Brett A. Melbourne, Penny J. Gullan & You Ning Su (1997)

Interpreting data from pitfall-trap surveys: crickets and slugs in exotic and native grasslands of the Australian Capital Territory

Memoirs of the Museum of Victoria 56: 361-367.


We use data from a pitfall-trap survey of 23 grassland sites to examine the effect of grassland type on the abundance of crickets and slugs and to demonstrate the problems associated with interpreting data obtained by pitfall-trapping. The data presented here are for four species of native cricket (Insecta: Orthoptera: Gryllidae: Bobilla victoriae Otte and Alexander, Teleogryllus commodus (Walker), Buangina anemba Otte and Alexander, Pteronemobius arima Otte and Alexander) and five species of introduced slug (Gastropoda: Pulmonata: Limacidae: Deroceras reticulatum (Müller), Lehmannia (Lehmannia) nyctelia (Bourguignat), Limax maximus Linnaeus; Milacidae: Milax gagates (Draparnaud); Arionidae: Arion intermedius Normand). The survey included three types of native grassland (Themeda, Stipa, Danthonia), two types of exotic grassland (Phalaris, Avena), and two seasons (summer, autumn). In addition to the survey, the effect of habitat structure on the efficiency of pitfall traps was examined in a well-replicated field experiment. The experiment was carried out in Themeda grassland, which was manipulated to create three levels of habitat structure. Habitat structure was found to affect pitfall-trap efficiency for crickets but not for slugs. We show that it is necessary to use knowledge of the effect of habitat structure on pitfall-trap efficiency for different species to allow confident interpretation of data from field surveys. Grassland type had a significant effect on the abundance of both crickets and slugs. Bobilla victoriae and T. commodus were both found to have high abundances in Phalaris, an improved pasture. Slugs appear to be highly invasive of native grasslands.