They're back. If you've spent the last few days in the Scottish countryside, you're more than likely to have experienced the familiar, infuriating prickle of an attack from Scotland's most aggressive summer resident.

After a winter's respite, armies of midges arrive as the frost disappears, hatching from May onwards and making it their mission to ruin camping trips, picnics and barbecues throughout what resembles the Scottish summer.

This year a lengthy cold snap has delayed the onslaught slightly, but Dr Alison Blackwell, one of Scotland's leading experts, predicts that the mini beasts are about return with a vengeance.

In an attempt to help potential victims prepare, her company, Advanced Pest Solutions, has developed a Midge Forecast, which is available online and as an app. It uses weather forecast information and data collected from traps to predict which areas will be worst affected.


Fact file

There are nearly 40 species of biting midge in Scotland but only five are thought to regularly attack people. The Highland midge, Culicoides impunctatus, is the most bloodthirsty. It is particularly prevalent around dawn and dusk and in the Highlands and north-western Scotland, where damp conditions provide perfect breeding grounds.

An individual midge is almost invisible to the human eye, at about a millimetre long. Only the bloodthirsty female causes us torment. The male feeds on plants and nectar, while his mate requires blood to form her eggs. Midges are alerted to human prey by the carbon dioxide on our breath. A swarm can inflict about 3000 bites per hour using a distinctive feeding technique: while mosquitos pierce the skin and suck up blood through a syringe-like mouthpiece, midges cut the skin, and then lick up the pool of blood that forms.

A midge's saliva stops blood in the wound from clotting so that it can keep on drinking indefinitely. The saliva irritates the human body and causes skin to react and swell around the site of a bite. It seems not everyone is appetising to the midge. Some will receive hundreds of bites while others escape with none.  A recent study into feeding habits found that bigger and taller people are more likely to be attacked as they provide a more substantial visual target. It also found that women are more likely to react to the bites than men – and the tendency to be a target is hereditary.

It may feel that we are the chosen victims, but midges don't just prey on humans – and there is no evidence that they favour us.  Studies have found blood in midge guts from cattle, deer, sheep, cats, dogs, rabbits and mice. Bluetongue, a debilitating disease that affects sheep and cattle, is transmitted by a type of midge.

Following the adage that prevention is the best treatment, it helps to stay inside when midges are most prevalent. They avoid direct sunlight and appear in greatest volume in the low light of early morning and evening. Midges like damp, sheltered conditions, woodland and forest areas, and do not like a breeze. Unlike many other insects, they prefer dark-coloured clothing to light.

If prevention fails, there are chemical solutions available, including insect repellents that contain DEET, or the natural alternative, citronella, which is made from lemongrass extract and can be bought as a spray or infused in candles. These work by blocking the insect’s odour receptors on the antennae and mouthparts, confusing the midge and effectively camouflaging the person. Homespun repellents include bog myrtle (the main ingredient in Bog Myrtle Ale) found growing wild across the Highlands, and thyme. Midges are also repelled by smoke, the stronger the better, so keep those Churchill cigars handy and you may find mutters of disapproval replaced by desperate requests.

If all of the above measures fail, and they probably will, you could turn from defence to attack and set a trap. There are several on the market, including the Predator, which claims to mimic a large smelly cow and attracts midges by replicating breath, heat, body odour and movement - then catching the creatures on sticky paper. During trials in 2010, a single Predator trap collected 800,000 midges over a five-day period. Instead of splashing out on a commercial trap, you could always make your own, using a plastic bottle cut in half and filled with warm sugary water and yeast. Blue Peter eat your heart out.

More than just an inconvenience, midges cause economic hardship too, costing Scotland's tourist industry an estimated £286m per year - damage to some extent offset by the knowledge that they may be in the process of becoming our least popular export. Though common in Scotland for centuries, with climate change their range is increasing, and midges are now commonly found in the Lake District and North Wales, with reports of them enjoying human snacks as far south as Cornwall. Midges clearly enjoy blue blood as much as any other kind. In 1872 Queen Victoria was forced to abandon a picnic in Sutherland after complaining of being 'half-devoured' by the beasties.

It may be that our attitude of war with the midges is at fault. They play a crucial role in the Scottish ecosystem, providing food for bats, birds and even carnivorous plants like sundews and butterworts. George Hendry, author of the best-seller Midges in Scotland, took the view that the obstacle of the midge has been partially responsible for limiting the development of the Highlands, and therefore maintaining the remarkable wilderness that, outside of the tourist season, those who live here can enjoy.