Washington, Aug 12 - A fungal parasite coerces ants into dying in just the right spot -- one that is ideal for the fungus to grow and reproduce, a new study has found.

The study, led by David P. Hughes of Harvard University, shows just how precisely the fungus manipulates the behaviour of its hapless hosts.

When a carpenter ant is infected by a fungus known as Ophiocordyceps unilateralis, the victim remains alive for a short time. The fungus, however, is firmly in the driver's seat.

It compels the ant to climb from its nest high in the forest canopy down into small plants and saplings in the understorey vegetation.

The ant then climbs out onto the underside of a low-hanging leaf where it clamps down with its mandibles just before it dies. There it remains, stuck fast for weeks.

After the ant dies, the fungus continues to grow inside the body. After a few days, a stroma -- the fungus's fruiting body -- sprouts from the back of the ant's head.

After a week or two, the stroma starts raining down spores to the forest floor below. Each spore has the potential to infect another unfortunate passerby.

Scientists have known for over 100 years about this parasite's ghastly ability to turn unsuspecting ants into zombies.