Carl Zimmer in his blog, The Loom (via Pharyngula):
Thanks to PZ Myers for calling attention to this superb video of Corydceps, a parasitic fungus that drives its insect host up a plant before growing a spike out of its head. Leave it to David Attenborough, master of the nature documentary, to bring the beauty of this parasite to video. I’ve seen photographs of Cordyceps before, but I never knew it made such a graceful entrance.
What’s particularly cool about Cordyceps is that it is not alone. Other parasites drive their hosts to bizarre heights. Another fungus, called Entomophthora muscae, drives houseflies and other insects upwards, climbing screen doors in some cases, before springing out of its host’s body.
In the case of Entomophthora and Cordyceps, hosts go up so that parasites can come back down again–specifically, down on potential insect hosts living on the ground. But other parasites have another direction in mind. The lancet fluke drives its insect hosts up to the tops of plants so that grazing mammals may eat them. Only in the gut of a cow or some other grazer can the flukes mature and reproduce. These creatures are like the birds, bats, and pterosaurs of the parasitic world, hitting on the same brilliant solution again and again.
(Here’s the place where I write about these parasites in my book, Parasite Rex.)