Some features influencing the efficiency of pitfall traps

Summary

• 1. Some of the trap features influencing the ability of pitfall traps to catch Coleoptera, especially Carabidae, were investigated by field and laboratory experiments.

• 2. It is shown theoretically that the catch of circular and rectangular traps can be compared on a basis of their perimeter lengths. Formulae are given for the reduction in catch per trap when traps are placed close together in a grid.

• 3. Field experiments compared the catch of six types of trap, from 2.5 cm diameter glass tubes, to 2 m long sections of guttering. Glass traps were most efficient in proportion to their size; plastic and metal traps had a reduced catch. Small traps were most efficient in catching small species, whereas large traps caught relatively more large beetles.

• 4. The capture efficiency of each type of trap was tested in the laboratory, using six species of Carabidae. Traps caught about 75% of beetles that contacted their perimeter; only small traps caught small beetles efficiently; the largest species was caught poorly by nearly all traps.

• 5. The rate of escape, from each type of trap, of small, medium and large sized Carabidae was tested. Escape was negligible from glass-sided traps, but was about 4% per day from plastic traps, and 10% from metal ones. Large beetles escaped most from small traps, and small beetles from large ones.

• 6. The observed differences, between types of trap, in capture and retaining efficiencies accounted for some, but not all, of the variations in catch found in the field.