Apologies to William Blake and the world in a grain of sand and all that.

Today, being a May Bank Holiday Weekend, it is very sunny and bright but the temperature has plummeted. I went shopping with my bicycle — wearing a thick fleece under a windproof jacket, and a ‘silk’ balaclava under my cycle helmet. So much for ‘Cast Ne’er a Clout / Till May be Out’. (I’ve never been sure whether ‘out’ means ‘May has come out’, i.e. it has begun, or ‘May has gone out’, i.e. it has ended. Whichever, it’s remarkably cold.)

After all the nature reserve visits lately, it’s time to look for wildlife closer to home. The blue tits have a lot of hungry little mouths to feed in the nest box above the kitchen door, and the adults flit in and out every minute or two. Sometimes one parent is still feeding when the other returns, whereupon the returner goes and perches in the Apple tree, calling softly, until the feeder flies out. There must be at least 40 feeding trips per hour, and it could easily be more. Remember that next time you’re wondering how much trouble kids are.

The Blackcurrants are in full leaf now, and suddenly today each leaf seems to have an insect crawling over or displaying upon its upper surface. Some are certainly brief visits: smallish Ichneumon flies, about 10mm long and very slender, walk or run hastily about, on the lookout for caterpillars to parasitise with their eggs, a way of life disgustingly cruel enough to put Charles Darwin off religion for ever – leaving all the intellectual arguments aside, he simply found it sickening to imagine a loving creator doing anything so cruel. It’s interesting for such a careful scientist, able to spend 20 years marshalling arguments and evidence, that on a personal level, it was a visceral reaction that settled matters.

Other insects are clearly more like residents. Half-a-dozen leaves have a boldly coloured Harlequin Ladybird (or two: mating) in full view. It has been well said that insects fall into two camps: those that take good care not to be seen, and those that make sure they can be seen. Ladybirds, with their bold warning colours – red+black, yellow+black, red+black+white – are certainly in the conspicuous camp. This means they are signalling their unsuitability as food; the great pioneering zoologist E. B. Poulton coined the term ‘Aposematism’ (Greek ‘apo’ = from, ‘sema’ = sign, i.e. ‘warning off’) for this kind of warning coloration. In the case of the ladybird, they have bitter, foul-tasting or toxic chemicals in their bodies sufficient to make any predator gag, spit them out, and remember not to eat them again. This doesn’t necessarily save the life of the one they learn on, but it’s good for all the others. Each foul-tasting animal gets a better chance of not being tried out as a meal if it looks as much like other foul-tasting animals that predators may have had a bad experience with already. The result is Müllerian Mimicry (yeah, another famous Victorian zoologist) in which the vile imitate the vile as closely as possible. This is why bees look like wasps which look like bees: they all do better if they have the same obvious ‘don’t mess with me’ look.

The Harlequin Ladybird is big and bold, advertising itself fearlessly. It is spreading rapidly through Britain, having been unknown here not many years ago. It hasn’t totally displaced our native ladybirds: in fact, my Blackcurrant bush is also home to several 2-spot Ladybirds, much smaller and red all over but for one big black spot on each wingcase. The Harlequins are so called because they have many possible patterns, from much like a 12-spot Ladybird to almost entirely black (the odd red patch remaining), but they always have quite a lot of white on the head, which the natives generally don’t.

As if that wasn’t enough, several small rather triangular true flies (Diptera) are displaying on the same bush; these are probably males waiting for a mate. They lack the ‘pictured’ wings of the Celery Fly – I’ve got those too, worse luck, though they are pretty little insects, and it’s curious to see them in a mating pile-up, as rival males fight to get the female. What she thinks of it, nature does not relate.

All you have to do to enjoy diverse insect life in your garden is … not to spray. In fact, the insects I’ve seen today are a good reason why spraying is a bad idea. The ladybird larvae are powerful predators of aphids, while the Ichneumon ‘flies’ (parasitic wasps) are valuable biological controls of many damaging species of moth, killing their caterpillar larvae. In short, they are the gardener’s friends.

That’s a lot of the world on a leaf. Or at least, a lot of evolutionary ecology for a May Bank Holiday weekend.