This is the largest and most spectacular ichneumon I see in my garden, Pimpla sp. They are parasitoids of moth caterpillars. The females walk jerkily over the vegetation, constantly tapping the surface of leaves with their twitchy antennae searching for caterpillars. Once they find a suitable host, they use their dagger-like ovipositor to hypodermically inject the caterpillar with an egg, which will develop into the wasp larvae. The larvae feeds on the caterpillar's organs and kills it before emerging like an adult wasp. There are over a thousand ichneumon species in the UK, and they are often difficult to determine without microscopic examination. They are also quite tricky to photograph due to their nervous disposition, so I cooled this one in the fridge for 20 minutes before photographing, and it only took a couple of minutes to fly away!