Effectiveness of pitfall trapping

We aimed to evaluate the effect of the trap diameter size, the fixing solution and their combination on the capture efficacy for harvestmen (Opiliones) and millipedes (Diplopoda). We expected to find a higher species diversity and abundance of both groups in larger traps. We also expected that larger species would be captured less in smaller traps than in larger traps. We used pitfall traps with three different diameter sizes; 3 cm, 5 cm and 12 cm, filled with three types of fixing agents (saturated solution of NaCl, 10:1 mixture of 70% ethanol and glycerol and 4% formaldehyde). Altogether 90 traps representing nine combinations of the trap diameter and fixing solution were placed in the field in the spring and autumn term. The dataset represents the list of recorded species and their epigaeic activities (pooled for spring and autumn period) captured in pitfall traps differing in solution type and diameter size. The mean body sizes of millipedes and harvestmen weighted by the species abundances were calculated for each trap.