Attack of the killer fungus

by Ranjini Murali

 

When Cordyceps infects insects, it takes over their brains and changes the way the insect behaves

 

The ant was in hurry. He had to get to the nest before nightfall and he still had a long way to go. Determined not to let his weary feet buckle, he pushed forward. In his haste, he unconsciously rubbed against a leaf. A tiny, miniscule spore attached itself to the ant’s back. Blissfully unaware of the hitchhiker, the ant hurried on.

The ant woke up the next day feeling very ill and his head felt heavy. His brain seemed muddled and it was spewing out the strangest idea. He’d find himself wistfully looking at a green leaf on the large fig tree close to his work site and think that nothing would make him happier than to climb up and cling to it. When this happened, he’d shake his head, snap out of his reverie and tell himself to get on with his work.

However, toward the end of the day, this thought seemed to recur more frequently and it became harder to push away. By the next morning this was the only thought he had. He hurried out of his nest and straight to the large fig tree he was looking at the previous day. His eyes traversed the length of the trunk, finally lighting upon a pale green leaf. It was neither too young nor too old. He made his way up to it and using his sharp pincers, he dug right into the juicy mid-vein, like he never meant to let go.

An immense sense of peace stole over him. There was nothing else he’d rather be doing. He was happy. That was the last thought that ran through his head, before he stopped having any thoughts at all.

Inside the ant’s brain, the tiny spore smiled to himself. He had done his job well. He had managed to pull on the right nerves to get the innocent ant to do exactly what he wanted him to do. The spore had cunningly taken over the ant’s mind, making him a zombie with no thought of his own. He had painstakingly worked through the ant’s system, slowly replacing it with his own body. It was finally time for his hard work to pay off. He slowly started flexing his tiny filaments, inching his way out of the ant’s brain. The spore got all the energy he needed from the dead ant’s body. He pushed through the hard outer skin and soon the tips of his filaments were tingling, gently stroked by the cool breeze. Boosted by this, eager to see the outside world, his filaments grew longer.

The spore belonged to a deadly group of fungi called Cordyceps . Fungi are neither plants nor animals and instead form a kingdom of their own called Kingdom Fungi. Fungi are all around us – in the air we breathe, in the water we drink, in the soil we walk on. Some are beneficial, some are deadly and most don’t really affect us at all. There are innumerable fungi. Some are so small that you cannot see them and some can be seen by us.

Cordyceps is a group of fungi which we can see with our eyes. This fungus is capable of infecting insects and taking over their brains. In this group there are many different kinds of fungi which can take over insects. These fungi get into the insect’s system and sometimes change the way the insects behave so that the insect will give the fungus the best chance of surviving and spreading. And in the process the fungus kills the insect. Some fungi, like Spore from our story, control the different ants and make them climb up plants and attach themselves there. The place where the ants attach themselves has ideal important conditions like temperature and humidity that would allow the fungus to grow and spread its spores as far as possible. This ability of the fungus to change an insect’s behaviour evolved 48 million years ago!

This article appeared in the Hindu in School on 1 August 2012.

Picture: Death by mind control – Cordyceps is a type of fungus that can be seen by the naked eye.
Credit: Divya Mudappa