Dutch sheep farmers are worried that a sharp rise in wolf attacks may force them to install expensive electric fencing to protect their flocks.

In the first half of this year wolves killed 138 sheep in the Netherlands, but the total for 2017 was less than 20, a wolf expert told the BBC.

It is a new problem for the Dutch - March 2015 was the first time for 150 years that a wolf had been confirmed roaming in the Netherlands.

Dogs kill far more sheep every year.

Maurice La Haye, a biologist at the Dutch Mammal Society, said: "It's very difficult to protect against a lone wolf - you can place electric fences round the sheep, but it's expensive."

He told the BBC that young lone wolves looking for mates were entering the country from Germany, expanding their territory and posing a risk to farmers.

But the threat has to be seen in perspective. He pointed out that the Netherlands has about 800,000 sheep, and dogs kill as many as 13,000 every year.

Wolf attacks can be very distressing for farmers, however. It has just been confirmed that one wolf in June killed 12 sheep and savaged 14 others, which had to be put down.

So the farmer, in Lierderholthuis near Zwolle in the eastern Netherlands, lost 26 sheep because of one wolf. The DNA result confirming it was a wolf came back only this week.

Wolves usually prey on deer and wild boar, but the increasing attacks on sheep are worrying farmers elsewhere in the EU too.

Mr La Haye said at least six wolves were spotted in the Netherlands in the spring of 2018. "Farmers would like to shoot them, but that's impossible," he said, adding that wolf-hunting was not under discussion.

Six wolf cubs have been spotted with adults in Meppen, a German town near the Dutch border.

Wolves are protected by the EU's European Habitats Directive, which bans damage or destruction of endangered species. It has enabled wolf populations to recover from decimation in the past at the hands of hunters.

The opening of borders with the collapse of communism in 1989 also meant wolves could roam more freely.

France now has an estimated 430 wolves, mainly in mountainous regions. The news website France Info says the population is growing by nearly 20% annually.

Some countries have exemptions allowing limited culling in areas where wolves are a proven threat to livestock. In northern Scandinavia reindeer have been attacked by wolves.

New wolf subsidies?
Wolf hunts in Sweden have been controversial for years. This year the authorities cancelled a winter hunt because of a decline in numbers to 305, Sweden's The Local news site reported.

The Dutch government is drafting a new handbook to give rural communities guidance on wolves.

Dutch sheep farmers interviewed by the daily De Volkskrant said it was time for the government to subsidise electric fencing to keep the wolves out.

It already pays compensation for sheep savaged by wolves, though some farmers complain that it is not enough.

Earlier this year Eise Boersma, a farmer in Benneveld near the German border, lost six sheep in a wolf attack. Since then he has installed 7,000-volt electric fencing.

Another defensive measure is to train a sheepdog, but for lowland farmers with small flocks that can be uneconomical, Mr La Haye said.

"It's very difficult to track a lone adult wolf. They can go hundreds of kilometres in a few weeks," he said.