Ophiocordyceps unilateralis

Ophiocordyceps unilateralis has become synonymous with the 'zombie ant' phenomenon, though it actually represents a species complex with many host-specific variants. When spores land on a carpenter ant, the fungus penetrates the exoskeleton and grows inside the ant's body, eventually taking control of its behavior. The infected ant leaves its colony, climbs vegetation, and bites down on a leaf or twig at a specific height and orientation optimized for fungal spore dispersal. Then it dies, and the fungus erupts from its head.

The precision of behavioral control is extraordinary. Infected ants bite leaf veins on the north side of plants, at specific heights above the forest floor, during midday. This positioning places the dying ant in conditions—humidity, temperature, height—optimal for fungal spore development and dispersal. The fungus has evolved to manipulate ant neurobiology so precisely that ant behavior becomes an extension of fungal reproduction strategy. The ant is a vehicle; its behavior is the fungus's tool.

Recent research reveals the fungus doesn't directly invade the ant's brain. Instead, fungal cells form networks around muscle fibers, controlling movement through the body's periphery rather than the central nervous system. The brain remains relatively uninfected even as the ant's behavior transforms completely. This peripheral control mechanism suggests the fungus hijacks the motor system directly, bypassing higher neural processing. The zombie ant represents the most sophisticated known example of extended phenotype—an organism controlling another organism's behavior as if it were its own body.