Nick Baker’s hidden Britain
The scarlet caterpillar-club
Right now, all over our damp islands, strange productions are afoot. It is fungi time and, if you want to immerse yourself in an alien world of jelly ear, drumstick truffle-club and hairy nuts disco, you have to look no further than these organisms for a bit of weirdness.
They’re most certainly a vital part of hidden Britain – their actions are essential to the recycling of nutrients and the health of our living systems. For the most part, their lives and operations occur unseen – secreted in the soil, in trees and dead vegetation, where they silently get on with doing their job, turning the dead, and sometimes the living, back to the soil. Among the most fascinating are those in the latter category, especially those that play a vital role in controlling and keeping in check insect numbers.
One such fungus is the scarlet caterpillar-club, Cordyceps militaris. Look out for its short (1–4cm long), bright, orangeyred digit pushing up from amongst meadow grass blades or woodland litter. Of the dozen or so Cordyceps species found
in the UK, only the scarlet caterpillar-club (AKA caterpillar killer) is this colour and has the granular texture.
It sometimes looks like a disembodied, rough-textured tongue, a sight sure to draw in a curious eye, but the best is yet to come. If you gently dig down, you will find that the caterpillarclub ends in what sometimes, at first glance, looks like a tuber but is actually the blackened remains of what was a larva or pupa of a moth or beetle. Suddenly and disturbingly, the ‘caterpillar’ bit of
its name becomes all too apparent.
Sometime last year, a microscopic spore (one of millions) was released from a similarlooking fruiting body. While many of its congeners were lost on the winds to fate, one got lucky and landed on a caterpillar. Once settled, it quickly sent out a growth known as an appressorium and, from that moment on, the caterpillar’s fate was sealed.
This pad of fungal life attaches itself firmly to the insect’s cuticle and then hardens and contracts, generating huge internal pressure. This in turn is used to force a penetrating root-like hypha out of a pore on its underside surface. By a combination of pressure and chemical action, the fungus rudely penetrates through even the toughest insect cuticle. Once inside, the spore withers away and the fungus gets on with the job of turning the caterpillar meat into mushroom.
A blastospore (asexual spore) forms inside the host’s body and the living net of mycelia ( fine white filaments) slowly ramifies through the host’s tissues.
With further investigation of Cordyceps, it is possible to find individuals protruding from both caterpillar and pupa, but the outcome is ultimately the same. It is ‘game over’ for the caterpillar, which eventually dies, after what is presumably a very slow and lingering demise, its critical organs now consumed by the last stages of the fungus, but not before it has crawled off to pupate in the soil. At this point, the Cordyceps looks like a tangled ball of microscopic knitting – a dense mass called an endosclerotium, a form that sees it through the winter. Here, it waits until late summer or autumn, when conditions for sporing are optimum, and around it goes again.