Zombies have gained a lot of popularity in the past years. Fortunately for us, zombies remain limited to our screens and the imagination of fictional writers. For some groups of organisms, however, infections by viruses, fungi or other invertebrates can take quite a different turn. For these species, a parasite will take control of their neural functions and control their behaviour. It is surprising to note that organisms apparently inoffensive like fungi (the ”mushrooms”) are able to take control of seemingly “more evolved” species like insects. One such example is 𝘖𝘱𝘩𝘪𝘰𝘤𝘰𝘳𝘥𝘺𝘤𝘦𝘱𝘴 𝘶𝘯𝘪𝘭𝘢𝘵𝘦𝘳𝘢𝘭𝘪𝘴 (Tul. & C.Tul.) Petch, a species famous for its ability to alter the minds of ants among other insects. A feat that earned them the name of “zombie ant fungus”.
Zombie ant fungus belongs to the genus 𝘖𝘱𝘩𝘪𝘰𝘤𝘰𝘳𝘥𝘺𝘤𝘦𝘱𝘴 in which a majority of species infect ants. However, other species can be referred to as “zombie fly fungus”, “zombie moth fungus” and “zombie stinkbug fungus” that exhibit similar mind-controlling behaviours on various organisms. They mostly infect insects or other invertebrates but not humans because our bodies have a higher temperature, which is not favorable for the reproduction of these fungi. Additionally, human bodies have a more advanced and complex immune system than those of insects, protecting us from 𝘖𝘱𝘩𝘪𝘰𝘤𝘰𝘳𝘥𝘺𝘤𝘦𝘱𝘴 infections. It is for these reasons that the zombie ant fungus selects ants as its preferred hosts rather than us, humans. Lucky us!
Zombie ant fungus has a range of strategies to control their victims. In the beginning, their spores patiently await their unsuspecting victims in the rainforest. Once the spores latch onto the ant’s body, it will start developing hypha, a filamentous structure which has a similar function to the root of plants, allowing nutrient absorption in fungus. The hypha will then penetrate the exoskeleton (sort of skin and skeleton in insects) of the ant and delve deep inside with the help of enzymes. Once inside the body, the fungus manipulates the ant’s brain using nerve toxins altering its behaviour. The infected ants leave their colony in the dry, hot canopy and descend to the humid understory. They will then express whole-body convulsions, often making the ant fall off the tree and preventing it from climbing back to the canopy.
At this point, the ant is nearing the end of its life. They will climb up the short vegetation near the forest floor. When the ant reaches a suitable environment, the fungus will force the ant to bite on a leaf (usually the midrib of the leaf) or stem. The mandibles are locked so tightly that they prevent the ant from falling even if it is hung upside down. The hyphae extend from the body openings and joints, which further anchor the ant to the leaf surface. Here comes the most scary part. A stalk-like structure emerged from the ant's head or neck. At the tip of the stalk, there is a fruit-like structure called ascoma. It is the sexual structure of the fungus that releases spores, enabling the infection of other unsuspecting ants, and continuing the life cycle of the fungus.
The zombie ant fungus is truly remarkable and could inspire fiction authors with their life cycles. Its uniqueness, however, is not confined to the rainforest. It can even be observed in unexpected places like Hong Kong. So look carefully for ants or other insects standing petrified on vegetation with long fungus stems emerging from their head or other joints. This phenomenon is one of the most intriguing relationships between fungi and animals. If you would like to meet these real live zombie makers, come and visit the Hong Kong Biodiversity Museum!
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