>> 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.