As if Army Ants weren't bad enough

[Ron Caliburn]

Now we have to worry about Zombie Ants

It could be the plot from a straight-to-DVD horror movie - a fungus slowly turns host creatures into zombies before killing them off.

But such parasites are a reality and are destroying colonies of ants in the Amazonian rainforest.

The fungus latches on to carpenter ants as they cross the forest floor before returning to their nests high in the canopy.

The fungus then grows inside the ants, taking over their bodies and releasing chemicals to alter their behaviour.

Some of the insects wander off to find fresh leaves, while others fall from the tree tops on to leaves nearer the ground.

It is all part of the mechanism used by the fungus to ensure its spores are spread as far and wide as possible.

The final stage of the parasitic death sentence is particularly grim.

The fungus will 'guide' the infected ant to a leaf and lock their mandibles in a 'death grip' around the central vein, immobilising themselves and locking the fungus in position.

Once an ant has died, the fungus sprouts from its head and produces a pod of spores, which are dropped at night on to the forest floor.

The fungus cannot grow high up in the canopy or on the forest floor, but infected ants often die on leaves midway between the two, where the humidity and temperature suit the fungus.

On a recent trip to the rainforest four new species in the genus Ophiocordyceps were found by David Hughes, from Penn State University, and Harry Evans, from the Centre for Agriculture and Biosciences International in Surrey.

Their results have been published in the online journal PLoS ONE.

'It's a fabulously complex organism,' Dr Hughes told the Guardian. 'There is a beauty to the whole thing, whether it is the chemicals at work that take over the ant, or the spores which try one strategy and then another to find a host on the forest floor.'

Scientists are not clear how the fungus controls the ants, but know that it releases alkaloid chemicals into the insect as it consumes it from the inside.

The four new species all come from the rainforest in south-eastern Brazil, which is the most heavily degraded biodiversity hotspot on the planet. Ninety-two percent of its original coverage is gone.

According to the scientists each of the species is highly specialised on one ant species and has a suite of adaptations and spore types to ensure infection.

The life-cycle of these fungi that infect, manipulate and kill ants before growing spore producing stalks from their heads is remarkably complicated.

The present work establishes the identification tools to move forward and ask how forest fragmentation affects such disease dynamics.

Last summer the oldest evidence of such parasites was found on the leaves of plants that grew in Messel, Germany, 48million years ago.

The scientists have also found six species of the fungus in the rainforests surrounding Cairns, Australia.

[neftosis]

Yes I saw some footage of this, it's pretty gruesome. I hate seeing any living thing die, but seeing those ants was just terrible.

[GhostSpider]

Zombie ants?!!

For once, I have no words.

Although, isn't killing zombies kind of like pest control anyway. This just makes it official.

[Slendy Hunter]

One thing I've come to realize over the years: Mother Nature ain't exactly the kind ol' hag she's made out to be. This just goes to further prove it.

Anyone got any anti-fungal spray, and willin' to drive to South America with me?

[Ron Caliburn]

It's getting weirder

New gruesome details have emerged explaining how a parasitic fungus manipulates an unfortunate ant, filling its head with fungal cells and changing its muscles so the ant can grab a leaf in a death grip just when and where the fungus wants it.

Research in a Thai rain forest has shown the fungi, a species of Ophiocordyceps, forces an infected ant to wander drunkenly over the forest's low leaves before clamping its jaws around the main vein on the underside of a leaf in an ant zombie graveyard. [Mind Control: Gallery of Zombie Ants]

By watching 16 infected ants bite down, the researchers found that their last bites took place around noon, indicating they are synchronized to either the sun or a related cue, like temperature or humidity.

"Synchronized arrival of zombie ants at the graveyards is a remarkable phenomenon. It adds a layer of complexity on what is already an impressive feat," wrote David Hughes, a study researcher from Pennsylvania State University, in an email to LiveScience. "However, although ants bite at noon they don't in fact die until sunset. Likely this strategy ensures (the fungus) has a long cool night ahead of it during which time it can literally burst out of the ant's head to begin the growth of the spore-releasing stalk"

The bizarre sequence that leads up to the ant's death is completely out of step with its normal behavior and appears to be a way for the fungus to get itself to the perfect spot to spread its spores, according to the researchers.

The ants, a species called Camponotus leonardi, live in the canopies of trees, but come to the ground occasionally, where they contract the fungus. Healthy ants travel on trails unlike infected ones, which zigzag in a drunken walk over low vegetation, sometimes falling and convulsing before taking their final bite.

Hughes and colleagues observed a total of 42 infected ants, some of which they dissected. While holding its death grip, the ant's head was filled with fungal cells and the muscles that operated the ant's mandible, or jaw, was atrophied, they found.

"In the context of biting, it allows the mandibles, we feel, to work in one direction and one direction only," Hughes told LiveScience. "Normally, they open and close, but in this case they can only close."

This keeps the dying ant from losing its grip. The fungus also appears to suck all of the calcium out of the muscles, causing a condition similar to rigor mortis, he said.

Fungi have been observed to manipulate the behavior arthropods as well, including crickets, bees, wasps and perhaps even spiders.

"We are quite confident we could see this and similar phenomenon across a broad range of organisms, because it is such a neat evolutionary trick if you are fungus to use the muscles of an animal to transport you to another environment," he wrote. (Many fungi rely on wind or other means to passively disperse their spores.)

More broadly, many parasites -- be they plant, animal or virus -- can alter the behavior of their hosts.

In the most recent study, published in the journal BMC Ecology, Hughes and colleagues observed and examined healthy and infected ants to compare their movements and reveal the physiological effects of the fungus. In a previous study, published in 2009, they found that the fungus manipulates infected ants to take it to ideal places for it to reproduce in the forest understory. As result the dead ants wound up on leaves on the north-northwestern side of plants approximately 9.8 inches (25 centimeters) above the ground.

[Slendy Hunter]

Now that's just creepy... Hopefully noone gets the idea (and figures out how) to do that sorta thing to people!

[GhostSpider]

I can guarantee you that the moment this study hit the stands, someone started thinking on how to do exactly that. It's human nature.