Published: 25th April 2025

ARC was pleased to partner with NatureScot and Amphibian and Reptile Groups of the UK (ARG UK) in conducting a study of adder status in Scotland over the last three years. The resulting evidence raises concerns about Scottish adder populations.

The study repeated methods used in an earlier project, published by NatureScot’s predecessor in 1994. A questionnaire survey targeted towards audiences familiar with land over a long period of time (e.g. farmers, crofters, other land managers) provided information on reptile distributions, perceived population changes and changes in the landscape and environment. In tandem a selection of sites were surveyed for adders and other reptiles, where possible revisiting sites from the earlier study. Other data sources were also included to map the distribution of the species. The overall aim was to check whether there had been any changes in adder status over the last 30 years.

The study found that the reported distribution shrank significantly in Scotland between 1994 and 2024. In fact, the number of ten-kilometre squares in which adders have been reported in Scotland has declined significantly, from 567 pre-1994 to 364 from 1994 onwards – a 36% decrease. However, the overall range of adders is largely the same as 1994, with the native snakes remaining absent from the Central Valley, Outer Hebrides and Northern Isles, as well as a large proportion of the upland region between Glasgow and Inverness. The authors suggest further work to confirm whether the reported sightings accurately reflect the true distribution.

The questionnaire received slightly more survey responses suggesting that adders were becoming less common than more common, though the majority of responses suggested no change or uncertainty about this.

The authors recommend that a consistent network of sites is monitored for adders and other reptiles over time through the National Reptile Survey, to provide reliable information on occupancy and population trends. Efforts can also be targeted to confirm presence or absence of adders from distribution gaps identified in the study, particularly where it appears that the species has been lost in the past 30 years. Therefore, we encourage everyone to submit their observations of adders and other reptiles across Scotland and elsewhere in Britain to established recording platforms such as iRecord or Record Pool, or for those able to commit to multiple survey visits, to sign up to take part in the National Reptile Survey.

The Great Britain IUCN Red List assessment for reptiles and amphibians considers adders to be Near Threatened in Scotland, Wales, and Britain as a whole, and Vulnerable in England. Their declines have been attributed to several pressures, including habitat loss and fragmentation, disturbance, and a lack of conservation management.

In Scotland, adders are legally protected, and appear on the Scottish Biodiversity List as a species that Scottish Ministers consider to be of principal importance for biodiversity conservation. ARC assists with adder conservation in a number of ways, for example via our Saving Scotland’s Amphibians and Reptiles (SSAAR) project.

As well as recognising the partnership with ARG UK and NatureScot, ARC would like to thank all the questionnaire participants, field surveyors, everyone who has submitted adder records in Scotland, and the various landowners, site managers and rangers for allowing access to land.

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Reference:

Ward, R.J., Gray, F.G., Foster, J., Cooper-Bohannon, R., Julian, A.M., Whatley, C., Raynor, R., and McKinnell, J. 2025. Status of the adder in Scotland (2022-24) - re-survey and comparison with the 1994 study. NatureScot Research Report 1376. URL: https://www.nature.scot/doc/research-report-1376-status-adder-scotland-2022-24-re-survey-and-comparison-1994-study