You wouldn’t think that you might start to grasp the immense diversity of life on earth in a small river running through a Dorset village; but you can. That is, if you start to realise what’s under the water surface.
The river in our village isn’t hugely visible, in fact it’s somewhat tucked away—it isn’t like the Sydling Water, say, which you can’t miss as it flows so charmingly around the cottages in Sydling St Nicholas—but once you know where to find it, you are struck by what a beautiful watercourse it is, a chalk stream of crystal clarity. And it has a group of conservation-minded villagers who are its active defenders. Every month, in the spring and summer, on the alert for an early warning of pollution (which would mean informing the Environment Agency) they monitor the river’s condition by testing the level of its aquatic life.
They do it by taking what are known as kick samples—you kick and scrunch the riverbed vigorously with your boot, holding a net just downstream, and see what flows into it. What they’re looking for are mainly the larvae of aquatic flies, such as the mayflies which fly fishermen imitate with their artificial creations, to attract trout.
Using them as health indicators is a procedure devised by anglers, in fact, known as the Riverfly Monitoring Initiative, although it has spread beyond the angling community, and Angus Menzies of the Dorset Wildlife Trust will train non-anglers to do it. Such are Roy, Robin, John and Prue, and Pauline who do it in our village, where the river flows through the garden of our friend Kate, and is thus easily accessible (Kate generously provides coffee as well as access). For the last few months I have been watching them, and in doing so, my eyes have been properly opened to the true nature of life in a river.
For if you ask people about this, I think many would just say, fish. That’s understandable. Fish are familiar—you know what a trout looks like, don’t you?—and if we peer into the water, sometimes we can see them. People might also instance otters and water voles as examples of river life, and maybe herons and kingfishers, which are similarly visible. Yet all these creatures are vertebrates, that is, animals with backbones, and taken as a whole they represent only a tiny fraction of riverine biodiversity. It is the invertebrates, the small backboneless animals, the insects, the snails, the crustaceans, the molluscs, the worms and all the other bug-like things, which make up the vast majority of river life—it’s just that we hardly ever see them.
But they’re what Roy and his fellow monitors are looking for. To be precise, they’re looking for eight invertebrate species, seven of them insects: four mayfly larvae, two caddisfly larvae, and a stonefly larva (the eighth species is a crustacean, a freshwater shrimp.) These have all been carefully chosen for their sensitivity to pollution—if they’re present in good numbers, the river is likely to be healthy—and also for the fact that they can be identified by non-specialists, so making possible yet another example of the citizen science which is at least one thing in Britain we do inspiringly well.
And watching our monitors do their kick samples and sort out the contents of the net, from a bucket, to a tray, then to a compartmentalised tray, you get a remarkable vision of teeming life. I had never realised there were just so many different small living things in the fronds of the water crowfoot and the gravel of the river bed—not just the mayflies and caddisflies and stoneflies and shrimps, but beetles and mites and snails and leeches and damselfly larvae and so much more, in a wonderful abundance of the sort we used to have on land, in the countryside, before intensive farming destroyed it.
You won’t grasp this, the true miraculous diversity of life in rivers, and by extension of life on earth, by just counting the things you can see, such as fish: in Britain we have only about fifty freshwater fish species. But we have about 3,800 species of freshwater invertebrates, which may be generally invisible, yet whose amazing multiplicity I found myself comprehending, in watching Roy, Robin, John and Prue, and Pauline sorting through the wee beasties which emerged from our village’s small and lovely chalk stream – patient, all of them, enthusiastic and committed (and fortified by coffee from Kate.)
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