Country diary: Sandy, Bedfordshire

A spider on a web in a sunny garden.
Spiders are hunted and stung with devastating speed by the spider-wasp. Photograph: Graham Turner for the Guardian Graham Turner/Guardian

A grasshopper-green insect sprang up from under my feet and over the open heath. It did not leap and land but drifted some distance before coming to earth. The green tiger beetle enticed and eluded. Although it is a ground predator of some beauty, its lime shell inlaid with cream and white studs, it is apt to fly when a human bears down on it. I tried to follow its course, but lost it and soon became distracted by tiny movements behind a single sprig of heather, where little jets of sand spurted out of a pencil-thick hole.

After a moment, the digger stopped excavation and left its burrow, pattering over the soil with purposeful randomness, darting this way and that. This insect was hard to label; first impressions were of an elongated fly just under 2cm long, with a bulbous head, a black metallic body and Day-Glo scarlet strips on its abdomen. Its legs were not splayed fly-like to the sides, though, but held crooked at the joints like those of a wasp. Most striking were the transparent wings, closed over the body, but continually flicking up and down as if the pumping action powered the creature along.

It paused at a piece of debris and tossed it aside so fast I could not tell if it used its jaws, feelers or forelegs. Turning over an old leaf, it had hoped to surprise a wolf spider in its lair, but there was nobody home. Had there been, the spider-wasp Anoplius viaticus – for this was she – would have whipped her abdomen round with devastating speed to sting the spider. Then she'd have dragged the paralysed creature back to her newly excavated burrow.

Today I have returned to exactly the same spot to look beyond the same sprig of heather. There is an even, sandy surface where yesterday there was a hole. Just beneath, an immobilised but still living spider shares a nursery chamber with a single egg. In a few weeks' time, the surface will crack open and a well-fed adult spider-wasp will emerge.