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Where do flies go in the winter? It's a question often asked and Miranda Krestovnikoff goes is in search of the answers. Her guide is Erica McAlister, the Collections Manager of Diptera (two-winged flies) at London's Natural History Museum. The location is an icy pool and woodland near Kidderminster where the conditions look anything but favourable. When they arrive nothing is flying, but Erica's backpack suction sampler (what she calls her "ghostbuster gear") reveals a host of metallic greenish flies hiding under the leaves of a tussock sedge. These are known as "dollies" to fly experts ... easier to say than dolichopodids!

These dollies are expert dancers and can be seen on most garden ponds in summer when the males pose on the surface film and wave their wings to flirt with females and threaten other males.

Flies are excellent indicators of good habitat, claims Erica. With over 7,500 species in the UK they outnumber butterflies, moths and beetles and get into every niche, so if you want to study the health of a habitat look for its diversity of flies. Producer: Brett Westwood