Abstract: Ants (Hymenoptera: Formicidae) as supplementary catches in pitfall traps – how exactly do they reflect real abundance? – In ecological investigations pitfall traps are often used to sample epigaeic arthropods. Ants are also caught, intentionally or otherwise and these ants are available for later evaluation. However, it is difficult to draw conclusions about the ant community because of the particular behaviour of the species at the traps. In this paper it was attempted to evaluate the true quantity of ants with the aid of a species-specific communication factor, which describes the catch probability for individual ant species. Beginning in 1995 pitfall traps were set up on dry grassland near Greifswald in Germany. The evaluation of the ant catches was carried out with the aid of the herewith introduced species-specific communication factor determined for the three species Formica rufa, F. fusca and Lasius niger. To investigate this, the behaviour of the ants at the pitfall traps was observed and recorded. The likelihood of better evaluation of the ant coenosis is discussed, through knowledge of the catch probability for single species.