The CSI Blowfly

At this time of the year, when there has been a few frosts and the sun is weak, the most likely insect you are likely to see on the wing are bluebottles. I found this one yesterday enjoying the sun in my conservatory. It is the urban blowfly, Calliphora vicina, a very cold tolerant species which is the most common buebottle in the UK.
  Calliphora vicina is one of the most important species in forensic entomology, especially in investigating human remains. Different fly species arrive at a body at different stages of decomposition and they will lay their eggs on it. Blowflies can smell rotting flesh from large distances and are one of the earliest finding a body. They have a very fast life cycle, and they can produce up to five generations a year, depending on the temperature.

(Figure from Amendt, Krettek & Zehner 2004)

The female lays batches of 150-200 eggs in open wounds, rotten meat, or bodies. These eggs can hatch almost immediately after being laid, but they can take up to 9 days to hatch at 5 oC. The maggost will start feeding immediately. As the duration of each of the three larval stages depend on the temperature and is known in great detail, the age of the oldest maggots together with the average arrival time of the species allows to estimate the post mortem interval and approximate time of death.

Bluebottles will enter houses and lay batches of eggs in exposed meat either cooked or raw, and their attraction to rubbish makes them very abundant in cities. Bluebottles have an important ecological role as carcass decomposers...

... but they are also pollinators of several plants with exposed nectaries, such as ivy, spurges (Euphorbia) and plants from the carrot family. Some companies have even used bluebottles for greenhouse pollination of various crops as they fly at lower temperatures than bees. They also act as dispersers of fungal spores, and some fungi, like Stinkhorns (Phallus impudicus) have specific adaptations to attract blowflies, releasing chemicals that smell like rotting meat. The flies feed on the surface on the fungus and the spores attach to the fly, which can disperse them.
 Next time you are annoyed when a bluebottle enters your house, you might want to give a thought to how useful these flies are.

More information
Amendt, J., Krettek, R., & Zehner, R. (2004). Forensic entomology. Naturwissenschaften, 91 (2), 51-65 DOI: 10.1007/s00114-003-0493-5

Donovan, S., Hall, M., Turner, B., & Moncrieff, C. (2006). Larval growth rates of the blowfly, Calliphora vicina, over a range of temperatures. Medical and Veterinary Entomology, 20 (1), 106-114 DOI: 10.1111/j.1365-2915.2006.00600.x