The Colonisation of Ants

How a fungus infects ants and manipulates their behaviour to propagate itself

Symbiosis between ants and fungi has been well documented and long studied, yet it remains a fascinating field of study. Some species of ants actively cultivate fungus much like crops for their use, but only recently have cases come to light where it is the fungus that literally cultivates ants to its end. The cases were first documented in 2009, and have since then been found in rainforests ranging from Asia to South America. The parasitic fungi in each come from the same family Cordyceps; in fact, a chemical derived from the family has now found use in modern medicine as ciclosporin, ensuring that the body of organ transplant patients does not reject new tissue.

Now a detailed study of the process has been published and shows that once ‘tropical carpenter ants living high up in the rainforest canopy are infected by a parasitic fungus (Ophiocordyceps unilateralis), the behaviour of the ants is dramatically changed. They become erratic and zombie-like, and are manipulated by the fungus into dying at a spot that provides optimal conditions for fungal reproduction.’

‘The growing fungus fills the ant’s body and head causing muscles to atrophy and forcing muscle fibres apart. The fungus also affects the ant’s central nervous system and while normal worker ants rarely left the trail, zombie ants walked in a random manner, unable to find their way home. The ants also suffered convulsions which caused them to fall to the ground. Once on the ground the ants were unable to find their way back to the canopy and remained at a lower, leafy, ‘understory’ which, at about 25 cm above the soil was cooler and moister than the canopy, provided ideal conditions for the fungus to thrive,’ reports the study.

‘At noon the fungus synchronised ant behaviour, forcing infected ants to bite the main vein on the underside of a leaf. The multiplying fungal cells in the ant’s head cause fibres within the muscles that open and close the ant’s mandibles to become detached. This results in ‘lock jaw’ which means that an infected ant is unable to release the leaf even after death. A few days later the fungus generates a fruiting body from the ant’s head which releases spores to be picked up by another wandering ant.’

About The Author

Hartosh Singh Bal

Hartosh Singh Bal turned from the difficulty of doing mathematics to the ease of writing on politics. Unlike mathematics all this requires is being less wrong than most others who dwell on the subject.