In 1902, edible dormice were released at an English estate; by 2018 Britain had an estimated 23,000, and the government now pays £40 per hectare a year to control damage to trees, crops and nesting birds

dormouseRepresentative image from Canva

In 1902, a small population of edible dormice was released at Tring Park, a private estate in Hertfordshire, as part of a Victorian-era fascination with exotic wildlife. More than a century later, that single introduction has grown into a national problem: by 2018, the Mammal Society estimated around 23,000 edible dormice lived in the UK, mostly in the Chiltern Hills. Today, the UK government pays land managers £40 per hectare per year under a Countryside Stewardship scheme to control these invasive rodents, which strip bark from trees, damage fruit crops and predate hole-nesting birds, according to official reports from GOV.UK. Read on to know more about it here:From estate curiosity to invasive speciesThe edible dormouse (Glis glis) is native to continental Europe and parts of Asia, not the British Isles. It was first introduced to the UK in 1902 at Tring Park in Hertfordshire, where it was kept in a semi-wild state on the estate. Over the following decades, some individuals escaped or were deliberately released, establishing a free-living population in nearby woodlands.Unlike many introduced species that fade away, edible dormice thrived. They are long-lived for a rodent, can breed successfully in woodland and orchard habitats, and have few natural predators in the UK. By 2018, their range had expanded to cover much of the Chiltern Hills and adjacent woodlands, with the population centred within about 35 km of Tring Park. The Mammal Society’s estimate of roughly 23,000 individuals marks the edible dormouse as one of Britain’s most successful invasive mammals.How edible dormice damage trees, crops and birdsEdible dormice are classified by the UK government as an invasive non-native species (INNS) because of the harm they cause to native habitats and species. Their most visible impact is on trees. In early summer, they strip bark from the crowns of pole-stage or mature trees, leaving distinctive rectangular patches. This can cause stem breakage, forking and, in severe cases, tree death. Preferred species include larch, Scots pine, Norway spruce, beech, birch and orchard trees.In orchards and other fruit-growing areas, dormice feed on fruit crops, reducing yields and quality. They also predate hole-nesting birds, taking eggs and chicks from nest boxes and natural cavities in trees. This combination of bark stripping, crop damage and predation makes them a significant problem for forestry, horticulture and wildlife conservation in the regions where they are established.Why the government pays land managers to control themBecause edible dormice are invasive and cause measurable economic and ecological harm, the UK government has created a dedicated funding stream to support their control. Under the Countryside Stewardship Higher Tier (CSHT) scheme, the “CSP20: Edible dormouse control and management” action pays land managers £40 per hectare per year for 10 years to reduce dormouse populations and limit damage.The aim of the action is clear: to control the population of invasive non-native edible dormice in order to reduce their impact on tree bark, fruit crops and hole-nesting birds, thereby supporting habitat and species recovery. Payments are made only where dormice are present and where land managers have an agreed species management plan with Natural England or the Forestry Commission. Participants must carry out baseline monitoring, agreed levels of culling, and habitat impact assessments in years 1, 5 and 10 of the agreement.How control is carried out—and the rules around itControl of edible dormice is tightly regulated to ensure it is humane, targeted and does not harm protected species. Management by trapping requires a specific wildlife licence (CL02) from Natural England. Trapping is typically carried out from May to August, when dormice are active and easier to catch.Land managers are advised to:Place traps in suitable habitat and minimise the risk of capturing non-target species.Bait traps for up to five days before setting them; if bait is taken, the trap can then be set.Check traps daily and release any non-target species as soon as possible.Maintain the health and welfare of any trapped animal and dispatch caught dormice humanely, usually by cranial concussion or an approved spring trap.Carcasses must be disposed of responsibly, for example by incineration or burial, with additional permissions required on sites of special scientific interest. All activities must comply with animal welfare legislation, including the Wild Mammals (Protection) Act 1996 and the Animal Welfare Act 2006.Not to be confused with the protected hazel dormouseA key challenge in managing edible dormice is avoiding harm to the native hazel dormouse (Muscardinus avellanarius), which is a protected species. The two look similar to non-specialists, but they differ in size, tail characteristics and habitat preferences. Government guidance stresses the importance of correct identification using non-native species secretariat (NNSS) ID sheets and, where necessary, advice from Natural England or Forestry Commission officers.Mistaking a hazel dormouse for an edible dormouse could lead to illegal killing of a protected species, so land managers are urged to be cautious and seek expert support if unsure.A long-term, landscape-scale problemThe edible dormouse story is a classic example of how a small, seemingly harmless introduction can become a long-term management issue. What began as an estate curiosity in 1902 has evolved into a landscape-scale problem requiring coordinated monitoring, licensing and funding.By paying land managers to control dormice in key areas, the government aims to limit further spread, reduce damage to trees and crops, and protect vulnerable wildlife such as hole-nesting birds. At the same time, the scheme reflects a broader shift in UK policy toward proactive management of invasive non-native species, recognising that prevention is far cheaper and more effective than trying to reverse established invasions.For now, the Chilterns remain the epicentre of the UK’s edible dormouse population, but occasional reports from other parts of the country serve as a reminder that vigilance is needed. Without continued control and monitoring, the legacy of that 1902 release could extend well beyond the woodlands of Hertfordshire and Buckinghamshire.