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Ophiocordyceps unilateralis, commonly known as zombie-ant fungus, is an insect-pathogenic fungus, discovered by the British naturalist Alfred Russel Wallace in 1859.

Zombie ants, infected by the Ophiocordyceps unilateralis fungus, are predominantly found in tropical rainforests. However, they can also be found in warm-temperate forest systems. The fungus primarily targets ants from the tribe Camponotini, including carpenter ants (genus Camponotus). O. unilateralis infects ants of the tribe Camponotini, with the full pathogenesis being characterized by alteration of the behavioral patterns of the infected ant. Infected hosts leave their canopy nests and foraging trails for the forest floor, an area with a temperature and humidity suitable for fungal growth; they then use their mandibles to attach themselves to a major vein on the underside of a leaf, where the host remains after its eventual death. The process, leading up to mortality, takes 4–10 days, and includes a reproductive stage where fruiting bodies grow from the ant's head, rupturing to release the fungus's spores. O. unilateralis is, in turn, also susceptible to fungal infection itself, an occurrence that can limit its impact on ant populations, which has otherwise been known to devastate ant colonies. Related species, like Tolypocladium inflatum produce secondary metabolites that have been a source of valuable pharmaceuticals. Organisms like O. unilateralis have often evolved to produce specific metabolites for their antibacterial and/or host modulating activities.

After years of research, the taxonomy of Ophiocordyceps unilateralis is becoming increasingly clear.

Fungi able to parasitize ants were also included in the transfer, such as Cordyceps unilateralis which was later renamed Ophiocordyceps unilateralis.

The fungus's scientific name is sometimes written as Ophiocordyceps unilateralis sensu lato, which means 'in the broad sense', because the species actually represents a complex of many species within O. unilateralis. In 2011, it was hypothesized that the zombie-ant fungus could actually be described as a complex of species which are host-specific, meaning that one O. unilateralis species can only successfully infect and manipulate one host ant species. The asexual morphologies made it possible to distinguish two different clades mainly composed of species associated with ants which they termed "O. unilateralis core clade" and "O. kniphofioides subclade." Species within the O. unilateralis core clade as described in 2018:

The O. unilateralis core clade, as described in 2018, has distinct morphological characteristics.

Sometimes the canopy gaps are too difficult to cross, so the ants' trails descend to the forest floor where they are exposed to O. unilateralis spores. Like other fungi pathogenic to insects in the genus Ophiocordyceps, the fungus targets a specific host species, Camponotus leonardi; despite this, the fungus may parasitize other closely related species of ants with lesser degrees of host manipulation and reproductive success.

Effects of O. unilateralis on the host have been found to vary according to host species.

A 48-million-year-old fossil of a leaf stem exhibiting dumbbell-shaped marks characteristic of those made by an ant in the death-grip of Ophiocordyceps unilateralis was discovered in the Messel pit (Germany).

O. unilateralis suffers from an unidentified fungal hyperparasite, reported in the lay press as the "antizombie-fungus fungus", that results in only 6–7% of sporangia being viable, limiting the damage O. unilateralis inflicts on ant colonies.

Therefore, O. unilateralis controls the ant's behavior and this manipulation represents an adaptation for the fungus where natural selection acts on its genes, increasing the fungus' fitness.

In the video game series The Last of Us, Ophiocordyceps unilateralis has evolved to infect humans, thus creating zombie-like enemies in the game. The video game Cult of the Lamb features an ant character named Sozo who is implied to be under the influence of a parasitic fungus similar in nature to Ophiocordyceps unilateralis. The video game Grounded by Obsidian Entertainment has a similar type of fungal infection, known as "Fungal Growth", that portrays a few of Ophiocordyceps unilateralis behaviors.

Quick Facts

• Zombie ants, infected by the Ophiocordyceps unilateralis fungus, are predominantly found in tropical rainforests.
• O. unilateralis is, in turn, also susceptible to fungal infection itself, an occurrence that can limit its impact on ant populations, which has otherwise been known to devastate ant colonies.
• Organisms like O. unilateralis have often evolved to produce specific metabolites for their antibacterial and/or host modulating activities.
• The fungus's scientific name is sometimes written as Ophiocordyceps unilateralis sensu lato, which means 'in the broad sense', because the species actually represents a complex of many species within O. unilateralis.
• O. unilateralis infects ants of the tribe Camponotini, with the full pathogenesis being characterized by alteration of the behavioral patterns of the infected ant.

Source material: Wikipedia - "Ophiocordyceps unilateralis". Adapted and summarized for DiscoverScroll. Original contributors are credited through the linked Wikipedia article. Read original on Wikipedia. CC BY-SA 4.0. Changes were made from the original.