Fungi have been ‘zombifying’ insects for 99 million years

Nearly 100 million years ago, a drop of tree resin captured a gruesome scene: a fungus bursting from the body of a young ant. That resin eventually hardened into amber. Today, this fossil is offering insight into a fungus that’s become famous for hijacking its victims’ brains. The ancient insect’s demise suggests such fungi have been infecting ants twice as long as scientists had thought.  

That fungus is called Ophiocordyceps (OH-fee-oh-KOR-dih-seps). It infects — and “zombifies” — insects such as flies, caterpillars and ants.  

Right before an infected ant dies, it will have a sudden urge to leave its nest and climb up onto a high leaf. There, it will bite down with a death grip. In one final gory moment, the fungus will then explode from the ant’s back.  

That blast releases spores that can now infect the fungus’ next victims. 

How these fungi infect insects and control their behavior is fairly well known. But little had been known about when this bone-chilling behavior first began. Why? The soft bodies of fungi hardly ever become fossils. Even rarer, the researchers note, is finding a fossil insect with the fungus still inside. 

A chance discovery 

It was a stroke of luck when Yuhui Zhuang stumbled across the ant fossil. The paleontologist had been digging through samples in his lab’s basement at Yunnan University in Kunming, China.  

When he saw something sticking out of one ant’s back, Zhuang first assumed it was a developing wing. Both ant queens and males have wings. But a 3-D image of the fossil revealed something different.  

To Zhuang’s surprise, a fungus was sprouting from a gland on the ant’s back.  

That fungus was remarkably similar to modern-day Ophiocordyceps — the “zombie fungus.” Its spores had a similar shape. Plus, the spores were growing out of a domelike structure that had burst from the insect’s back. 

Intrigued, Zhuang went hunting for other infected insect fossils. That search turned up a fungus-ridden fly in a different collection of specimens. This insect, too, had been trapped in amber. And the fungus in it looked a lot like modern-day Ophiocordyceps. 

Zhuang is part of a team that shared its new findings June 11. They appear in Proceedings of the Royal Society B. 

A history of zombie fungi 

The ant and fly fossils were both 99 million years old. It seems that ancestors of today’s “zombie fungi” were already infecting multiple groups of insects back then, says Conrad Labandeira. This paleontologist did not take part in the new study. He works at the National Museum of Natural History. It’s in Washington, D.C. 

The ant and fly fossils suggest Ophiocordyceps evolved alongside its victims, says Zhuang. The oldest fossil ant ever found is 113 million years old. So fungi might have been infecting the ancestors of ants almost since they first appeared. 

The ant in the newfound fossil was a pupa. During this stage of an ant’s life, it can’t move, Zhuang notes. So the fungus was likely not controlling this ant’s behavior.  

Perhaps a grown ant noticed the pupa was infected and removed it from the nest, he says. Outside, the fungus would now have released its spores in search of its next victim. 

For an ant or a fly, Labandeira says, this is “a pretty gruesome story.”