Parasitic wasps are gross, but fascinating. If I recall correctly there is a parasitic wasp that parasitizes a parasitic wasp that parasitizes a parasitic wasp that parasitizes some kind of caterpillar.
The caterpillar: Often a pest species like the tomato leafminer
Primary parasitoid: Cotesia glomerata
Secondary parasitoid: Lysibia nana and some species from the genus Gelis like agilis
Tertiary parasitoid: Certain species within the Trichogramma or Eulophidae families.I was on a bird walk yesterday morning and one of the participants pointed out a brightly colored black and yellow millipede that had climbed up a tree trunk. What was it doing there? I can't be sure, but that species is subject to attack by a fungus that takes control and makes it climb up tree trunks, walls, fenceposts, etc. so that as it expires it discharges spores well above the ground.
A relevant SMBC: https://www.smbc-comics.com/?id=2331
Parasitic wasp interactions are also where nature is truly vicious. A predator like a big cat will hunt many times over its life. It cannot risk too much in each encounter, so the interactions are to some extent subdued, the prey often escaping. But with parasitic wasps, it may succeed just once in its life. The stakes are as high as they can be, and the wasp can risk all to succeed.
https://en.wikipedia.org/wiki/Arthrophaga_myriapodina
The millipede species: https://en.wikipedia.org/wiki/Apheloria_virginiensis
They're wild. They're born inside the eggs of barklice, and mate there. Males are ~186 micrometer, smaller than some single celled organisms like amoeba!
"Yo Dawg, we heard you like parasites, so we put a parasite INSIDE your parasite INSIDE ..."