I've found a bunch of awesome videos on YouTube demonstrating a fascinating aspect of nature: parasites that take over part of the host's brain, resulting in a kind of behavior that will further the parasite's life cycle.
First, a parasite, having outgrown its cricket host, convinces the cricket to drown itself. Thus, the parasite has a chance to swim away (sorry, no sound on this one):
It's amazing, the kind of stuff that evolution makes possible. If you're having trouble thinking of how something like this could evolve, think of it this way. (This is just a hypothetical, of course, and an over-simplified one at that, so forgive me. :-P) That parasitic worm's ancestor also needed to grow in a cricket and seek out water. Some crickets were bound to drown just by accident, so that was just fine: few of the parasites would make it from cricket to water, but enough would to continue the species. Now, imagine a random mutation that made some of that worm's offspring have the slightest effect on their hosts, so those hosts tended to be slightly more attracted to water. This small effect couldn't guarantee that the cricket would drown, but over a large population, a slightly greater proportion of these mutated worms would reach the water compared to the non-mutated ones. Thus, the mutants pass on their genes, and the water-seeking allele increases in frequency. Now, just repeat the process. More water-directing mutations stack upon the first, gradually increasing the effect until the parasite practically has total control over the water-seeking portion of the cricket's little brain.
Next (and my personal freak-out favorite), this poor snail has worms. I bet he's all the rage at the local discotheque, but I don't know that it would be worth it to have pulsating worms in your freaking brain:
And last but not least, mind-controlling fungi attack insects. The time-lapse growth of the fruiting body (~1:07 to 1:45) is particularly cool, as is the fungus-covered moth:
Speaking of fungi, I've got a post up at my blog Synapostasy talking about a recent study of melanin-containing fungi and radiation. Feel free to check it out! (There's also some stuff in that post about fish and limb development.)