Do all Cordyceps grow on insects?

I was asked this question by Dan. The simple answer is no. When I called this blog 'allthingscordyceps' I knew I was walking into a scientific/taxonomic minefield. After all, I helped to create that minefield (see reference below if you want the boring science). What I am calling 'Cordyceps' here are many different genera – but all related.

How related?

'Cordyceps' and relatives belong to an order called the Hypocreales. Us humans are in an order that includes gorillas, chimpanzees, orang-utans and so many other primates. The Primates is an order.

The 'Cordyceps' group are generally called 'insect fungi'. But within that group there are some that have learned to infect close relatives of insects such as spiders, mites and nematodes. Well not so much learning. It comes down to an accidental switch from one host to another. In the same way that bird flu jumped from chickens to us and in the same way that HIV jumped from African primates to us!

'Cordyceps' are able to 'eat' their way through chitin which makes up the outer 'skin' of many invertebrates such as insects and spiders. As a result 'Cordyceps' has managed to become a pathogen of insects and spiders. But fungi also use chitin in their cell walls. Consequently, there are some 'Cordyceps' that infect and kill other fungi.

Erm.... not to scare people but.... A very small number of the 'Cordyceps' group are opportunistic pathogens that go after whatever they can. And that includes us – Homo sapiens! For most of us there is nothing to worry about. I have worked with 'Cordyceps' for thirty years and still don't have one growing out of me. At least not yet.

The few that can make use of us infect people who are immuno-compromised i.e. people whose immune system is not working properly. Reasons for this are many. The most obvious is HIV. But malnutrition and over-use of pharmaceutical medicines are other reasons for the immune system to either give up or get lazy. So, next time you feel a fever coming on.... Lay off the antibiotics and let your immune system sort the problem out. Otherwise you might wake up to find a mushroom growing from your stomach a la John Hurt in Alien.

References:

Sung, G-H., Hywel-Jones, N.L. Sung, J-M, Luangsa-ard, J.J., Shrestha, B. & Spatafora, J.W. (2007). Phylogenetic classification of Cordyceps and the clavicipitaceous fungi. Studies in Mycology 57: 5-59.