In 1990, the activity of Groundbeetle communities was studied for 6 months in 4 experimental oak forests (Quercus spec) in the 'Sierra de Gata' mountains (Province of Salamanca) and another additional plot close to Salamanca city (Monovela). Using pitfall traps, a total of 3620 beetles belonging to 42 species were collected, which were divided out in 2 groups, 'frequent species' and 'less frequent species'. The relationships between these species and the characteristics of the area were established by using selected indexes. A faunistic and phenological analysis and the colonization of the different plots, emphasizing that some species of the genus Calathus Bonelli 1810 showed a clear preference for oak forests were also achieved.