 the conditions in these places are favorable for O. unilateralis. This leads to places, called graveyards, that have a high density of corpses. Any healthy ant happening to walk through such an area will likely become infected by the deadly spores.
When O. unilateralis spores come into contact with an ant, they adhere to it and start to penetrate its cuticle. After this, fungal cells start to infest the ant’s entire body and begin to alter its behavior. The infected ant then leaves the colony and starts the trek down toward the forest floor. Once a perfect spot is reached, the ant will bite the vein of a leaf and die with its jaws locked in place. This is known as the “death grip”, and keeps the ant from falling off the leaf. Any ants that end up dying within the colony due to infection will be carried far away by other workers. Within a few days, the stroma, or stalk, of the fungus will erupt from the back of its host’s head and develop a stromal plate that releases spores when mature. By this point, most of the ant’s original tissue has been replaced by fungus.
The ants in the video below are not Camponotus or Polyrhachis ants, and the fungus is not O. unilateralis so the hosts show a different behavior. However, it still illustrates the process well.
What a horror it would be if humans were susceptible to such a fate! The question is, could this actually happen? Let’s consider the ant brain for a moment. It has all the general features of a typical insect brain and is very simple compared to a vertebrate brain. However, ants have more well developed areas associated with memory and learning. These “higher” functions are controlled by the – get this – mushroom bodies (it’s funny because we’re talking about fungus taking over an ant brain here and they just happen to have structures called mushroom bodies. Mushroom bodies are much larger in worker ants than they are in the male soldiers, which are more hard wired or pre-programmed. Workers must navigate varying spacio-temporal environments using multiple cues and also remember where food is and where home is. For ants, workers are the most “intelligent”. Still, one lone worker is of no use. It takes the whole colony to have a properly functioning and flourishing nest. An entire colony of ants, which can be up to millions of individuals, does not even come close to matching the complexity of a single human brain. If a fungus were to develop an ability to infect and alter the behavior of humans, this would probably take a ridiculously long time to evolve. Human beings would most likely not even be around any longer. But, let’s just roll with it and say that this could happen. What would it be like and how does The Last of Us compare?
We’ll start with the mode of infection. In the video game, people seem to become infected by breathing in the spores of the mutant O. unilateralis strain. Those who wear a special breathing bask in spore filled areas do not become infected. This appears to check out. Human skin is likely to be much less susceptible to becoming invaded by spores, simply because it is so much thicker and has many more layers than insect cuticle. Other fungi are able to infect hosts via inhalation (like some molds), so it would be no different for a mutant fungus; the infection would just result in a different pathology. So getting infected by this fungus is not in question if you breathe the spores in, but you can also fall victim if there is an exchange of bodily fluids, such as from a bite. This is logical as well. If the fungus has infiltrated an infected person’s system as in ants, bodily fluids like saliva and blood may contain fungal cells. These could easily be passed on to a healthy human.
What about the behavioral and morphological alterations? In The Last of Us, any infected individual, even in the early stages, is being driven by the fungus’ gene expression and aims to spread the spores or cells to as many others as possible. There are four main stages of infection from this mutant O. unilateralis: Runners, Stalkers, Clickers, and Bloaters. All of t