Country and Coast: No sting in the tail of the flies in disguise

Most gravitate to our conservatory where, if I leave the doors and windows open to set them free, others want to join the fun. If I close the windows to deter them, those already inside risk death from a lack of sustenance, too much heat or utter boredom. I've discovered that if I leave the tiny windows of the lantern open at night, most seem to find their way to freedom.

Inevitably, some end their lives on the floor, where the solution is a vacuum cleaner, but it is sad to see the death of such interesting and attractive insects. These are not troublesome household flies that we try to swat with the Yorkshire Post, but delightful harmless creatures.

In America they are known as flower flies but here they are wasp or bee mimics. That is a problem because many of us think they are genuine wasps, honey bees or even bumble bees. Because hoverflies lack stings, their only defensive mechanism is to mimic dangerous insects.

By late summer, the season's young birds have discovered it is unwise to try catching wasps, honey bees or bumble bees. As summer progresses, young birds haven't learned that hoverflies are defenceless – their disguise keeps them safe. Their resemblance to so many varieties suggests there are many species of hoverfly. For example, there are more than 300 in Holland; lots of ours migrate from the continent.

Hoverflies, as the name suggests, hover over most types of flower. They seek nectar and in so doing help bees and wasps to fertilise the plants. As they hover, their wings move with such speed that they (the wings) become invisible if only for a moment, then they settle on the flower.

Another of the hoverfly's benefits is that its larvae eat troublesome aphids – the larvae of syrphus ribesii, for example (that looks like a wasp) can kill up to 800 aphids during its two weeks larval period. If you look closely at those on your garden flowers you'll note several different species in a very small area but don't kill them or be afraid of them. They are your hovering friends.

www.nicholasrhea.co.uk

CW 11/9/10