Life Cycle
Like other fungi pathogenic to insects in the Ophiocordyceps genus, O. unilateralis targets a specific host species, the Camponotus leonardi ant. However the fungus may parasitize other closely related species of ants with lesser degrees of host manipulation and reproductive success.
The fungus's spores enter the body of the insect likely through the cuticle by enzymatic activity, where they begin to consume the non-vital soft tissues. Yeast stages of the fungus spread in the ant's body and presumably produce compounds that affect the ant's brain and change its behaviour by unknown mechanisms. The insect climbs up the stem of a plant and uses its mandibles to secure itself to a leaf vein, with abnormal force, leaving dumbbell-shaped marks on it. A search through plant fossil databases revealed similar marks on a fossil leaf from the Messel pit which is 48 million years old.
The fungus then kills the ant, and continues to grow as its hyphae invade more soft tissues and structurally fortify the ant's exoskeleton. More mycelia then sprout out of the ant, and securely anchor it to the plant substrate while secreting antimicrobials to ward off competition. When the fungus is ready to reproduce, its fruiting bodies grow from the ant's head and rupture, releasing the spores. This process takes 4 to 10 days.
The changes in the behavior of the infected ants are very specific, giving rise to the popular term "zombie ants", and tuned for the benefit of the fungus. The ants suffer from convulsions causing them to fall to the ground and preventing them from finding their way back to their canopy. The ants generally clamp to a leaf's vein about 25 cm above the ground, on the northern side of the plant, in an environment with 94-95% humidity and temperatures between 20 and 30 °C. According to David Hughes, "You can find whole graveyards with 20 or 30 ants in a square metre. This fungus has been known to wipe out whole colonies of ants. Each time, they are on leaves that are a particular height off the ground and they have bitten into the main vein before dying". When the dead ants are moved to other places and positions, further vegetative growth and sporulation either fails to occur or results in undersized and abnormal reproductive structures.
Read more about this topic: Ophiocordyceps Unilateralis
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