There is something quite intriguing about the idea of mind control. As a concept, it has been around for decades, appearing most often in the creative projects of science fiction writers. Some of the most famous examples include George Orwell’s Nineteen Eighty-Four and the X-Men comic book series – where characters such as Professor Xavier can read and control other people’s minds.
The latter, in particular, may seem far-fetched in reality, but manipulation of the brain is far more common than you may think. Hidden amongst the world’s lush rainforests, stagnant ponds and lush meadows, some parasites species have mastered the art.
The parasitic way of life takes advantage of other organisms and negatively impacts their lives, usually through a loss of resources, injury or death. It is utilised as a life strategy by a rich diversity of species, including bacteria, worms and even birds. But infecting a host and using it for personal gain is not always an easy thing for a parasite to do, meaning some have developed unique – and often rather sinister – forms of mind control.
One of the most famous examples can be attributed to Ophiocordyceps unilateralis, an organism known less scientifically as the zombie-ant fungus. This pathogenic species was first identified in 1859 by naturalist Alfred Russel Wallace. It lives in tropical forests worldwide, where its spores reside on the forest floor and lie in wait for a particular species of ant to pass by.
When one of these ants inadvertently picks up a spore, it breaks through the exoskeleton and spreads within the ant’s body over a few days. Once developed, the fungus begins to take hold of its host, forcing the ant to break away from the colony and climb zombie-like up the stem of a nearby plant. When it reaches an area suitable for the fungus to grow, the ant clamps down on the plant with its mandibles. This involuntary act is known as the death grip and is the last thing the ant ever does before being killed by its fungal host.
After death, the fungus explodes out of the ant’s head in a display worthy of a good horror movie before completing its life cycle by releasing its spores into the environment. In doing so, it maximises its reproductive success. The impact on the ant is not so beneficial, and some studies have found that entire colonies can be wiped out in areas where the fungus is active, leading to the formation of eerie ‘ant graveyards’.
Worryingly, the effects of mind-controlling parasites are not just limited to simple life-forms. In 2002, an article published in BMC Infectious Diseases found that humans infected with the protozoan species, Toxoplasma gondii, were more likely to be involved in traffic accidents. These findings have been backed up by subsequent studies and others that have found that the parasite may be associated with increased risk-taking, greater levels of rage, and even a higher chance of developing schizophrenia. Considering at least 30% of the global population is thought to be infected with the parasite, these findings are troublesome, to say the least.
The species can be transmitted to humans via undercooked meat and unwashed vegetables, although the prime source of the parasite can be identified simply by locating your pet cat. Toxoplasma gondii usually begins its life cycle in a rodent. However, it can only reproduce in the digestive tract of our furry feline friends. To make this transition between species, it has to be eaten, and the species speeds up the process by manipulating the rodent’s brain to give it an attraction to cats. Infected rodents are also far more prone to risk-taking, increasing the chances that they’ll be caught and eaten.
So, where do humans come into all of this? Well, we are simply intermediate hosts - the parasitic equivalent of a mobile life-support vessel. It is sporadic for us to show any physical symptoms of the infection, and the effects on the human brain are still not fully understood. Nevertheless, the resourcefulness of parasites such as Toxoplasma gondii is, from an evolutionary perspective at least, hard not to admire.
Hughes, D.P., Andersen, S.B., Hywel-Jones, N.L., Himaman, W., Billen, J. and Boomsma, J.J., 2011. Behavioral mechanisms and morphological symptoms of zombie ants dying from fungal infection. BMC Ecology, 11(1), pp.1-10.
Flegr, J., Havlícek, J., Kodym, P., Malý, M. and Smahel, Z., 2002. Increased risk of traffic accidents in subjects with latent toxoplasmosis: a retrospective case-control study. BMC Infectious Diseases, 2(1), pp.1-6.