Abstract
Despite the severe decline that arthropod communities are experiencing worldwide, there are still basic scientific knowledge deficits that are preventing policymakers from implementing optimal decisions for their conservation. Chorological maps, fundamental conservation tools, are not available for most species or are not updated periodically in an agile way. Limited funding or an unaffordable workforce are some of the impediments to surveying species distribution. To address these challenges in the near term, several solutions have been proposed. One option involves engaging citizens in the collection of data, a method not commonly employed for studying spiders. Here, the distribution of the only spider species protected by EU legislation, the elusive Iberian endemism Macrothele calpeiana Walckenaer, 1805 (Macrothelidae) is updated by using traditional sources, but mostly citizen records, both in its native range and for the whole European continent, given that the species has frequently been unintentionally exported to various countries. The native range has been slightly expanded and currently occupies 156 UTM 10 × 10 grid cells, which means ca. 2.7% of the total area of the Iberian Peninsula. Citizen collaboration proved decisive, especially to generate recent information in a short period of time: over just the last 10 years, data from third parties covered 35 grid cells, 17 of them new to science. On the other hand, M. calpeiana has been reported as non-native in eight different countries. In some of them, such as France and Italy, the reports are recurrent. The outcomes of the methodology used in the study were highly encouraging, showcasing its potential for implementation by budget-constrained administrations to effectively monitor this species of conservation concern.