Abstract: The 39 known ant species of Vorarlberg (Austrian province) indicate a low mynnecofaunistic state of research. The c1imatic favoured valley of the river Rhine (Rheintal) seemed to be most suitable for an investigation in points. The investigation area is situated where the river Iii flows into the Rhine and revealed 23 species, 7 of which are recorded as new to Vorarlberg. There is a remarkable difference in the species composition between the left and right riverside of the TIl. The community on the left riverside which is bounded by Rhine and Iii shows typical riparian ants like Myrmica hellenica, Manica rubida and Formica lefrancoisi. On the right riverside there are many thermophile ants e. g. Ponera coarctata, Tapinoma ambiguum or Myrmica sabuleti. The used pitfall traps (glasstubes with 16 mm diameter; exposed for one and five days respectively) are easy to install and were only slightly beaten by additional combined hand collecting / soil sifting. The use of the more attracting rum-honey mixture or bitter cordial instead of the usual formalin meets the requirement of the short time of placing.