I love to see oak branches and twigs in winter. They are all dark elbows and angles against the sky, quite at odds with the elegant or sweeping lines of beech and ash. I love to feel oak’s thick and coarsely ribbed grey bark, so emphatic compared with the gentle surface of beech. Our species is the pedunculate, or English oak (Quercus robur)—heart of oak itself—and the finer of our two trees is probably about eighty years old, the same age as several of our more mature beeches. Its trunk rises sheer and straight among its beechen neighbours. In spring, oak leaves appear later than on nearly all the beech trees, but they are all so far up that I only receive occasional messages from on high to keep up with the oak’s progress. Oak catkins are little more than strings of stamens, and when they fall to the ground in May they are a slightly sorry sight, like threadbare mouse tails. Wind-blown oak leaves tumble down from time to time. Some of them display spangle galls on their undersides—pink-flushed discs that look like tiny press-studs applied to the leaf surface. They are produced from the leaf after stimulation by chemicals secreted by a minute gall wasp with a long name: Neuroterus quercusbaccinum. Something like five hundred invertebrate species are supported by oak trees, more than any other forest tree, so the canopy must be thronging with insect life if only I could reach it. Tannins are supposed to offer the tree some protection by making its leaves more unpalatable, but plenty of animals have evidently found a way to cope with this distraction.
This year is a good one for the acorns that now lie scattered all over the ground under the tree. It is a “mast year”—something that happens about one year in five. Long ago, wild boar would have feasted on the fallen acorns, and medieval swineherds would have fattened up their pigs on the back of their brief profusion, but many years have passed since rights of pannage were taken up for the wood.8 Nowadays, the abundant yield in a mast year is under-utilised. Many of the acorns still sit in their scaly cupules, which hold them as snugly as eggcups supporting eggs. I take out one acorn, which leaves me holding the cupule, and the stem on which it sits—the peduncle that gives the English oak its Latin name. As a child I often put this little contraption into my mouth as a pretend pipe. It feels so small now. This oak could see a dozen of my lifetimes and still have many good mast years ahead of it. I put that profound inevitability into my pretend pipe and pretend to smoke it.
Some of the acorns are still green, but most have faded to tan; yet here is something that is not an acorn, though not so dissimilar in size. Perfectly spherical, and polished brown, this marble gall was produced as the tree reacted to another tiny wasp, Andricus kollari. This specimen is for the collection. I can see the wasp’s tiny exit holes from the safe house full of food that it persuaded the tree to make for it. I have never seen the wasp itself, which is not surprising, since it is only two millimetres long. Oaks support more species of gall wasps than any other tree, and each species stimulates a gall with a highly specific shape. It is a wonder how the tree “knows” to do this, and I am not clear how one shape rather than another fits in with the life of a particular wasp species. Dryads were Greek nymphs as specific as a gall wasp to the oak tree; maybe they would have been able to tell me the answer.
Oak trees became an important part of the economy from medieval times. Within the Greys Court estate the old woodward would have known trees as individuals. He would have understood when to leave well alone and when to harvest. Now the estate has passed from the hands of lords of the manor—the woods sold off, the old house and grounds run by the National Trust and managed for visitors. The stewards of what is now an Oxfordshire “day out” look to the danger to the public from falling trees rather than to profits from tanning or pannage. The oak, however, remains in charge. The National Trust logo is a stylised oak sprig: four leaves, one acorn, a few cupules. What else? After all, oak is somehow “national” (“heart of oak…”); and “trust”—like honesty, durability and stalwartness—is another of those words that attaches to oak like a gall.
Truffles
I am crouched under a beech tree a little way from where its main roots are anchored into the thin soil. In my right hand I have a tiny rake bought from a toy shop. I have noticed little diggings into the beech litter around this particular tree. I set about scuffling under the surface with my slightly comical implement. In a few moments I have scraped away some of the loose leaves and have got down to something like soil and rotting litter. It is so stony that I have to remove flints as they get in the way, but quite soon I see slightly puffy pinkish rootlets belonging to my beech tree—they branch profusely like little trees themselves. I know that these are roots with mycorrhiza (this page) on the outside. Beechnuts seem to have hidden themselves perversely in the ground to resemble tiny truffles—after all, they are brown, bean-shaped, and buried. I carry on with a little less enthusiasm than when I started, since I have already failed several times in my search. Then the rake brings up something different: rounded bodies looking like rusty-brown rabbit-droppings, as large as big peas. I have struck lucky at last. Under my hand lens I observe that the little objects have a typically warty surface. After looking for so long I have recovered four truffles in as many minutes.
When truffles are mentioned, most people begin to salivate and put on a mental bib and tucker. They think of the celebrated black truffe de Périgord, or of the most expensive foodstuff in the world, the white truffle of Italy, the Château Petrus of the gastronomic milieu, weight for weight more valuable than gold. They seem disappointed when confronted with four rabbit-droppings. Most truffles are modest objects of this kind. There are numerous species, but since all of them develop underground they are unfamiliar even to experienced naturalists. They have to be hunted down. I was taught the routine by Caroline Hobart, doyenne of English trufflers, whose customary post on a fungus foray is underneath a spreading tree with a blanket to sit on, and a small rake to scrape with, and a collecting box to house her finds. It is more like archaeology than mushrooming.
I know the particular truffle species I have just discovered—one of the common ones, Elaphomyces muricatus. When cut through, the interior of a truffle usually has the consistency of hard cheese, and has a characteristically marbled appearance, although the general ground colour can vary. When first dug up, truffles can resemble potatoes, or cape gooseberries, or snowberries, or rabbit-droppings. In truth, a truffle is not a particular thing at all: it is a habit. Let me explain. Several groups of fungi have discovered the advantage of growing to maturity without breaking above ground. Their spores develop within a sack-like fruit body. Most of these species are spread by animal activity—especially grubbers like wild pigs—and to help this process they evolved the most delicious smells. These wondrous odours are fugacious; an old truffle does not smell of all kinds of lip-smacking meaty umami rolled into one, but just rather stale. (Beware all cheap-truffle vendors, for they are selling a half-remembered dream.) The spores pass unharmed through the digestive system of the animal and are spread through the wood.
It has been known for a long time that truffles arose from the two major groups of larger fungi. Some truffles are related to honest-to-goodness “shop” mushrooms (Basidiomycetes), while others are closer to morels (Ascomycetes)—so they had entirely separate evolutionary origins.9 All the delicious ones belong to the second group (my species was also an “asco,” but not one of the good ones). This phenomenon of similar form evolving in response to similar adaptations is common in nature, and I am glad to have it demonstrated in the wood—it is often called “convergence.” What was not fully realised until the molecular age was that the truffle habit had evolved separately even within the two major groups. Many different fungi wanted to have a go, as it were, at being a truffle. Sequences obtained from genes extracted from the DNA of the truffles have identified their closest relatives among several, only remotely related, kinds of fungi. This means that rather similar-looking truffles are now included in the same classification alongside very different-looking mushrooms, proving again that ev
olution can cheat common sense. All truffles seem to be associated with tree roots in a mycorrhizal relationship, so they donate useful nutrients to the tree in return for sugars derived from photosynthesis. By maturing underground (hypogeal habit) truffles avoid the perils of spore dispersal in air, where fruiting bodies are always at risk of desiccation. The spores go straight into an efficient dispersal mechanism—otherwise known as a digestive tract. It works very well for the fungus, and equally well for the trees that are partnered by the fungus, which receive a home delivery of the right collaborator gift-wrapped in a parcel of dung. It is the kind of adaptive package upon which evolution really likes to get to work—hence the recurrent truffle habit.
I wish I could say that I had discovered truffles in the wood by spotting the tiny truffle flies (Suillia pallida) that hang around the location of buried mycological treasure like bloodhounds round a corpse in a shallow grave. Trufflers have claimed to be able to master this entomological trick, and I almost believe them. The summer truffle (Tuber aestivum) is our native edible species, and I would dearly love to find it in the wood, with or without the help of flies. My lesser discovery was prompted not by any insect, but by a series of blatant scrapes down into the litter. I wondered about a badger on the prowl, but the size was probably more appropriate for squirrel activity. Nothing with olfactory organs can resist the lure of a truffle, even if it means coming down from the safety of the trees.
The Fly Man Cometh
I am ignorant when it comes to flies, and not just truffle flies; but then, there are an astounding number of flies to be ignorant about. I need help. I worked alongside Dick Vane-Wright for several decades at the Natural History Museum—or, to be more accurate, his office was about half a mile away from mine in that great warren of a building, but we both knew its secret ways. Dick has an unquenchable enthusiasm for crane flies, and he is making one of his visits to the wood in search of them. Flies have two wings to fly with rather than four—hence the name of the insect order to which they belong: Diptera (true flies: “two wings” in Greek). The second pair of wings in flies is modified to become distinctive balancing organs. Fly experts are known as dipterists.
Dick will have to stand in for several dipterists, each with their own favourite kinds of flies, who came to Grim’s Dyke Wood to use the cherry-picker. The antics of collectors in acquiring their samples are not dissimilar. Crane flies (“daddy longlegs” to some) will lead the show, because they are the largest of the fly persuasion. With their spindly legs and long, skinny wings, they are a familiar sight just this month, bumbling and blundering around meadows, shedding limbs. Dick himself has a certain leggy presence: tall and gangly, with beard and straggling wispy white locks, he bears an increasing resemblance to Gandalf. It is a warm, slightly humid day—a good one for flies. Dick arrives with a net, and not a particularly discreet one; in fact, it resembles a rather voluminous pair of white Victorian bloomers mounted on a stick. To bring up the crane flies he prances up and down in the vegetation by the path, at the same time making broad sweeps and lunges with the net. A dog-walker passes by, and the dog looks even more astonished than his owner at the goings-on. He (the dog) cannot bring himself to bark. For the smaller insects, there is a short pause to suck out the catch from the base of the net into a collecting jar using a “pooter,” but the larger crane flies are popped directly into a killer jar. They have to be taken away and studied under a binocular microscope to be accurately identified.
So what is the problem? A crane fly is just a crane fly, surely? Absolutely not! The challenge is that there are more kinds of crane flies than there are species of birds. Six hundred and eighty-eight genera of crane flies have been recognised, before you pass on to the 15,391 named species; and remember that previously unnamed new species are still being discovered every year. Just over three hundred species are known from Great Britain. There are actually very few people who can identify crane flies with confidence. With the exception of most of the Lepidoptera (butterflies and moths), this is the problem with many kinds of insects, and is the reason why the list of species from Grim’s Dyke Wood is still incomplete. The crane flies are just one family group within the true flies, and there are over a hundred more families.
For most of them, I await the right expert. However, the crane flies have one extraordinary advantage: Charles P. Alexander (1889–1981). He is not as well known as John James Audubon, maestro of the birds, let alone Charles Darwin, the naturalist’s naturalist. In the annals of crane flies, however, he reigns supreme. Alexander scientifically named and described no fewer than 11,278 species, one for almost every day of his career. Two-thirds of all crane flies were named by him, and he published 1,054 scientific papers, which may be a world record. I don’t imagine he had much of a social life. There are invertebrate species waiting to be discovered in every part of the world, from tropical rainforest to deep oceans, and probably even in our wood. Scientists disagree on just what proportion of all species we already know, but even the most conservative taxonomist would accept that we currently recognise under half of the world’s biodiversity.10 To those who say that the task of collecting and describing this vast inventory of unknown species is impossible, simply too overwhelming, there is one unanswerable riposte: Charles P. Alexander.
The rituals of identification become second nature to an entomologist. One specialist might focus on colour patterns, another on mouthparts, according to the type of insect concerned, but I believe that almost all authorities are interested in genitalia. On reflection, almost everyone I know is interested in genitalia. The wings of flying insects such as crane flies are supported by a series of struts known as veins, and are further divided into compartments called “cells.” These display great constancy within a group, and vary from one group to another, which is meat and drink to an entomologist. The sexes of crane flies differ. The male of one of our wood species has gorgeously fluffy antennae, for example, in comparison with a less endowed female. Colour spots appear on the wings of other species; legs can get stripy. As for the genitalia at the tip of the long abdomen, they comprise a complex, whiskery sort of arrangement that you would have to be an entomologist to know and love. They are of crucial importance to the insect—not least to ensure that the right partner is mated—which makes them equally of interest to Dick Vane-Wright.
A common crane fly recovered from the wood, Tipula oleracea, was named by the great Linnaeus in 1758, and so is twinned with our beech trees in scientific history. It could even be claimed that this species, by historical precedence, is the daddy of all daddy longlegs. Its larva is an unlovely brown grub known as a leatherjacket, which causes serious damage to roots of garden plants and is loathed by horticulturalists, although much appreciated by hungry birds. Dick provided me with a set of detailed notes on the other fifteen species of crane flies recovered from the wood. His descriptions have an esoteric poetic quality when he describes “the slightly infumed area of the more posterior wing membrane,” or a “maculated wing pattern,” or maybe “exquisite bipectinate antennae.” This is the love of a naturalist for his very own bugs.
Yet I had been bugged by a question myself: I wondered how the wood could support so many different species of crane flies. Now I know. Their leatherjackets have specialised preferences, and mature at different times of year. Tricyphona immaculata likes the soggy conifer woodpile at the edge of the track; Rhiphidia maculata prefers rotting beech elsewhere in the wood, and emerges after Ormosia lineata in the same habitat. A common species with pretty, spotted wings, Limonia nubeculosa, is more of a generalist, or an “opportunistic facultative xylophage,” as Dick succinctly, if technically, puts it; Cheilotrichia cinerascens was collected around holly; Erioptera lutea lives in soil. The larvae of Ula mixta are fungivores, probably feeding on decaying bracket fungi. This particular species was only named in 1983, and might have been considered a rarity until recently, but it is more likely that there was just nobody around to recognise it for what it was. The largest crane
fly of all was Tipula maxima, with mottled wings, whose larva lives in damp soil—possibly from the permanently moist area along the track. However, the most spectacular species is coloured up all black and yellow along the body like a thin wasp: Ctenophora flaveolata. Its comb-like antennae resemble the artificial eyelashes of a 1950s femme fatale. It is not at all common. “A nice beast to find,” says Dick. Its last recorded occurrence in Oxfordshire in 1993 was thought worthy of a note in the British Journal of Entomology and Natural History; it was from the Warburg Reserve, two and a half miles north of us: “a species of ancient beech woods,” remarked its discoverer.
Details, details, you might protest. I reply that the delight, as well as the devil, is in the details. To an animal of small size, particularly an insect in which the larva hides away discreetly to feed and grow, our wood is a potpourri of opportunities, quite a wonderland of niches. “Biodiversity” as a word sounds rather dull and a bit abstract. Played out on the ground it is something else: the difference between the numbered title of a symphony and its glorious complexity unwrapped in a concert hall. Every rotting log is a small world. The underside of a leaf is a realm to a greenfly; a crack in the bark of a beech tree is a capacious and secret hideout. They all fit together in a jigsaw that remakes its own pieces month by month. Crane flies emerge only briefly into the common democracy of the air to meet their mates and continue the species; otherwise, they are sequestered in secret places, biding their time…A late sunbeam cuts across the clearing, and picks out all the flying insects as dancing motes. Each little life is not much more than a pinhead of brilliance. Some bob up and down together; a mating dance, I suppose. Others move purposefully and then vanish from the light, seeking something, smelling something, following a precise instinct to a precise niche. Even if I had the scientific names of them all, it would only be like having the notes on a page, not the symphony. A species inventory is only the beginning. Every species will have its own biography, its special requirements and its curious secrets. Dick tells me that the early stages of some of the crane flies in our wood are still not known. How much more is there still to find out about the hundreds of insects adrift in this aerial confetti?
The Wood for the Trees Page 16