If you want a quick lesson on just how the color of a British squirrel's fur matters, then spend a morning trapping with Craig Shuttleworth.

After an hour checking in lush wooded grounds near Penrhyn Castle in north west Wales we find a gray squirrel, scrabbling in a small, rectangular seed-baited cage. In no time at all it is transferred to a large plastic bag and thwacked on the head three times with a large stick.

Soon after, no more than half a mile away, we find a red squirrel in the same situation. With the law on its side, the red springs out of the opened cage and scuttles off into the woods.

As head of Red Squirrels Trust Wales, Shuttleworth spends a fair amount of his time killing grays - classed an Invasive Alien Species by the IUCN -  to "save” reds, which are classed as a native species and protected under the Wildlife and Countryside Act of 1981.

The North American gray squirrel, Sciurus carolinensis, was introduced to the UK toward the end of the 19th century. Victorian landowners saw them as a robust, tame and exotic addition. They are certainly robust but no longer exotic. A handful of animals have now spread to a population of anywhere between 3 and 5 million.

The native and once common red squirrel, Sciurus vulgaris, has been in decline ever since. No more than 140,000 thousand animals remain, confined to Scotland, Northern Ireland and pockets of Wales, north-east and north-west England and the Isle of Wight. How to reverse the linked trends has divided the country for 50 years.

Stronger and smarter

The gray squirrel has quite a charge sheet against its name. Other than simply being a foreign invader, it is accused of inflicting huge damage on trees. But it is impact on the smaller species that has seen it cast as the ecological villain.

"The gray poses two main problems for the red. The gray is a stronger, smarter, more intelligent and more robust species than the red,” says Professor Julian Chantrey of the University of Liverpool, who has spent many years studying the red squirrel population near Formby on the north-west coast of England.
"They can eat things like acorns and hazelnuts… before they are ripe and before the reds can eat them. Second, they carry the squirrelpox virus which is 95 percent fatal to reds.”

The introduced species is now the one you will likely see in any British park or woodland. People in many parts of the country may have never seen a red in the flesh. Figures as high up the establishment as Prince Charles have called for grays to be sterilized.

"Unfortunately, we did not get rid of grays early enough and we now have the situation we have inherited where they are ubiquitous,” Shuttleworth tells DW. "No one had an appreciation [when grays were introduced] of what damage can be done.”

On our morning together, the red we found accidentally trapped was outnumbered by four doomed grays. While trapping a red is not ideal it does show they are present in the area. Shuttleworth says most squirrels he kills will be dead after one blow and feel no pain.

Gray-free

Only Ireland, the UK and Italy have both the European red squirrel and the North American gray squirrel. All three countries have seen the former decline – even though it is not rare globally - and the latter increase. And all three have made numerous efforts to change that.

"I've killed thousands of these,” Shuttlesworth says, as another already stiffening gray corpse goes into the back of his jeep – destined for dissection and the compost bin. "It gives me no pleasure whatsoever.

"No one is saying they [grays] are not enchanting or acrobatic, and for many people they are often the only animals they ever see. But on the balance sheet the damage they are doing is worse.”

Shuttleworth points proudly to his own work eradicating the species from the Isle of Anglesey, several miles away across the narrow Menai Strait.

In 2015, after years of a planned eradication with community approval, the island was declared gray-free. When the program there began, it had perhaps 50 red squirrels left. With their bigger rival taken out of the picture, red numbers have mushroomed.

The plan now is to connect that population with the smaller number of reds in the county of Gwynedd through a "parsed eradication” of grays.

Unhelpful language

When Shuttleworth isn't out trapping he educates potential volunteers. The Red Squirrels Trust Wales is now working with Red Squirrels United, a new program managed by the Wildlife Trusts and funded by the European Union to the tune of £3 million ($3.9 million).

It aims to recruit 5,000 volunteers to "secure the future of red squirrels in the UK.” Read between the lines, however, and it is clearly a planned nationwide cull of the gray. And that's divisive.

"Culling them is totally pointless,” says John Bryant, an expert in "humane control of pests” who has advised Animal Aid and other organisations strongly opposed to killing gray squirrels. "If it was going to work it may have been worth it but it is not going to work. We have had cull after cull after cull … it is pointless and cruel.”

Bryant says killing the animals using cranial dispatch – favored by Craig Shuttleworth – or the air-rifle method other groups use, is far from humane as it can often lead to dead mothers and abandoned kits.

He also feels the colorful and even xenophobic language used about grays – including calling them tree rats and equating their expansion to a barbarian invasion – is disingenuous and unhelpful.

"I can't understand this business about native,” he says. "Gray squirrels never invaded, they didn't come across in little boats rowing their way all over the seas to get here. They were brought here by people.”

Friends with benefits

Julian Chantrey says there is no doubt reds fare better without grays around but believes the £3 million for Red Squirrels United is a drop in the ocean. Instead, he thinks another once common but now rare native species could help – the pine marten.

"What the Irish have done is they have shown where you have a native species – the pine marten – living alongside populations of reds and gray squirrels, the pine martens take both species of squirrel, but they preferentially take the grays because they're easier to catch, they're easier, they're heavier, there's more meat,” he says, referencing a study from Ireland.

"Even if they don't take all the grays, they reduce the numbers. And If you reduce the number of grays beyond a certain level then the [squirrelpox] disease will die out.”

Red squirrels and pine martens are found in Ireland and Scotland in healthy numbers and the Vincent Wildlife Trust (VWT) is hoping to repeat that balance in Wales. Twenty martens were translocated from Scotland to the forests of mid Wales in 2015. They successfully bred last year and more were released several weeks ago.

"We have got [camera] footage of our pine martens taking gray squirrels back to their dens,” David Bavin of the VWT says, showing DW the animal's forested habitat. The organization is doing its own research on the relationship that he thinks "will show that pine marten presence alters squirrel behavior and their density.”

"But it might not be as clear cut as ‘pine martens show up, gray squirrels disappear,'” he adds. Given the relative rarity of pine martens, in England especially, and the issues bound up with the reintroduction of a predator to agricultural habitats, it may well be some time before anecdotal evidence about pine martens and gray squirrels becomes established science.

Immuno-contraception techniques that sterilize grays (which Prince Charles approves of) may get there first. But in the meantime, the volunteers and groups who have been battling their spread for several decades show no intention of letting gray squirrels roam free just yet.