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The year on the west coast of the Highlands
The climate figures are those of Fort William, in the heart of the affected area. The scoring combines two things that almost never coincide: the weather and the presence of the insect.
Almost every guide to Scotland organises the year the way it would for any other European country: summer good, winter bad. And on the west coast of the Highlands that sum does not work, because there is a variable that appears in no temperature table.
It is called Culicoides impunctatus, the Highland midge, and it is why many people who travel to northwest Scotland in August come back saying they would not do it again. It is not a mosquito and it carries no disease. It simply appears in clouds.
01 What it actually is
It is a tiny fly, present across much of northern Europe and Asia, which in northwest Scotland and down the western coast as far as north Wales is very prevalent from late spring to late summer. It lives in damp ground: peat bogs, fens and waterlogged areas.
Only the females bite, and the drama is worth putting in perspective: most of the blood they get comes from cattle, sheep and deer, not people. The bite feels like a slight prick or goes unnoticed altogether, and what bothers you afterwards are the lumps, which last hours or days depending on the individual.
The problem is not the individual bite: it is the number. And there is a logistical detail that surprises many people. They tend not to go into houses or buildings, but they do get into tents and cars.
02 Its three weaknesses
Here is what changes a trip. The first and most useful: the midge stops being active in winds above 10 kilometres an hour. The second: low humidity, below 60 to 75%, works against it. The third: dry, sunny conditions are unfavourable to it.
Translated into concrete decisions: the windy ridge beats the valley floor, the exposed shore beats the woodland clearing, and a dry, breezy day beats a muggy, still one, even if it photographs worse.
And now the bad news, because two things do not stop it. Rain does not deter it, and neither does darkness. Waiting for the rain to pass or for night to fall achieves nothing.
03 Why May wins
If you overlay the insect's calendar with the weather's, a window appears that almost nobody uses. In Fort William, in the middle of the affected area, May records 183 hours of sunshine — the highest figure of the year — and 71 millimetres of rain, tied with June as the driest month.
The year's four blocks
The year's sunshine maximum (138 and 183 hours), its rain minimum (78 and 71 millimetres) and the insect not yet at its peak. Average highs stay at 11.1 and 14.7 degrees, so it is cool, but this is the only moment when both variables work in your favour.
The weather is still good — 71 millimetres, 157 hours of sunshine, highs of 16.5 — and the days are very long. But the midge is already established in the damp west, so the exposed coast and the ridges work far better than enclosed valleys.
The two warmest months, 18.5 and 18.3 degrees, with high humidity, little wind and the insect season at its height. Rain also picks up in August to 98 millimetres. If these are your only options, stay on the east coast or in the cities.
The insect disappears and water arrives in exchange: rain rises from 98 to 129 and then 172 millimetres, and sunshine falls from 132 to 101 and then 74 hours. Many people take that trade without hesitating, because getting wet is predictable and midge clouds are not.
04 The time of day
Within a single day there is a pattern too. The insect is most active just before dawn and at dusk, although it bites at any hour. And it does not stray far from where it hatches: it bites close to its breeding site and near the ground, although specimens have been found up to a kilometre away.
That gives a simple rule for summer: pitching camp or stopping to eat outdoors exactly as the sun goes down is the worst possible moment. Better to eat early, or to do it high up and in the wind.
05 Winter has a different problem
The obvious solution would be to come out of season, and it does work: in winter the insect does not exist. But winter has its own trap, and it is not the cold. Average highs in January are 7.1 degrees, which is not a harsh temperature.
The problem is light. In December there are 28 hours of sunshine in the whole month, and in January 33. Not 28 hours a day, obviously: 28 hours across thirty-one days. With figures like that, a walking plan comes down to two or three usable hours a day.
06 What to bring and what does not work
What genuinely protects you is a physical barrier: clothing that covers exposed skin and, if you are camping or spending summer evenings in the west, a head net. It looks ridiculous and it is the only thing that works with absolute reliability.
As for repellents, DEET-based products are the classics, and icaridin is a more recent alternative considered safer. There is also a local tradition of using oils derived from bog myrtle, containing citronellol and limonene, though their effect is mild.
One last counterintuitive note. After an exceptionally cold winter in Scotland in early 2010, it was found that the prolonged freeze did not reduce the following summer's population: it increased it, because it had thinned out its natural predators, bats and birds.
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