Shield bug

Red-legged shieldbugs Pentatoma rufipes are very numerous hereabouts at the moment, often sunning themselves on oak leaves.

Shieldbugs generally feed on plant sap by piercing leaf veins with their pointed mouthparts, though they will also eat slow-moving animal prey like caterpillars.

This one had taken a liking to feeding on a bird dropping, which is likely to be a good source of minerals. Many insects, including butterflies, will eat animal excrement as a source of calcium that they need for egg laying.

The grey patch just above the middle leg here is the site of the stink gland, which produces a nauseating fluid that deters predators.

The Field Studies Council publishes this excellent fold-out identification chart of shieldbugs. They're an interesting group to study because a) they aren't difficult to identify b) there aren't too many species, and c) they are quite slow-moving, so they are easy to watch and photograph.

There is also an excellent web site called British Bugs devoted to all the hemipterans, including shield bugs, which can be accessed by clicking here.