How Grey Squirrels Became a Deadly Threat to UK’s Native Red Populations

The population of native red squirrels in the United Kingdom has experienced a catastrophic decline, dropping from an estimated 3.5 million to under 300,000. While grey squirrels, originally from North America, continue to flourish, conservationists warn that the future of their red counterparts remains precarious.

The crisis is most acute in England, where figures vary depending on the source. The Woodland Trust estimates only 39,000 red squirrels remain, whereas the Save Our Reds campaign suggests the number may be as low as 15,000. This includes vulnerable groups in designated conservation zones such as Formby on Merseyside. In May, campaigners cautioned that if current trends persist, red squirrels could vanish entirely from parts of northern England within the next 25 years.

The conflict traces back roughly 150 years. The first confirmed introduction of greys occurred when Victorian banker Thomas V. Brocklehurst released a pair into Henbury Park near Macclesfield in Cheshire. The animals had been brought back from a business trip to the United States. At the time, the long-term ecological consequences of this release were unforeseen.

Today, the UK grey squirrel population is estimated to be between 2.5 million and 2.7 million. According to Graham Paskett of the Red Squirrel Survival Trust, these invasive rodents threaten native populations through two primary mechanisms: habitat competition and disease transmission.

Jackie Foott, representing the British Red Squirrel conservation group, emphasized that the two species cannot coexist in the same area. She described the grey squirrel as an invasive pest that causes significant damage to forestry and agriculture, costing an estimated £40 million annually. Beyond resource competition, greys carry the squirrel pox virus. While the virus is asymptomatic for greys, it is fatal to reds, causing ulcers and blindness.

Current management strategies rely heavily on lethal control methods, such as shooting and trapping. Foott noted that alternative solutions like fertility control are not yet viable without risking harm to other species, and gene therapy remains at least a decade away.

However, Paskett highlighted a potential breakthrough on the horizon. His organization is collaborating with the government’s Animal and Plant Health Agency on a field trial for oral contraceptives designed specifically for greys. The delivery system, or “hopper,” is engineered so that only greys—typically weighing around 500g—can access the bait, excluding the lighter red squirrels. If successful, this method could be available within five years.

In the interim, the reintroduction of pine martens is being explored as a biological control measure. As a native predator, the pine marten poses little threat to red squirrels, who are adept at detecting and fleeing from them. Conversely, grey squirrels often fail to recognize the danger, making them easier prey.

Reflecting on the origins of the problem, Foott remarked that early introductions were often driven by aesthetic appeal rather than ecological consideration. With a petition attracting over 75,000 signatures this year, the call for urgent action to protect the native red squirrel has gained significant momentum.