Estimating the density of ground-dwelling arthropods with pitfall traps using a nested-cross array

1. A new procedure for estimating the population densities of ground-dwelling arthropods with pitfall trapping is described. It couples the fitting of single hyperbolic functions to trap data with the use of a 'nested-cross array', a cross-shaped trap arrangement with distances between traps doubling with increasing distance from the central trap. 2. We used individual-based simulation modelling to test the method's reliability given changes in population density, turning rate, trapping period, beetle distribution and intertrap distance. 3. Simulations show that function fits are more likely, and density estimates more accurate, with greater body size and therefore with net displacement, increasing population density, decreasing aggregation and increased turning rate. 4. Simulation indicates that the method is a promising procedure for density estimation that is worth testing in the field. Reliable density estimates are possible if the traps contain a neutral preservative, arrays are established in nearly homogeneous parts of habitat and the arms of the nested-cross array are distant from habitat edges.