Snakes, wasps and spiders...Anna Pavord is enchanted and mystified by the residents of her garden

At last I've seen it, the snake that, over the past two seasons, has left perfect casts of itself in the garden. The skins, dry and crisp, were each about 130cm long, rounded like long sausages, each scale perfectly overlapped on the next. You could see where the eyes fitted in, where the mouth had been. They were light, translucent, fabulously beautiful things. But how could I have been sharing the garden with a creature four feet long and never seen it?

Then on a sunny evening a few weeks ago, I crossed the yard to the house. In one suspended moment, I saw the snake basking on the warm stones in front of the door. The moment didn't last long enough. With amazing speed, it slid under the gate and disappeared into some dry leaves. It went diagonally like an African sidewinder, which was a surprise.

I've replayed that moment often. I'm mad about snakes, but they've had a sad time with us humans and have every reason to keep themselves hidden. All of my best snake moments have been in South America, but they are as persecuted there as they are with us. The worst episode was at a so-called "eco-lodge" on a tributary of the Amazon. On our way by dugout canoe to this place, I'd had some mesmerising encounters with snakes, watching them twist through the water, then without missing a beat, climb straight up the trunk of a tree on the water's edge, brilliantly camouflaged in both elements. When I stepped out at the landing stage of the lodge, four of these beautiful creatures were hanging dead on a wire, pegged out like washing. "What happened?" I asked. "We kill all snakes," said the American manager. "The bird-watchers insist on it. They don't like them." We left on the next available dugout.

The snake in our garden is a grass snake, the biggest of British snakes, but completely harmless. It's a soft greyish-green, paler on the underside, dappled with black on top. How does it spend its days, I wonder? Where does it go? Grass snakes like ponds and marshes where they can get plenty of frogs. But we don't have a pond and the stream below in the valley is not ideal frog territory. We have good compost heaps though, which is where they like to lay their eggs.

I reckon I was lucky to get even my few seconds with the grass snake. In Complete British Animals (Collins paperback £14.99), Paul Sterry explains that they constantly taste the air with their forked tongues. The scents they pick up pass through filters in their mouths and this is how they build up a picture of what is going on around them, where possible prey might be. I bet the snake had smelt (or "tasted") me long before I saw him.

Perhaps now you are expecting me to give ten top tips for making a snake-friendly garden. Sorry. No. I don't share the general belief that we, as humans, are perfectly equipped to arrange the lives of other wild things. Plants, on their own, give me enough surprises. Animals are even more complicated to understand. And though I can learn all about the way a grass snake functions, its diet, its usual habitat, these are just bits, just facts. The vast, inter-related sequence of events that has kept it here these last two years, the big picture, is what matters. And this is never clear.

If we are interested in wildlife, it's likely to be one particular aspect of it: birds (probably), butterflies, the prettier things. Because we've separated ourselves away from the natural world, we separate other things too. But they, left to themselves, stitch themselves together into a woven whole. We're dangerous because we are arrogant enough to think that we understand its complexity.

Encounters in our garden with damselflies, stag beetles, woodpeckers, ravens, slow worms, elephant hawk moths, deer, badgers, toads give me great pleasure, but the best thing I can do for them is stay out of their way. What is the point of luring birds to a birdtable only to be killed by the neighbour's cat? But even if we can't understand what all these wild things are looking for, we can at least ensure a good spread of possibilities in our gardens.

Dead wood somewhere nearby must have persuaded the wasps to build a nest in the shed where our freezer lives. When I first noticed it, on the beam above the freezer, it was smaller than a bantam's egg. Now it's about the size of a celeriac, made from wood chewed up with saliva to make a kind of paper, laid down in beautifully modulated stripes of cream and buff.

It's a designer's dream, a gorgeous colour and shape, made in overlapping petals. But since the wasps started to build, an energetic spider has made a huge hammock web that stretches from the nest right across to the next beam. The wasps aren't as direct as, say, the swallows in the way they come and go from their headquarters, so quite often they get caught in the web.

They are strong enough to escape, but not without a lot of effort. Why, since they are clever enough, co-ordinated enough to build so beautifully, don't they send out a work party to cut the web away from the nest? Is there some benefit in having the spider close by? There's definitely a benefit to gardeners in having the wasps about, as they feed chewed-up insects to their young. Insects are critical for the swallows too, who for the last couple of years have chosen to nest on top of our electricity meter. For insects, you need oak trees. For oak trees you need deep, retentive soil. For the right soil you need a particular geology and climate. Lord! My head's swimming. I'm going weeding.