Midges

Highland midge (Culicoides impunctatus)

One to two millimetres long, in swarms rather than singly, and it is the females that bite. It is not a mosquito and not a blackfly: it is a biting midge, a different family with different habits, and the differences are the useful part.

The season runs from about the middle of May to September, with two generations. The second is the larger, which is why late July and August are the worst of it rather than midsummer.

It is at its worst at dawn and dusk, and on a still overcast day it does not wait for either. Bright sun and dry air work against it — it is small enough to dry out quickly.

It breeds in peat, not in water

The larvae develop in wet acidic peat: blanket bog, wet moorland, the boggy ground along a burn rather than the burn itself. They do not need running water and running water does not help them.

That distinction is why this page exists as its own page and why the forecast counts the midge as its own species. Treating it as a blackfly would have put its habitat in the wrong place entirely: our blackfly model is driven by stream density, and using that for the midge would have switched it off on the open watersheds — which is exactly where the peat is, and exactly where the midges are.

A wrong proxy is not slightly less accurate. It answers with the opposite sign.

Wind — and why our number runs high

The thing that actually governs a midge day is wind. A light breeze is enough to ground them, which is why a ridge or an open beach is bearable while a sheltered glen a few hundred metres away is not.

We do not collect wind at all. Not for the midge and not for anything else — it is simply not among the data this forecast holds. We could have put temperature in its place; we did not, because that would have passed off one measurement as another.

This has a consequence worth carrying to the numbers. On the same day the midge figure will tend to sit HIGHER than the mosquito figure. That does not mean there are more midges. It means that for mosquitoes we know limits that for midges we do not, and what we do not know cannot lower a number.

Blackfly, which is a different insect

Blackfly (Simuliidae) also appear in this forecast, in Britain as everywhere else. They are the ones that breed in running water — the larvae hold on to stones in fast shallow stretches, because they need the current to breathe — and they bite by day.

In these islands they are a far smaller nuisance than the midge, and they are shown because the model covers them across its whole range rather than because they are a British headline. Their numbers come from a Russian monograph, which is the best source we have for them and is flagged as such wherever they appear.

What actually helps

Ordinary insect netting is not fine enough. A midge goes through the mesh that stops a mosquito, and that single fact accounts for most of the disappointment people have with kit they already own.

• a head net with midge-grade mesh, not a standard mosquito net;
• cover wrists and ankles: they find the gaps rather than the face;
• choose the breezy spot over the sheltered one — a ridge, a headland, the windward side of anything;
• move the meal and the pitch away from dawn and dusk, which is a bigger win than any repellent;
• away from bog is away from midges, and a few hundred metres is already a difference.