Caterpillar Eating Fungus

It’s not too late in the year to find interesting things in our meadows. And I’d don’t mean 50 p coins…

About 3 weeks ago I found a very small, and unfamiliar orange fungal fruiting body at one edge of our close mown path which runs through our upper hay meadow. Not knowing what it was, I sent photos to Pat O’Reilly who has a fantastic website for fungi identification. Click here for more about Pat.  In addition I posted it on iSpot, the Natural History Museum/Open University website for all such mysteries. Click here for iSpot.

Within 24 hours 2 possible ID’s were suggested, one a rare form of Microglossom Earth Tongue fungus, the other the wonderfully named Scarlet Caterpillar Club fungus – Cordyceps militaris. So called because this is a fungus which specifically attacks the underground larvae or pupae of grassland moths, a so called entomopathogen. Once a fungal spore has germinated on the moth larval body, it has the ability to pierce the defensive chitinous external layer, invade the circulatory fluid system and then begin to grow a mycelium structure throughout all of the caterpillar’s body tissues. So it devours the caterpillar’s body, kills it and eventually, if environmental conditions are appropriate, will produce a fruiting body similar to the one shown here.

Armed with this name, and life cycle, I carefully dug round the fruiting body, and teased away the soil for confirmation – the photos below show the dark caterpillar sprouting the fruiting bodies, with what look like 2 or 3 more fruiting bodies at an early stage of development.

These fungi are not found very often – in part no doubt because they are quite tricky to spot, but also because they could easily and quickly be destroyed through slug damage. Most of our grassland mushrooms seem magnets for any slugs still left in the meadows, and hence don’t normally survive intact for many days. The fact that the fruiting bodies were just in the shorter grass of the mown path, and also that slug numbers have collapsed so dramatically this year in our meadows, probably explains why I did manage to find it.

Globally currently over 400 species of Cordyceps are described, and this particular one, and a Chinese cousin C. sinensis, have been recognised for some time as containing chemicals, particularly cordycepin, with a huge range of potential medicinal uses from cancer suppression through immunostimulation and even as a pre Viagra treatment for erectile dysfuntion.  Click here and here. So much so that for a number of years it has apparently been commercially grown on artificial media to enable harvesting of exactly the tiny fruiting bodies shown above. It’s fascinating that with so much Asian awareness of its therapeutic potential value, I’d never even heard of it before, let alone come across it.

Some intriguing thoughts occurred to me as I researched this. Firstly whether there are any such fungi which attack slugs in the same way? I couldn’t find any records at all however, and given this lack of slug predation, might slug slime have some protective anti-fungal properties? Click here for an insight into current research on this, and how slug slime’s antimicrobial properties might even be a valuable counter to human problems with MRSA in the future.

Secondly, given the apparently high heavy Nitrogen isotope content of Waxcap mushrooms as explained by Gareth Griffith in discussion of his research at the autumnal CMG meeting, might these Waxcap fungi be secret slug killers, or consumers? Might the reduction in slug numbers I’ve described in part be because of the increasing numbers of Waxcaps which we now find in our meadows??? Probably complete coincidence …

I thought this was the end of the matter, until last week whilst collecting fallen leaves from our mossy irregular croquet lawn, I found another. Then another. Then another. In the end a total of 9 separate fruiting bodies, marked by the hoops in the photo below. So a lot of dead moth caterpillars in this small section of diverse close cut “lawn”, which of course never gets chemical treatments of any kind.

Finally this week, I found the tallest of the lot, so the eleventh record here this year, growing in our lower wet hay meadow just beside a hay shed.

If you click here,, you can see the NBN records for this fungus. Only about 1,000 ever, from across the whole of the UK. So has 2018 been a particularly good year for them? Will I ever find any again?

It might be worth having a close look around your fields once the rain stops. Unlike several fungal fruiting bodies, these seem to survive for many days, if the slugs leave them alone, and they’ve even come through the heavy frosts we had a week ago, apparently unharmed.

Julian Wormald



4 thoughts on “Caterpillar Eating Fungus

  1. I’ve seen one this winter Julian in a sheep grazed field near me in Cilycwm and previously seen them up on the Black Mountain. Worth an entry on the Carms Fungi blog I think? Great photos!



  2. I was lucky enough to find two growing side by side, like your first pair, on one larva, in Derbyshire on October 31st 2015.
    I remember the date because we had gone for a walk in a ‘haunted’ valley, perhaps unwisely!
    (We’re not superstitious, but we still hurried a bit to get out of the valley before dark!)


  3. What a fascinating article, thanks Julian. For some reason, our field which usually has quite a few waxcaps has produced very few this year, it was very dry to the extent that there are patches where the grass has died. But further (and converse) to your comments about whether slug mucus protects them from fungal attack, some years back at Rothamsted we were trying to identify slug antifeedants which could be used to protect crops instead of using molluscicides. It occurred to us that lichens, well known for (i) growing very slowly, and (ii) often being found in damp habitats, might be a good place to look. It turned out that many lichens do produce slug antifeedants, and it seems to be the fungal part (mycobiont) of the fungus/alga association that produces them: Interestingly, lichens that grow in small cracks in rock (endolithic) don’t produce them, presumably because they are safe from slug grazing. The practical application was limited as is often the case with antifeedants from higher plants too, because they can be quite nasty chemicals, a case of being full of natural badness perhaps….


Leave a Reply

Fill in your details below or click an icon to log in: Logo

You are commenting using your account. Log Out /  Change )

Twitter picture

You are commenting using your Twitter account. Log Out /  Change )

Facebook photo

You are commenting using your Facebook account. Log Out /  Change )

Connecting to %s