Oh, the Horror!

"This image may look like something dreamed up for a surreal horror movie, but it's a real horror for the tarantula in question. This unfortunate arachnid is infected with Cordyceps, a parasitic fungus that replaces its host's tissue with its own.

Cordyceps fungi invades its hosts (mainly arthropods), and its mycelium eventually replaces the host's tissue. Once the arthropod is dead, cylindrical or branching growths emerge from the creature's dead body. Some species also have mind-control capabilities, convincing the host to travel to a place where the fungus will find optimal growth conditions before the host dies."