Wasp Gall

It seems like there is no limit to how complex parasitic relationships can become in the natural world. There are some great examples of mutually beneficial relationships (think of the shark and lamprey cruising the seas together) but this wasp gall is certainly not one of them. In this case the arrangement is between a female wasp and a wild rose plant. It is not a happy marriage. The closest human corollary would be rape.
Here's how it works: A female wasp uses her sharp ovipositor (a surprisingly long tube that deposits her eggs) to stab into the stem of the plant. Once the eggs are laid she flies away with no additional parenting duties to perform. Then it gets a little crazy. Instead of simply providing a safe home for the eggs to hatch, her egg packet actually contains a chemical payload that subverts the plant's survival mechanisms. It tricks the plant into diverting it's resources to producing a gall which functions as a home for the larvae as well as a nourishment node. This is not in the rose's best interests at all. Once a gall is produced it takes a disproportionate amount of resources from the plant.
But it gets better. Not only are some animals capable of making completely unrelated species rear their young, but other parasites are adept at using existing galls to provide their young with comfort and ease as well. According to Kaufman's Field Guide to Insects of North America (an amazing resource) when galls are reared in the lab naturalists often find that more than one species of insect will emerge. Consider: larvae eating stolen plant resources only to be eaten in turn by some other insect larvae only to be bird food upon leaving the gall but the bird gets parasites from contact with the gall, etc, etc.
Remember that song from The Lion King The Circle of Life? This is what Elton John should have been singing about; parasites on parasites on parasites. A daisy chain of complex fuckings-over, where even evolving totally effective chemical simulacra to give your young a chance doesn't guarantee success. Make that into a clever ballad and try to sell a soundtrack.