Predators such as spiders are particularly vulnerable to habitat fragmentation and are considered good bio-indicators of nature conservation or habitat degradation. As occurs all around the globe, the Uruguayan coastal sand dunes have been drastically diminished and fragmented, and seriously affected by human modifications such as urbanization, tourism, and introduction of exotic species. The objectives of the present study were to identify the indicator species of two adjacent areas of the sandy coastline of Uruguay (Marindia, Canelones) and, specifically, to confirm whether Allocosa brasiliensis can be considered a biological indicator of the open dunes with scarce psammophile vegetation in this locality. We used the IndVal method which quantifies the indicator value of each species. Allocosa brasiliensis had the highest indicator value for open dunes fixed with psammophilic native vegetation, reflecting its greatest specificity and fidelity to this environment.