The morning dew drips slowly outside your window. As the sun rises you wake up, yawn, and stretch your legs. The overtime you had yesterday at work pins you down to your bed, with a bit of headache on the side, but you make the effort to sit up, since all your sisters are already trudging outside.
You join the column along the well-known forest path, but you suddenly slow your pace down, scratching your head. While looking for another way to catch up with them, you wander off to a tall and beautiful plant stalk. Something in it makes you want to climb on top. You reach a pretty-looking leaf. The uncontrolled desire to bite your teeth in it slowly arises. As your teeth go deeper into the leaf, a sudden shock travels down your spine – you are no longer the one who controls your body.
You can’t pull away from the grip of the invisible pliers that hold your mouth and limbs. Your body stops moving – a paralysing fear runs through your veins. Your muscles cringe and stop shivering, your vision becomes hazy. A dwindling sensation, like a worm wriggling and growing inside your brain, is the last thing you will feel as your grip on life loosens. You pass out. Forever.
What the Fungi Was That?
No, that’s not just another horror film, although it will probably top the charts of the ant cinemas in formicaries throughout the world. In this article, we will explore the world of Ophiocordyceps fungus – a special kind of evil in the ant-verse. It’s a parasite that absorbs an insect’s body and uses it as a host to grow and spread its spores around a large area, which spores can then latch on to other hosts and continue the cycle. Pretty terrifying life choices.
The Ophiocordyceps unilateralis is an entomopathogen, which means a fungus that attacks insects. Alfred Russel Wallace, a British scientist, found it in 1859. The fungus’ natural habitat is tropical rainforests, but it can be seen in other territories as well, such as the US.
The Zombie Ant Life Cycle
The fungus starts its life as a spore that lands on the ant’s body or attaches itself to it with its sticky surface, waiting patiently on one of the many ant trails throughout the forest. Then, the spore fuses with the ant’s body and exercises an amount of pressure, equal to that inside a Boing jet tire, to make its way through the exoskeleton of the insect. There, the spore reaches the ant’s brain, causing its host to act weird. That’s easily spotted by the other workers and warriors that drag the infected ant away and dump it into their “ant graves”.
In many cases, the ant itself goes to a tall plant stalk near a trail and climbs until it gets to a well-positioned leaf on top of that trail. There, the insect bites into the main vein of the leaf and firmly attaches itself there where it stays until its death, which usually takes between 4 to 10 days. At this point, the fearsome zombie puppet master starts growing inside the victim’s head and kills the ant. For the second time, the cordyceps applies enormous pressure to erupt from the ant’s head and form a stalk, which will drop its spores onto its next victims.
But why this weird zombie-like behaviour? Does the ant still control a bit of its body so that it can escape away from the nest and save its sisters while there’s still time? Recent scientific research shows that this is certainly not the case. In order to determine the reason, the team of scientists set up several ant nests with infected ants inside them. The results show that spores could never fully develop inside the nest as the infected ants either died out or were carried away by other workers. Only by finding the perfect leaf with the optimal conditions can the cordyceps be able to grow undisturbed.
Read more about ants life cycle.
The Host Species
The most popular cordyceps pawns are the carpenter ants – species that are widespread in the rainforests and active during the night. In order to protect its population alongside discovering the infected individuals, the ant society spreads its daily tasks amongst older and younger workers so that the older ones undertake riskier jobs, such as exploring and maintaining the trails. This way, if an ant got infected, it would have died of old age soon anyway.
However, it turns out that the cordyceps’ appetite is by far not restricted to carpenter ants. There are different spore species, and each of them specialises in a particular insect, expanding its victim scope way beyond the ant kingdom. Well, there’s also a tiny exception here, namely the US cordyceps, which is able to attack two different ant types.
So, are ants on their own when it comes to controlling the spread of fungus inside their nests? Of course, the answer is no – if it wasn’t already bizarre enough, O. unilateralis is also often infected by another type of fungus, which numbs its reproductive functions. Thus, the ways for an ant colony to be completely devastated go down by one more.
Image Source: Wikipedia