Warning, zombies are on the attack! And not just any zombies, whole colonies of zombie ants. When these insects get infected by a fungus they seem to completely lose control of their bodies. Called Ophiocordyceps unilateralis, the fungal parasite forces the ants to climb up the stem of a plant and then hold onto a leaf with their mandibles until they die. The decomposition of the corpse then releases the spores of the fungus to better infect the victim’s companions.
So far, scientists have suspected Ophiocordyceps unilateralis of directly attacking the brain of the ants in order to gain control. But a team’s work from the American University of Penn State in the United States has just revealed that this is not the case. The fungal parasite directly surrounds the insects' muscles and inserts itself in order to create a network capable of having control over the victim's movements.
Ants in a trance, cut into slices
To reach this conclusion published in PNAS, American entomologists have voluntarily infected ants with Ophiocordyceps unilateralis. They then cut the insect into multiple 50-nanometer slices, then scanned each one with an electron microscope.
‘By overlapping these layers, we were able to reconstruct them in 3D, and thus obtain a microscopic picture of the interaction between the fungus and its host, with an incredible resolution,’ says David Hughes, Associate Professor of Entomology at Penn State, who is enthusiastic about this feat. ‘It offers an unprecedented vision of how the manipulator controls its host.’ And the technical performance does not end there.
Researchers have also developed an artificial intelligence to analyse the images and to distinguish the cells of the ants from those of the fungus. They were able to observe that the fungal cells invaded the entire body of the insect, from its head to its legs, through its chest and abdomen, thus forming a true network. This fungus is in a way disguised as an ant and is able to manipulate the insect like a puppet.
The brain spared
But after examination of the brain surprisingly it revealed that there was no form of fungal life in this organ. It is probably preserved by the parasite to keep the ant alive long enough for it to perform its zombie mission. This is a guarantee for the fungus that the insect will reach the lower part of a leaf before its death ensuring that the spores spread properly.
Entomologists nonetheless assume there is a chemical attack by the fungus on the brains of its victims. Even if it does not settle there in the brain, the fungus could act at a distance by injecting certain substances into it. ‘We are planning more in-depth research to determine the precise role of the brain and to better understand how the fungus controls it,’ concludes David Hughes.
Even if some of the secrets of this invader have been solved, the infected ants have not yet revealed all of their mysteries. Beware, these zombie colonies are likely to go on the attack at any time!