Grim details of how a fungus turns forest ants into “zombies” to control their behaviour before killing them have been uncovered by scientists.

Like an alien invader from Doctor Who, the parasitic fungus takes over the brains and bodies of tropical carpenter ants.

The insects, which normally live high in the forest canopy, stagger and fall to the ground. Attempting to climb back up, they get no further than an “understorey” spot with ideal conditions for fungal reproduction.

There they die, their mandibles (crushing organs in the mouth) locked in a “death grip” on leaves about 25 centimetres above the ground where the air is cool and moist. A few days later the fungus erupts from the ant’s head and releases spores to be picked up by other victims.

Scientists investigating infected carpenter ants in Thailand discovered that the fungus fills the body and heads of the insects, causing muscles to waste away and forcing the muscle fibres apart.

It also gets into the ant’s central nervous system, producing “zombies” which walk randomly and suffer convulsions, causing them to tumble out of the trees.

Fungal cells multiplying in the ant’s head detach the mandible muscles, locking the jaws.

David Hughes, from Pennsylvania State University, who led the study published in the online journal BMC Ecology, 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 understory.

“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 this way.”