But now, the grey squirrel is facing arguably its biggest threat yet, with plans to harness the cutting edge of genetic science to bring their destructive reign to an end.
Researchers at the University of Edinburgh’s world-renowned Roslin Institute say it is possible to cull numbers of the mammals by editing their DNA to ensure that all future females are born infertile.
The institute, famous for creating Dolly the Sheep, the world’s first mammal cloned from an adult cell, hoped to create gene-edited male squirrels that can be released into the wild.
The mammals would be altered to contain a so-called ‘gene drive’ designed to spread throughout the population, and render all females to inherit it sterile.
Males, however, would be unaffected, so as to allow them to keep spreading the new genetic code, and ultimately hastening the grey’s demise.
The initiative is supported by some as a humane means of stopping the spread of the invasive species and protected the red squirrel, which is native to the UK, but survives only in isolated strongholds, with the vast majority found in parts of Scotland.
However, animal rights campaigners dismissed the idea as “reprehensible,” and warned it would not solve long standing ecological problems.
The project, which is part-funded by the European Squirrel Initiative, a charity that promotes research into the conservation of red squirrels, would also have implications for efforts to rid Britain of other invasive species, such as mink, muntjac deer, and ring-necked parakeets.
The team at the Roslin Institute point to the fact that the grey squirrel is a carrier of squirrel pox, which is lethal to the red squirrel. Without conservation efforts, it is predicted that reds could be lost from the UK altogether by 2030.
Professor Bruce Whitelaw, the institute’s genus personal chair of animal biotechnology, is spearheading the squirrel project.
“A potential application of gene drives is to control invasive vertebrate pests, such as cane toads and rabbits in Australia, grey squirrels in the UK, possums in New Zealand and rodents around the globe,” he explained in a journal article co-authored with Gus McFarlane, a fellow researcher.
They have asked a team of genome engineers, population modellers, ecologists, ethicists and conservation experts to design gene drives as a “potential tool” to eradicate grey squirrels.
“We are investigating strategies that could humanely control the UK grey squirrel population,” Mr McFarlane said. “One is spreading female infertility.”
Another possible drive changes the sex ratio, favouring the birth of males over females until the population becomes mostly male.
Andrew Kendalll, a spokesman for the European Squirrel Initiative, said: “ “The aim would be to create a few thousand gene-edited greys and then release them so the gene spreads, slowly wiping the species out in the UK. We want to reverse the invasion.
“It is very humane - there is no need for trapping or shooting - they just stop reproducing.”
However, Jennifer White, a spokeswoman for People for the Ethical Treatment of Animals, said: “People accept that genetically engineering humans is morally unconscionable and doing the same to squirrels using gene-drive technology is just as reprehensible.
“It won’t solve our ecological problems but will lead to misery for intelligent, sensitive beings.”