Capture efficiency and preservation attributes of different fluids in pitfall traps

Pitfall traps are widely used to capture arthropods. The type of fluid employed in the traps can affect size and condition of the catch. Direct comparisons of different fluids allow entomologists to avoid suboptimal solutions, and facilitate comparisons between studies using different fluids. We compared capture efficiency and preservation attributes between five fluids in a field experiment with special respect to spiders (Araneae) and ground beetles (Coleoptera, Carabidae). Catches in pure water, ethanol-water and ethanol-glycerin were less well preserved than in brine or ethylene glycol-water. Brine and ethanol-glycerin showed low capture efficiencies, presumably because their high specific density made arthropods float and thereby facilitated escape. Only the mixture of ethylene glycol and water combined good preservation attributes with high capture efficiency, and therefore represented the best solution.