Apart from experimental design, the selection of pitfall trap size, collecting fluid and habitat type sampled may also influence the capture efficiency of the method. We combined three field studies from two very different geographic areas, in which the efficiency of pitfall traps, using carabid beetles (Coleoptera: Carabidae), is evaluated. First, we showed that ethylene-glycol is a more efficient collecting fluid compared to commercial anti-freeze, paraffin and salt water in collecting beetles in a forest patch in South Africa. Second, we showed that larger traps (90 mm mouth diameter) are more efficient in collecting carabids than small traps (65 mm) in a meadow in Finland. We also showed that for these large traps, commercial vinegar was a better collecting fluid than propylene-glycol, but that for small traps, propylene-glycol was superior to vinegar in collecting carabids. Finally, we showed that the trappability of Pterostichus oblongopunctatus and Carabus hortensis differed in enclosures placed into two different habitat types (a forest and a clear-cut in Finland), while trappability did not differ significantly for two other species (Calathus micropterus and Pterostichus niger) in these habitat types. However, for the two Pterostichus species studied, the catches in traps placed in the centre of the enclosures were slightly higher in the clear-cut, compared to the forest, and catches were higher in enclosures with rich field-layer vegetation, compared to enclosures with poor vegetation. The three studies re-emphasise the uncertainties of using pitfall traps in ecological studies. However, with careful planning and standardisation to help avoid erroneous interpretations, pitfall trapping is an invaluable method for the field ecologist.
Pitfall-Trap Sampling of Ground-Dwelling Invertebrate Predators in Japanese Orchards: Effects of Pitfall Trap Size