Cordyceps Parasitic Fungus

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.