>> DAVID ATTENBOROUGH: Incredibly, 80 percent of all insects

live in jungles.

Few are more successful
than the ants.

There can be eight million
individuals in a single hectare.

But jungle ants don't
have it all their own way.

These bullet ants are showing
some worrying symptoms.

Spores from a parasitic
fungus called cordyceps have

infiltrated their
bodies and their minds.

Its infected brain
directs this ant upwards,

then utterly disorientated, it
grips a stem with its mandibles.

Those afflicted, if they're
discovered by the workers,

are quickly taken away and
dumped far away from the colony.

It seems extreme, but
this is the reason why.

Like something out of science
fiction,

the fruiting body of the cordyceps erupts
from the ant's head.

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It can take three weeks to grow.

And when finished, the deadly
spores will burst from its tip.

Then, any ant in the
vicinity will be

in serious risk of death.

The fungus is so virulent,

it can wipe out whole
colonies of ants.

And it's not just ants that
fall victim to this killer.

There are literally thousands

of different types
of cordyceps fungi.

And remarkably, each
specializes on just one species.

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But these attacks do
have a positive effect

on the jungle's diversity, since parasites

like these stop any one group of
animal getting the upper hand.

The more numerous a species becomes,

the more likely it'll be attacked by its nemesis,

a cordyceps fungus.