When doors and windows are wide open on warm summer days, one of the unwelcome visitors they invite to venture into our homes is the Bluebottle Fly.
These chunky two-winged flies are large, fast-flying and noisy. The reason they are unwelcome is, of course, that females seek out dead flesh, like meat or fish on a kitchen worktop, to lay their eggs on.
A female Bluebottle Fly enters an open house and does a quick reconnaissance of the available rooms in her quest for a place to lay. Finding nothing, she departs again to explore the possibilities in a neighbouring house. Otherwise she may persist in trying to exit via a closed window thereby affording the householder an opportunity to swat her.
The act of laying eggs by the fly is called 'blowing' and uncovered meat with eggs on it is said to be 'fly-blown'. The Bluebottle Fly is therefore often called a 'blow fly' because of its egg-laying habit or simply a 'blue fly' because of the bright metallic blue colour on its abdomen.
Buzzing female flies seek out uncovered meat, fish, dead animals, garbage and faeces to blow on. Bluebottle Flies are social animals in that females often travel in groups. Furthermore, if a female finds a good source of food she emits an odour, a pheromone, to alert others to the food source.
Females lay about 500 eggs during their short lifespan that lasts only a few weeks; one month at the most. The eggs hatch into off-white, worm-like maggots that feed on the decomposing matter.
At this time of year, garbage in a waste bin is a common source of maggots. If the maggot survives to maturity it will crawl away from its food source and bury itself in soil where it turns into a tough brown cocoon. After a few weeks, the cocoon splits and an adult fly emerges to seek a mate and perpetuate the cycle.
Adult Bluebottle Flies feed on nectar so they are plant pollinators. Because of the females' attraction to rotting flesh, feeding adults are particularly drawn to flowers with what we regard as an unpleasant or bad smell. A flower with a bad smell may be unattractive to us but it is an evolutionary triumph in exploiting the common and widespread Bluebottle Fly to pollinate it.
The wriggling, off-white maggots have their uses too as they are sometimes used by anglers as fishing bait.