A bluebottle is a type of blowfly, a non-biting fly found all over the world. Except for their blue to purple-black metallic colouring and slightly larger size, adult bluebottles (Calliphora vomitoria) resemble houseflies. Bluebottles fill the niche of primary decomposers, for they break down dead matter and make use of what is otherwise unusable organic material.
Females lay their eggs on decomposing material such as fruit or a deceased animal. They are capable of locating and arriving at a corpse within a few hours of its death and are usually the first of many insects to make a meal of a decomposing animal. They prefer snug places inside cavities such as the nose, mouth, and ears where they can lay their eggs in a dark, moist environment.
The eggs hatch approximately twelve hours after they are laid, and the larvae feed on the decomposing material just as their mother did. Over the course of eleven to twenty days—longer in cold weather and faster in warm weather—the larvae eat and grow. They go through three larval stages, or “instars,” during this time. Instars are a method of larval growth in which the larvae moults its skin.
Once they’ve finished their larval period, the bluebottles begin pupation. They may pupate on the body if a suitable site is available, or they may move away from their food source, travelling several meters in order to burrow into the soil or under rocks and logs. Once a site is found they form pupae, which is similar to a cocoon and is football- or barrel-shaped. For six to twelve days they remain inside their pupae and during that time their entire body is reassembled. They grow wings and eventually emerge as adult bluebottles.
The newly adult bluebottles are strong flyers right out of the pupation and disperse quickly in order to find potential mates and new food sources. Little is known about the behaviour of adult blowflies, such as how they find mates, but once a female blowfly has mated she will travel to a food source to lay her eggs, beginning the cycle over again.
Adult bluebottles live for only around six weeks. During that time they mate repeatedly, always finding a new food source in which to lay eggs. This reduces the competition between their own larvae and ensures that even if one clutch of eggs or larvae does not survive, others will. A female bluebottle might lay up to two thousand eggs in her lifetime.