Midges favour tall men and overweight women, study finds

Midges find some people unattractive, and that impunity seems to run in families. Photograph: PA

Tall men and large women are prime targets for midges, according to researchers who surveyed people at Loch Ness, in the Scottish Highlands.

Scientists at Aberdeen University and Rothamsted Research, based in Hertfordshire, questioned 325 participants and spectators at a 120km duathlon on the shores of the loch in September 2008. Each was asked if they had been bitten and, if so, how many times.

Tall men and overweight women were statistically more likely to get bitten, the research showed. Midges tend to fly well above head height so, when they descend on groups of people, they are more likely to land on tall men first.

The survey found some evidence that women with a large body mass index were also favoured by midges, perhaps because they produce more of the chemicals, such as carbon dioxide and lactic acid, that attract the insects.

It is likely that overweight men are just as much at risk of midge bites, but there were too few in the survey to stand out.

The researchers confirmed a previous intriguing finding – that some people seem to be unattractive to midges. They found 15% were rarely bitten, and the impunity ran in families, suggesting a genetic link.

“People who don’t get bitten produce natural repellents that are extremely effective,” James Logan, an entomologist at Rothamsted who worked on the survey, said.

The tests on the duathlon participants and spectators showed those who were spared midge attacks produced a specific mixture of two chemicals, geranylacetone and methylheptenone.

“The chemicals work together. If you mix them in the right ratio, you get a fantastic repellent,” Logan said.

The natural repellent is so effective that the scientists have teamed up with an Asian company to release it as a product to deter mosquitoes, midges and ticks. It is due to be released in Asia next year and could be available in Europe in two years.

Recent research shows mosquitoes can quickly become resistant to Deet, one of the most common insect repellents. “Around half to 60% of a mosquito population can become resistant to Deet and that’s the best repellent we have at the moment, so it’s very important to discover alternatives,” Logan added.

The peak midge season in Scotland is between June and September. In some parts of Scotland, a single hectare of land can host 25m biting midges.