Someone new on the acre

June has touched some wild nerve in the herb garden, so that comfrey, valerian, mullein, clary, have rushed up into shoulder-high thickets of bloom. Somewhere near the centre, Old Meg's cobbled grave is so muffled in catmint (a joke she'll have to forgive) that even the audacious swerves of her successor, skidding round the marjoram, are unlikely to disturb her.

Young Meg (no relation; just a name we're used to) is having a rapturous summer: a city orphan in a dog's paradise. Six months ago, she was one of a shivering litter rescued from behind a windy rock on Galway seafront: now here she is, leaping after butterflies and mashing them to bits on the grass.

As to the breed of dog she is, product of miscegenation and street-corner rape, the genes are still sorting themselves out. Spaniel mother, black labrador sire, but oddly scaled down and refined to something small enough to hug. Satiny black, white jabot, acceleration 0-60 mph in 3 secs; aka Black Lightning.

A grumpy old sod like me needs a dog; I'm tactile, like an eel or an earwig, and thrive on touchy-feely reassurance. My wife's too busy for curling up under my desk, warm muzzle on my foot; and unremitting adoration and fingerlicking aren't her form (nor was cleaning up puppy-shit from unexpected corners: "She's your dog!" - but now, of course, ours).

Meg Two had to have lively eyes: how awful it must be to own a dog one secretly thinks is stupid (or vice versa). In his book, In The Company Of Animals (1986), James Serpell asserted that a dog stared at directly by its owner will react differently from a cat, glancing away at frequent intervals, which can make it look sly or guilty. Dogs can swivel their eyes, like people, whereas a cat's eyeball is less mobile: to break off a glance it has to shut its eyes or turn its head away. Meg lies on my chest in bed, meeting my gaze in an unwavering frown of interrogation; eventually, it's my own nerve that fails (those incredibly white teeth!). But something does pass in these intimate communions, if only a reaching out to another consciousness. With the same intense scrutiny she explores the acre, sometimes pointing, paw raised, above a beetle or a spider. The other day, caught by her stillness and concentration, I found a life-and-death battle in progress in some long grass. A carnivorous ground beetle larva, no bigger than an earwig, had fastened on the throat of a large earthworm, which was trying to fling it off. It eventually succeeded in scraping free by backing into its burrow: a near thing. By such shared moments (between weeding and transplanting) Meg draws me into that busy world at the earth's surface - the insect metropolis that the French film, Microcosmos, explored so stunningly. She also maps the invisible web of scent-trails left by hedgehogs, trespassing cats and dogs, the badger that scars the lawn in its rummaging after grubs. Some of these trails end at holes in hedges I had never noticed before and they have taken Meg into a shadowy labyrinth where the blackbirds and dunnocks have their nests. There has been a great deal of screeching and, once, a limp and long-dead fledgling, carried up to me with an absent sort of tenderness. Meg's exercise of ferocity has been reserved mostly to pantomimes indoors, in the safety of the den. Anticipating her need to chew, I awarded her a pair of old, sweaty trainers on the first day home.

She spent weeks at tearing them to tiny shreds, bearing them aloft from room to room, hurling them about and leaping upon them with alarming growls and snarls. Since they finally disintegrated, she has augmented them from outdoors: twigs and lumps of fuchsia branch the size of ox-bones are sneaked into my study, chewed steadily to splinters in the lair beneath my desk. My feet rest in a raven's nest, refurbished daily. Is it just luck that she has never damaged anything I care about? James Serpell tells of domestic disasters when dogs, left alone, yield to "separation distress" by amputating chair-legs and disembowelling sofas. Perhaps their indoor urban world is also too tidy and sterile, too insupportably familiar. Out walking with me, Meg has chosen to carry unspeakable substances in her mouth - cow-dung, sheep-droppings, rancid silage dropped from a tractor. What these have in common is fermentation and decay. A dog can smell vinegar at one millionth of the concentration that humans can detect - a scent that might, indeed, be drifting from a dead caribou, 10 miles away across the prairie. Is it disillusioning to know that the leaping "kiss" a young dog bestows is a lick at the jaw of the returning mother wolf, begging her for regurgitated meat? Or that rolling on her back "to have her tummy rubbed", Meg is really soliciting a warm and cleansing lick of her ano-genital anatomy? Not at all: we draw comfort from a mutual fantasy of kinship. Dogs themselves are man's invention, a spiralling, proliferating, out-of-control experiment in genetic engineering. What a miracle that in all the hybrids within the species, all the shapes and colours and tail-lengths, there should survive the wolf's habits of constancy and love.

W H.Auden said a lot of what having a dog is about: "The single creature leads a partial life,/Man by his mind, and by his nose the hound;/He needs the deep emotions I can give,/I scent in him a vaster hunting ground."