(b) Covered funnel trap with 15 cm diameter, for epigeal arthropods, at a distance of at least 10 m from the nearest pitfall trap, (c) and (d) ‘Absolute’ sampling method for calibrating relative methods. Sampling units usually are 5 × 20 sweeps, each sweep covering 180°. (a)-(d) Relative and absolute sampling methods for arthropods on the ground or in the vegetation, (a): Standard sized American sweepnet (38 cm diameter). Traps are filled to 1/3 with a conserving mixture of 2% formaldehyde in water, with soap added to decrease surface tension.įig. 2. A transparent roof set on wooden poles approximately 10 cm above the traps provides protection from rain. A wire mesh (1.5 cm opening) inserted in the end of the funnel prevents the capture of small mammals and amphibians. Two types of pitfall traps are most commonly used: cup traps (in our case with a diameter of 7 cm and a height of 7 cm), sunk directly into the soil, and funnel traps (in our case with a diameter of 15 cm and a funnel hight of 11cm), set in PVC tubing. Both types of flight traps are filled with water containing soap to decrease surface tension. The height of the pan can be adjusted to the height of the growing vegetation, to keep its rim approximately 50 cm above the vegetation. The yellow water-pans consist of a yellow bucket fixed to a wooden pole, again allowing easy emptying by simply turning the bucket around the axis of the screw. The pots are loosely placed in the framework and can easily be lifted from the support for weekly emptying of the traps. The window traps consist of a wooden framework, holding a glass window with a sealed rectangular plastic flowerpot underneath on each side. Technical drawings of the trap designs used in this study. We recommend the use of funnel traps with a 10–15 cm diameter ( Fig. 1) for efficiency of catching, and also for ease of use.įig. 1. Cup traps reach the efficiency of funnel traps only for the Linyphiidae (Araneae) and the Formicidae (Hymenoptera). However, during the evaluation of different pitfall trap designs we found funnel traps to be superior to cup traps ( Obrist and Duelli, 1996) in that funnel traps are up to three times more efficient per cm trap diameter in catching the following arthropod groups: Carabidae, Staphylinidae, Saltatoria, Diplopoda and Lycosidae (Araneae). Assuming that the number of individuals caught per cm diameter in any kind of pitfall trap would be at least roughly equivalent, species numbers of various pitfall trap investigations can be compared by a multiplication of trap diameter (cm), number of traps, and the number of weeks the traps were activated. If we assume random movements of arthropods on a surface, then the probability of an animal to make contact with the border of a circular trap is a linear function of the trap’s diameter, but a multitude of further parameters influence the efficiency of pitfall traps ( Luff, 1975 Adis, 1979), which complicates the comparison of data presented by different authors ( Topping and Sunderland, 1992). They have been widely used to arrive at an indication of habitat quality ( Mossakowski and Paje, 1985) and for measuring nature conservation values ( Margules and Usher, 1981 Eyre and Rushton, 1989). Pitfall traps are the best known and most often used inventory method in agroecosystems (see Figs. 1 and 2(b)).
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