Today’s Story from the Museum Floor by Bryony from the Visitor Team takes a closer look at one of the most unusual objects from our botany collection.
And for more about plants, have a look at the Curator’s blog, Herbology Manchester.
Cordyceps, the Zombie Fungus
It’s Hallowe’en again, and you all know what that means… it’s our Stories from the Museum Floor Hallowe’en blog post, of course!
There are plenty of spooky things to write about in a museum. You might recall our post about the Death’s Head hawk moth, or perhaps the one about ancient Egyptian mummies … but would you expect to find … zombies?
Yes, we’ve got some real-life zombie specimens here in the museum. Now, brace yourselves, because this could get scary …
Cordyceps fungus on caterpillars, Nature’s Library, Manchester Museum. Cordyceps militaris is on the left, and Ophiocordyceps robertsii, right.
Don’t know what you’re looking at? Doesn’t look too sinister? Maybe you’ll change your mind when you find out a bit more about it …
When a Cordyceps or Ophiocordyceps spore lands on a creature, specifically an ant, it releases enzymes to ensure the spore burrows its way into the body, with different enzymes working to penetrate the different layers.
The fungus then stays inside the ant, branching out into different parts. It enters the brain, and takes over the pathways, interrupting their normal processes and starting to input its own instructions. For ants, a social insect, they often notice that one of their own is acting in a horrifying, un-antlike way and they try to carry them away, as far away from the nest as possible, because of what happens next.
The insect’s behaviour is dictated, down to the tiniest details, to provide the optimum site for the insect to die and the fungus to mature. Once the insect has served its purpose, the body at last expires.
And then … the important part for the fungus. The fruiting body emerges.
(WARNING: Not for the faint-hearted. The whole video tells the whole story, or skip to 1:02 to see the important bit – the sprouting of the fungus out of the ant’s head.)
The really extraordinary thing about it (apart from how gruesome it looks) is the high degree of control the fungus exerts over the behaviour of the host before their grisly end. Depending on the species it infects, it can cause them to bury themselves alive in the soil, or climb a tree and bite onto the branch to hold on, or other behaviours designed to provide the optimum conditions to serve the fungi’s purpose.
To give you an idea of how specific this is, one study of a species of ants (Camponotus leonardi) in Thailand found that, with an almost perfect degree of accuracy, the fungus controlled the ants to find a nearby plant, in an area with 94-95% humidity and with a temperature of between 20 and 30°C, climb up to a height of 25cm above the ground, on the North side of the plant, find a leaf vein and latch onto it with their jaws to die there as the fungus sprouts from their heads. This way, the fungus is able to ensure exactly ideal conditions for the spores to spread from the tip of the fruiting body that erupts from the ant’s head, affecting as many ants as possible.
It’s very easy to feel disturbed by the process! There’s no wonder that it’s been used as an inspiration for fictional zombie apocalypses, for example in the Cordyceps Trilogy by Ian Duncan; the book and movie The Girl With All The Gifts by Mike Carey; video games like The Last of Us; or death metal songs such as Cordyceps Humanis by the band Cephalic Carnage.
Examples of the zombies from the video game ‘The Last of Us’ (2013). You can see the fruiting bodies of a Cordyceps-style fungus coming out of some of the zombies’ faces. Book 2 in the Cordyceps Trilogy by Ian Duncan, and characters looking at a fruiting body from The Girl With All The Gifts (2016). (From: www.technobuffalo.com, tested.com, www.amazon.co.uk and flickeringmyth.com)
So, knowing what you now know about this fungus, would you want to … ingest it?
Well, oddly, people often do exactly that!
Some tempting Cordyceps (and pollen) dark chocolate, a healthy pork and Cordyceps broth, and a lovely pick-me-up drink … with Cordyceps. (From: hifasdaterra.co.uk, supremeginseng.com and international.foursigmatic.com)
Would you try it, knowing what you now know about this group of fungi, and what they can do to other living things?
Well, in certain parts of the world, they have been doing just that for hundreds of years, and there have, so far, been no (known) zombie apocalypses. In East Asia particularly a species called Ophiocordyceps sinensis (or simply ‘Cordyceps sinesis’ by non-scientists) has long been sought for its health benefits – it is so valued, in fact, that in recent years as it has become endangered from over-harvesting, people have even murdered each other as part of their disputes over it! It is now worth more than its weight in gold. It engineers its hosts so exactingly because it needs such specific conditions; so specific, in fact, that it is impossible to grow commercially, so the collected species get rarer and rarer.
Traditionally, it was seen as a good cure-all, as well as being an aphrodisiac (as are most disgusting foodstuffs) which seems to be more of a placebo effect than anything else – but there is evidence to suggest it might actually have a beneficial effect for certain organs, such as the liver. That is, if the thought of eating it doesn’t make you feel more ill.
Fun fact: the Chinese Olympic team attributed their unexpected success in the 1996 Olympic Games to regularly taking Cordyceps!
So, could Cordyceps ever turn on us and make us into zombies? Well, about 60% of the infectious diseases affecting humans today originated with another species – these infections are called zoonoses – but these are more usually bacteria and viruses, not fungi. Phew! And Cordyceps have evolved to be very species-specific – in order to programme their hosts with such complex behaviour, they need very exact control of the specific neural pathways in the brain – there are about 350 species that are infected by Cordyceps, and just as many species of Cordyceps to match. Luckily, Cordyceps don’t affect any vertebrate that we know of, only insects (and one tarantula species, but that’s still nowhere near us mammals). It has been known to affect very closely related species other than the one it is specifically evolved for, but although this can sometimes alter their behaviour a little, the ‘programming’ doesn’t work as it should. It doesn’t have any adverse effect on humans.
There’s even a UK species – Cordyceps militaris, which we have on display. This is a species that buries itself throughout the summer and autumn time, but often is hard to spot in the wild because of the grass and moss usually surrounding its fruiting body. Not to mention that unless you did some digging, you wouldn’t know about the poor zombified caterpillar just below the surface.
Left, Cordyceps militaris in the wild, and, right, illustration of specimen on the Nature’s Library gallery, Manchester Museum. (From: fungi.myspecies.info).
So, this Hallowe’en, as you’re dressed up and tramping across fields to trick-or-treat at peoples’ houses, spare a thought for the real horror show, which could even be entombed right beneath your feet on that spooky night …
P.S. Also, if you would like more Cordyceps encounters, we have loaned a few (along with other plant and fungal specimens) to the current Mehreen Murtaza exhibition at Manchester Art Gallery, part of the New North and South programme of events. It will be there until the 4th of February, 2018. To tempt you even more, here are some pictures:
More Cordyceps specimens, including one on the pupa of an Ichneumon wasp, itself a parasite.
With special thanks to Rachel Webster, Curator of Botany at Manchester Museum, for the pictures, and for the support and advice with this post.
P.P.S. Want to find out more?