald, 1921.