A mind-controlling fungus might sound like something out of a horror movie but if you happen to be a carpenter ant it is a real and present danger. Found in the tropical rainforests of Thailand and Brazil, there is a species of fungi called Ophiocordyceps unilateralis which parasitizes the local ants, infecting them through their exoskeleton. From there is alters it victims behaviour, possibly by releasing certain chemicals, the upshot of which is that the ant abandons its colony, climbs up to the top of a nearby tall plant and then clamps onto a leaf in what is known as a ‘death grip’. The ant then dies, still clinging tenaciously to its leaf, and a tall stalk grows out of its head. This is the fruiting body of the fungus and it releases spores which then start the whole process over again. Exactly how the fungi manipulates its host to such an impressive degree still isn’t well understood but there is evidence that such interactions are far more ancient then you might expect.
The Messel Pit in Germany is the source of some of the most impressive Palaeogene fossils in the world. It was, until the 1960s, the site of an oil shale mine but is now better known for the fossils of over a 1000 different species which have been discovered there. All date to the Eocene, a period in Earth’s history between 57-36 million years ago and at the time Messel was a large lake, situated somewhat south of its modern-day location giving it a subtropical climate. Many of the animals and plants are beautifully preserved and some even include fossilised feathers, hair or stomach contents. Many fossilised leaves have also been recovered, and it is one of these leaves which led to the discovery of ancient mind-control.
The specimen itself is 48 million years old but when it was initially collected it didn’t attract much interest, and was stored at the Smithsonian Institution’s National Museum of Natural History in Washington DC for many years. Then in 2010 a paper was published in Biology Letters which highlighted some strange markings preserved on the leaf’s surface. The work was led by behavioural ecologist David Hughes who had studied the relationship of ants and parasitic fungi in modern-day Thailand and was intrigued by the possibility of discovering similar relationships in the fossil record. This particular leaf showed clear signs of damage characteristic of an infected ant’s ‘death-grip’. The level of preservation was so good, and the level of detail so correspondingly fine, that it was even possible to discount other damaging insect activities such as vein-cutting. Instead the study concluded that the small, dumb-bell shaped marks eerily resembled the modern scars left by dying carpenter ants infected by Ophiocordyceps.
No body fossils of infected ants have yet been discovered so it is impossible to say which ant species bit this particular leaf, or what fungi had infected it but it seems possible it was a relative of Ophiocordyceps. Either way this discovery shows that this strange and complex relationship was already well established by 48 million years ago and is presumably therefore even older then this.
As a final note there is some good news for modern day carpenter ants and their kin – it turns out that Ophiocordyceps doesn’t have everything its own way. In 2012 a study was announced by Pennsylvania State University, again led by David Hughes as part of an international team, which revealed that the mind-controlling parasite fungus is itself parasitized by another fungus. Known as a ‘hyperparasite’ this fungus infects and effectively castrates Ophiocordyceps, preventing it from releasing its spores once it has hatched out of the ant’s cadaver. As a result only around 6.5 percent of the spore-producing organs are actually capable of producing and releasing viable spores. It is this fact which prevents whole colonies being devastated by the fungus.
1. Evans, H.C. et al. 2011. Ophiocordyceps unilateralis. Communicative and Integrative Biology. 4(5) pp. 598-602. DOI: 10.4161/cib.4.5.16721
2. Hughes, D.P. et al. 2010. Ancient death-grip leaf scars reveal ant-fungal parasitism. Biology Letters. DOI: 10.1098/rsbl.2010.0521
3. Anderson, S.B. et al. 2012. Disease Dynamics in a Specialized Parasite of Ant Societies. PLOS One. DOI: 10.1371/journal.pone.0036352