Scarlet Caterpillarclub, Cordyceps militaris.

As a fan of both insects and fungi, I was thrilled to see my very first Scarlet Caterpillarclub fungus, Cordyceps militaris, on a trip to the Norfolk Brecks last Sunday.

I had wanted to see this species for some time and to find not just a single Cordyceps militaris but eleven of them in a single location, in short grass around an oak tree on a grassy heath, was absolutely stunning. The fungus is an infrequent find in the British Isles, and seems to be commoner in the north and west (note 1).

Scarlet Caterpillarclub is a parasitic fungus that grows on the larvae and pupae of moths. The unfortunate host is a caterpillar that has buried into the soil to pupate but is instead consumed by the fungus, which sends up a bright orange club through the turf to spread its spores. When viewed with a hand lens, the bottom of the club (the stipe) is smooth but the upper surface of the club looks bobbly. Cordyceps militaris is an ascomycete fungus and the bobbles are perithecia, small flask-shaped fruiting bodies which contain spores (note 2) .

If you gently extract a Scarlet Caterpillarclub from the soil it is possible to find its unfortunate host. We did this with one of the fungi we found; ours was still a caterpillar but the Lorn Natural History Group website has superb photographs of the fungus growing from both pupae and caterpillars (note 3). The fungus normally grows from the head end of its host.

Cordyceps militaris is the commonest of about a dozen Cordyceps species that have been recorded in the British Isles (note 4) and there are around 400 species worldwide. Cordyceps comes from two Latin words: cord, a club, and ceps, head. Militaris is also from Latin and may refer to the way this fungus attacks, overpowers and occupies its host.

Following DNA sequencing, some species of Cordyceps have now been moved to the genera Ophiocordyceps and Tolypocladium. Several species are so-called “zombie fungi” because of the way they take over an insect’s body and alter its behaviour.

Probably the most (in)famous example is Ophiocordyceps unilateralis, a parasite of carpenter ants, found in tropical forests. The fungus influences the ant’s behaviour, making it travel outside the nest to a more humid place suited to the fungus, removing its instinctive fear of heights and making it climb the stem of a plant, where it clamps its jaws around a leaf vein and waits to die. Fungal hyphae grow out of the ant’s feet to attach it more firmly to the plant and then the fungus digests the ant from within and sends a fruiting body out through the base of the ant’s head, to spread its spores. Some of these spores will infect another ant, to continue the lifecycle. Throughout the process, the fungus is absent from the ant’s brain and the fungus’ influence on the ant appears to be a chemical one, possibly through ergot alkaloids (chemically related to LSD) (note 5).

Ophiocordyceps sinensis, the Chinese Caterpillar Fungus, has a similar lifecycle to our Scarlet Caterpillarclub but is found in Tibet, Bhutan, Nepal, India and China and mainly infects the caterpillars of Thitarodes ghost moths (note 6).

These caterpillars spend their time under the ground, where they feed on roots. They can become infected with fungus spores through their mouth or skin as they move down through the soil. Once infected, a caterpillar moves slowly into a position ideal for spore dispersal (just the right depth for the fungus to push its club above the surface) and its skin changes colour from brown to milky white. Fungal hyphae fill the caterpillar’s body cavity and it is long dead by spring when the fungus sends a stalk up above ground and produces spores to infect the next generation of caterpillars.

The Chinese Caterpillar Fungus has been known about and used in Chinese medicine for generations (note 7). It has been used to treat an assortment of conditions including fatigue, respiratory and kidney diseases and cardiac dysfunction. Research is now being carried out to assess these medicinal properties (note 8).

Ophiocordyceps sinensis suddenly became a lot more popular in 1993 after two unknown female athletes, Wang Junxia and Qu Yunxia, broke records races in China’s National Games in Beijing and their trainer revealed that they had taken Ophiocordyceps sinensis supplements. 

The popularity of Chinese Caterpillar Fungus has had a major impact on the regions where it grows. On the plus side, it has provided much needed income and employment (for whole families) in mountainous areas. But as early as 2005, the New Scientist was reporting “Chinese fungus fad poses eco-threat“. By then the harvest from the Tibetan Plateau and Himalaya Region was around 140,000 kg per annum, with 2,000kg poached from Bhutan alone in 2002, and prices had reached some $7,000 a kilogram, half that of gold. By August 2012, the price had soared to $110,000 per kg in Beijing, almost three times the current price of gold.

Ophiocordyceps sinensis is only found in alpine meadows at altitudes of about 3000–5200 metres (note 9) and its range is retreating upwards as global warming takes hold. Harvesters scour the meadows and use a small pickaxe to remove a patch of grass, together with roots and topsoil, to reveal the fungus emerging from its host. The entire fungus and its attached caterpillar are removed intact, cleaned and sold to itinerant caterpillar fungus traders.

The annual collecting season lasts from about mid-May to mid-July. In this time, collectors can dig up whole meadows, cut alpine shrubs for fuel and dump rubbish, including human faeces which can contaminate water sources. The influx of thousands of people can disturb livestock and wildlife (including the rare Snow Leopard). There have also been some violent disputes over harvesting areas.

Not surprisingly, yields of Ophiocordyceps sinensis appear to be falling (note 10) and the sober conclusion to this tale of overexploitation is: “It now appears increasingly possible that caterpillar fungus, if not properly managed, may be a one-time ecological windfall rather than the inexhaustible resource it once appeared to be.”

Meanwhile, our very own Cordyceps militaris is being investigated too (see Das et. al 2010, for example). Like Ophiocordyceps sinensis, taking extracts of the fungus appears to improve tolerance to high intensity exercise and it may have uses in treating some cancers.

Large-scale artificial cultivation of Ophiocordyceps sinensis in its host is not possible, though small scale production is now taking place. But cultures of Cordyceps / Ophiocordyceps fungi grown without the fungal host – anamorphs (the asexual form of the fungus), grown in liquid cultures or in grain – allow suppliers to produce Cordyceps extracts and powders. The Real Mushrooms website explains more.

It is also possible to grow the sexual stage of Cordyceps militaris in bulk (minus caterpillar). Mushroom Revival, based in Austin in Texas, grow it on a vegan substrate and sell it as a dried fungus or as a tincture. A quick search online gives lots of results for various Cordyceps extracts for sale in the UK too. The Real Mushrooms website says that extracts of this form of the fungus contains the active ingredient cordycepin (3?-deoxyadenosine) in much higher amounts than Cordyceps sinensis.

Some websites say that Scarlet Caterpillarclub isn’t edible but Alan from Minnesota, a chef, offers a recipe on his Forager Chef website: Cordyceps with Linguine, Shallots, Watercress and Chives. He says the ones he bought from San Francisco “weren’t mind blowing, but they definitely weren’t bad“. He wonders whether the fungus tastes the same without its caterpillar – it’s a question of “terroir“.

I don’t plan to try Cordyceps any time soon, but for fans, the RealMushrooms website has links to recipes containing Cordyceps powder, including Sexy Mushroom Truffles and Muscle Recovery Bone Broth.

Cordyceps and Ophiocordyceps fungi have even inspired a video game, The Last of Us, which is set in a post-apocalyptic United States (note 11). In a world of Covid-19 and Trump, that seems a bit too real for comfort, so I’ll stick to going outdoors in the healthy air to look for more fascinating fungi.

Notes

Note 1 – A couple of years ago Norfolk Fungus Study Group found Scarlet Caterpillarclub in the grassland at Felbrigg Hall in North Norfolk, on one of their field trips (which I missed). At time of writing the NBN Atlas doesn’t include this record.

Note 2 – Some club fungi, such as Pipe Club (Typhula fistulosa), are Basidiomycetes.  In contrast to the Scarlet Caterpillarclub, their clubs have a smooth surface.

Note 3 – A variety of species are parasitised but the Lorn Natural History Group website says “The caterpillars are usually well decomposed and hard to identify with certainty”. This was certainly true of our specimen.

Note 4 – (So far) I have only seen the Scarlet Caterpillarclub.

Cordyceps ophioglossoides, the Snaketongue Truffleclub, Cordyceps capitata, the Drunmstick Truffleclub and Cordiceps longisegmentis, are three more British species, but instead of insects they parasitise another fungus, the False Truffle, Elaphomyces granulatus. Their clubs grow from the False Truffle’s underground tubers.

Note 5 – I recommend the book “Entangled Life – How Fungi Make Our Worlds, Change Our Minds and Shape Our Futures” by Merlin Sheldrake, The Bodley Head, London (2020) – Ophiocordyceps unilateralis is discussed in Chapter 4, “Mycelial Minds”.

Jennifer Lu’s National Geographic article “How a parasitic fungus turns ants into ‘zombies'” (April 2019) and its accompanying video are worth a read and watch.

See also “Fungi That Infect Insects: Altering Host Behavior and Beyond” by Shang et.al. (2015).

However, rather than kill their host, some Ophiocordyceps fungi actually help several Japanese species of Cicada to take up nutrients from their diet of plant sap, which is high in sugars, but low in other essential nutrients. See “How To Tame A Zombie Fungus” (Yong, 2018).

Note 6 – A review of Ophiocordyceps sinensis by Wang and Yao in 2011 found 56 potential insect hosts, primarily “ghost moth” larvae of the genus Thitarodes (37 species).

Note 7 – Although its use may go back some 2000 years, the first written references come from a fifteenth-century Tibetan medical text. The first mention in a Chinese medical text is in 1757.

A Chinese name for Ophiocordyceps sinensis is Dong chong xia cao. Like the Tibetan name yartsa gunbu, it means ‘winter worm, summer grass’. The fungus was once thought to transform from an animal to a plant during summer and back to an animal for the winter.

Note 8 – See, for example, Choda 2017 and Belwal 2019 and the RealMushrooms.com website.

Note 9 – Its habitat ecology (including soil types and associated plants) has been studied in Nepal by Sigdel et. al (2017).

Note 10 – For example, official yields in Nepal went from 3.1 kg in 2002 to 2442.4 kg in 2009, before dropping precipitously to just 1170.8 kg in 2011.

Note 11 – Kyle Hill wrote about the game and Cordyceps in the Scientific American blog in 2013: see “The Fungus that Reduced Humanity to The Last of Us“.