THERE are zombie ants droning and stumbling around Thailand, convulsing and falling over before succumbing to a painful death with a leaf permanently clenched between their jaws.

Scientists at Penn State University have discovered a parasitic fungus is dramatically changing the behaviour of tropical carpenter ants.

The fungus — Ophiocordyceps unilateralis — literally takes over the ant’s brain, filling their head and body with the deadly bacteria until their muscles atrophy, tearing muscle fibres apart.

Unaffected carpenter ants usually walk in a trail, but the fungus attacks the ant’s central nervous system, making it stray from the path and take random routes back to base, unable to find its way home.

The carpenter ants — which usually dwell a top the high canopies of forest regions — then suffer convulsions and fall to the “leafy understory” of the forest, where cooler, moister conditions than the canopy provide an ideal atmosphere in which the fungus can thrive.

And then at high noon — the ideal time of day for a dramatic ending — the “death bite” occurs.

The phenomenon was discovered in four different species of fungus affecting ants in the Brazilian rainforest back in March, but further study by the Penn State team has unlocked the mystery behind the suicidal process.

The fungus takes control of the ant’s motor abilities, forcing it to bite into the main vein in the underside of a leaf and killing it — but not before giving it a permanent case of lockjaw .

The multiplying fungus cells in the ant’s head cause fibres within the muscles responsible for opening and closing the ant’s mandibles to become detached.

It results in a lock jaw which remains even after the ant is dead, meaning that the leaf remains within the clenched jaws of the insect forever.

A few days later the fungus generates a fruiting body out of the ant’s head which releases viral spores that flow within the atmosphere, waiting to be picked up by another wandering ant.



David Hughes, from Penn State University said: "The fungus attacks the ants on two fronts. Firstly by using the ant as a walking food source, and secondly by damaging muscle and the ant's central nervous system, resulting in zombie walking and the death bite, which place the ant in the cool damp understorey.

"Together these provide the perfect environment for fungal growth and reproduction.

"This behaviour of infected ants is essentially an extended phenotype of the fungus (fungal behaviour through the ant's body) as non-infected ants never behave in this way."

