ÐÓ°ÉÔ­´´

While on holiday, flies were a daily nuisance when we were sitting on the hotel balcony, yet one evening the wind picked up and the flies disappeared. It seems there is a wind speed above which flies are unhappy. What is it, and why? Where do the flies go and do these variables differ between species?

• There is indeed a maximum wind speed above which they will not fly, but it also depends on temperature, humidity, sex and age of the fly, as well as its species.

For Lucillia cuprina, the major sheep-infesting fly in southern Australia, the wind speed threshold is about 30 kilometres per hour. This is the upper limit at which they can manoeuvre safely away from objects that would damage their wings. However, some fly species depend on wind transport to carry them long distances. The annoying tiny Australian bush fly is believed to migrate to Tasmania this way each summer.

L. cuprina is also grounded if it is hotter than about 40 °C, and below about 12 °C. When conditions stop them flying, they crawl into a protected space and wait until things improve.

Many species of fly live relatively short lives, measured in days. The females lay eggs or living young, according to species, which first live as a maggot and pupate underground for up to a year or more. They emerge only when conditions are right – fine, clear, sunny days with little wind, perfect to annoy the tourists.

Jan Horton, West Launceston, Tasmania, Australia

• A cyclist friend informs me that, after extensive experiments, members of Melbourne Cycling Club have concluded that they cease to be troubled by flies when riding at or above 15 kilometres per hour in still air.

Tony Heyes, Doncaster East, Victoria, Australia

• I live in subarctic Canada, where millions of mosquitoes appear during our short summer. When it is windy they hide in vegetation close to the ground, where they won’t get blown away. Walking across an apparently empty tundra will raise thousands, anxious for a quick meal of your blood.

Michael Morse, Yellowknife, Northwest Territories, Canada

• I can confirm that the maximum speed of certain flies is about 15 kilometres per hour. While cycling below that speed up mountains in the Alps and Pyrenees, flies are a constant nuisance. Not having the fitness of Lance Armstrong and laden with luggage, I found that speed difficult to sustain while climbing. It was a choice between exhaustion and grisly insect attack – I chose the latter. When outpaced, I can only presume they land on the next cyclist struggling up the same road.

Steve Lockwood, Bromsgrove, Hereford and Worcester, UK