A pile of wonder

By Richard Fortey

In the Chiltern Hills, 40 miles west of London, the morning mists disperse slowly in the still-damp days of early summer. But that does not deter the rider who daily trots her horse along the tracks that run through the stately beech woods. Silvery, undivided trunks rise like columns lining the nave of a natural cathedral. Wisps weave through them.

The bluebells that carpeted the woodland floor a week ago are already fading to a blowsy hue, and within a month will have vanished completely until next spring. The leaves on the beech trees are freshly unfurled, so that the roof of the woodland is still a bright yellowish-green. As the summer days lengthen, the leaves will darken, eventually capturing nearly all the sunlight until the forest floor becomes dark and uncongenial for flowers, and then home only to a handful of tough ferns. But for just a few weeks, a subtle and penetrative illumination will encourage the horsewoman on her way.

Then her horse stops abruptly to deposit a mound of manure in the grass along the path. It steams gently in the moist air. How many of the passing dog-walkers know that this dung provides the cradle for a wonderful, tiny organism: the hat-thrower fungus, Pilobolus?

The release of the dung stimulates the germination of minute spores that have passed unchanged through the digestive tract of the horse. The dung needs only to be kept damp, which it will be in the shade of the woodland ride. The rich manure becomes penetrated by microscopic threads which feed the fungus. In a matter of days, a kind of fuzziness obscures the surface of the droppings. Tiny, translucent filaments decked in dew beads rise from all over the dung, seeking the light. They swell at their tips into a series of watery balloons. Then black, spherical spore packages—hats—develop on top of the threads, containing the seeds for future generations. All this happens at a scale of less than two inches, so, to the passing walker, it might seem only that the dung has been covered in a dense, fine spider’s mesh.

The climax of the drama comes when the droplets beneath the dark caps reach a critical size and burst. The black spore packages are shot as if from a cannon, away from the dung and towards the light and the surrounding vegetation—hence the nickname “hat thrower”. In a trice they generate an extraordinary acceleration of 20,000g. They can travel for more than a yard; for their size, they are global record-breakers.

The spore packages are even equipped with a special glue to help them stick to blades of grass. To the untrained eye, they may look like specks of black pepper. There they remain, awaiting the attention of another grazing or browsing animal. Once consumed, they re-enter the herbivore digestive system and the cycle starts afresh.

The secrets of small living things like the hat-thrower fungus are every bit as wonderful as those of elephants or eagles. And if you don’t fancy being caught in the woods staring closely at a pile of excrement, you can always collect some damp dung and put it in a Tupperware box, sealed with a lid. If you leave it for a few days, all you will need to enjoy the spectacle is a magnifying glass.

Or maybe it’s better to leave the little fungus to its job, quietly recycling animal waste, as it has for millennia. Were it not for the work of many such small and overlooked labourers, our landscape would be despoiled with waste. I take my hat off to them.■

Image: Science Photo Library