If you go down to the woods today, unless you've got very sharp eyes, you may not notice anything surprising.

But look down and on the forest floor you might see tiny white popcorn-shaped objects poking up out of the leaf litter.

Easily overlooked, these are fungal headstones marking the graves of unfortunate young cicadas.

We're all familiar with noisy cicadas appearing over summer, but for most of their life they live underground.

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BENEATH THE GROUND: The fungus can be traced down to the bodies of parasitised cicada, several centimetres underground.
BENEATH THE GROUND: The fungus can be traced down to the bodies of parasitised cicada, several centimetres underground.

The cicada nymph is a pale wingless creature that has a subterranean existence, sucking sap from tree roots. After at least three years it emerges to become a short-lived winged adult. Although the underground life might seem safe and sheltered, a cicada nymph faces one danger - fungal infection.

The fungus in question, Isaria sinclairii, infects cicadas and other burrowing insects. It eventually kills and consumes them completely from the inside out, leaving just a few bits of exoskeleton marking the outline of the nymph.

In a particularly rainy summer, like the one we've just had, the fungus will then send up a fruiting body that protrudes maybe a centimetre above the forest floor.

Looking rather like tiny popcorn on a stalk, it smears anything it touches with dusty white spores, which grow into pale fungal threads in the soil until they encounter an unfortunate insect.

A close relative of Isaria is Ophiocordyceps robertsii, the so-called "vegetable caterpillar" (poorly named, because a fungus is neither animal nor vegetable).

This species infects the large caterpillars of the forest ghost moth (Aoraia enysii) which live in the leaf litter; its fruiting body resembles a brown spike.

The parasitised caterpillars, called awheto, were eaten by Maori and when dried and ground up made a bluish-black dye for moko. Awheto are often dug up as curios, and the museum has several in its collection.

A fungus that infects insects might seem like just a curiosity, another odd story about the web of life that makes up the forest.

ALL THAT REMAINS: Although the bodies of the cicada have been completely consumed by fungus, some of their exoskeleton persists to show they were once insects.
ALL THAT REMAINS: Although the bodies of the cicada have been completely consumed by fungus, some of their exoskeleton persists to show they were once insects.

But it's more than that.

In the 1990s Japanese scientists examining different fungal species for their possible medicinal uses cultured Isaria sinclairii in the lab, and managed to extract a chemical from it that acted as a powerful suppressant on the human immune system.

This is a big deal, because autoimmune diseases like multiple sclerosis affect millions of people around the world. A synthetic version of the chemical they extracted, named fingolimod, has now been approved as a multiple sclerosis treatment, and it may turn out to be useful for treating cancer as well.

When we talk about preserving biodiversity, most people tend to be quite self-centred. We like forests and pretty birds, and are willing to spend conservation dollars preserving them, but draw the line at saving insects, or leeches, or obscure little fungi.

Conservationists often argue that all living things have some right to existence, regardless of whether they're valued by human beings or not.

But another argument is to point to the obscure cicada-killing fungus Isaria, which turned out to contain a treatment for a disease that afflicts millions. What other wonders lurk undiscovered in the New Zealand bush, amongst species overlooked, or on the verge of extinction?

Mike Dickison is curator of Natural History at the Whanganui Regional Museum.