Best time to see: Mar to end Oct

Key facts

Blue- and green-bottles are the commonest of Britain's blowflies, breeding in carrion they often carry diseases

Thousands of their larvae, commonly known as maggots, can develop in a single carcass such as a rat or mouse

Commonest in summer but can also come out of hibernation and fly around on warm winter days

Recognition

Chunky flies with metallic blue bodies, red eyes and clear wings; bluebottles 10–14 mm long, greenbottles 8–10mm

Suck liquids from decaying matter and sometimes from berries with their mop-like mouthparts

Lifecycle

Females lay their eggs on decaying animals and faeces, attracted from considerable distances by the smell

The eggs hatch very quickly and the larvae burrow down into food, growing to full size within a week

The larvae leave the food and hide themselves away to pupate, the adult fly emerging a week or so later