Parasitism of any kind is fascinating, and is often horrific.

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.