I found this splendid little chap in my garden. It’s an adult Hawthorn Shieldbug Acanthosoma haemorrhoidale a member of the Hemiptera an order of insects most often known as the true bugs. It will overwinter as an adult, often darkening before hibernation and will emerge again in the Spring.
The antennae in Hemiptera are typically five-segmented, although they can still be quite long, as can be seen in this photo.
Hemipterans have sucking/piercing mouthparts. The mandibles and maxillae are sheathed within a modified labium to form a ‘beak’ or ‘rostrum’ called a proboscis. This sharply pointed tube is capable of piercing plant tissues and is used to suck out the liquids – typically sap. When the proboscis is not being used it is folded flat against the underside of the body.
The young are called nymphs and resemble the adults to a degree although they are often mistaken as other insects.
Ashley Wood has produced a series of illustrations showing the life stages of a range of UK shield bugs, which is particularly useful for identifying the immature nymphs and the various instars.
Check it out here.