THEY have been described as "the ultimate blood-sucking machines".

Scotland’s dreaded biting midges have long plagued campers, ramblers and hillwalkers across the nation’s countryside, often leaving victims with hundreds, sometimes thousands, of bites.

And now scientists have discovered that the pesky beasties are actually carrying scores of diseases we never knew about.

For the first time, researchers have looked at the total collection of viruses midges carry and discovered some interesting results.

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The team, from the Medical Research Council and University of Glasgow Centre for Virus Research (CVR), discovered several new viruses in the "virome" of the midges, including an alphanodavirus, two rhabdo-like viruses and a chuvirus.

Some of the viruses can prove deadly to animals such as pigs and herons, but the scientists say there is no evidence that they pose a threat to humans.

Sejal Modha, lead author of the study, published in the journal Viruses, said: "The technology we used allowed us to look at the viruses carried by midges in a way that can’t be done in the lab, expanding our knowledge of the insect viruses in a way that could be very useful in future.

"What we found is important because biting midges can be carriers of arboviruses; and although midges are not currently a public health concern in Scotland - and we stress there is nothing for the public to be concerned about - our research gives us a better understanding of midges and the viruses they may carry, helping us prepare for any possible future emerging risks through improved surveillance and knowledge."

The midge Culicoides impunctatus breeds in vast numbers across large swathes of Scotland, and feasts on blood.

Usually emerging at dawn or dusk, they come out in force, leaving their human victims itching for days.

However, despite their prevalence in Scotland, midges are currently understudied.

Carriers of arboviruses, viral infections transmitted to humans from a group of insects, midges were responsible for the emergence and spread of Schmallenberg virus (SBV), which affected cattle, sheep and goats in Europe in 2011, and are likely to be involved in the emergence of other arboviruses in Europe.

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There are at least 41 different species of biting midge described in the UK, of which 37 are present in Scotland.

The midges studied were collected at the University of Glasgow’s Scottish Centre for Ecology and the Natural Environment (SCENE), located within the Loch Lomond and Trossachs National Park.

Joseph Hughes, co-author of the study, claimed there are likely to be many more undiscovered insect viruses across the world.

He said: “What we found is the tip of the iceberg in terms of discovering new viruses.

“With an estimated 5.5 million insect species on Earth, there are likely to be several million more insect viruses to be discovered.

"What we are seeing globally, due to several factors including climate change, is the movement of virus vectors -- or carriers -- to new regions.

"Our research is important because the emergence of SBV in Europe, which is transmitted by biting midges, and the incursion of multiple strains of bluetongue virus into Europe, means we need to understand more about the diversity of viruses carried by biting midges.

"By increasing our understanding, we can hopefully be better prepared for viruses that may emerge in the midge population in future."

In recent years, Scots have been warned of growing numbers of midges, with last year described as the “worst year ever”.

They arrive late in the season sue to severe snow storms, but experts said rising temperatures later in the year had brought out the highest levels ever recorded.

Midges typically begin to emerge during the end of May, and in June the female biting midges arrive to kick off the season.

In 2017, experts estimated another bumper year for the insects with a record number of 68 million descended on the country.

Lucy Fraser, who runs a guest house on the West Highland Way, has to warn visitors not to open the windows during peak midge season.

She said: “I insist the guests don’t open the windows. If they do it’s horrific and believe me some do and regret it.

“Each year from the end of May to October I become a prisoner and wouldn’t dare go out the door before 10am and after 5pm. This is when the midge is at its worst, the sun keeps them away, but the rain attracts them. I’ve been here 22 years and it gets worse every year.”

Meanwhile, the insects are also being spotted much later in the year, with reports suggesting they can still be seen in December some years.

In recent years, warm Autumn weather has resulted in third hatchings of biting midges.

Dr Alison Blackwell, the world’s leading experts on midges, previously said it was “very unusual” to see them as late as December but called on the public to get in touch with her if they do see the insects later in the year.

She said it can be caused by “unseasonably warm weather” in Autumn months, which probably feels like spring to the midges.

“Instead of dying out in September or October as usual, a few stragglers of the later hatch keep going into winter,” she said.

Midges have been around since prehistoric times, with dozens of species now spread around the world.

Most don't bite but the Scottish biting midge is a blood-seeking predator.

Lured to Scotland by mammals at the end of the last ice age, the species has been estimated to be responsible for 90% of all bites on humans in Scotland.

Scientists have described how the insects pierce human skin, using their head to gyrate "like a jigsaw power tool".

The tiny insects can then gorge on double their bodyweight in blood before flying off.

Flying midges are estimated to cost Scotland around £286million annually in tourism, as many tourists who have encountered them vow not to return.