Pitfall trapping for surveying trapdoor spiders: the importance of timing, conditions and effort

Abstract

Abstract. Trapdoor spiders are challenging to sample using active searching methods because of their cryptic burrowing behavior. This poses problems for ecological studies and for gathering the data needed for conservation assessments. Pitfall trapping provides an alternative method that targets adult males as they wander from their burrows in search of females. Using pitfall trapping requires considerations of the timing of sampling within the year, the effects of environmental conditions on spider activity, and sampling effort required for a high probability of detecting species that are present at a sample site. To investigate these factors, pitfall-trapping surveys were conducted at several localities in Gauteng Province, South Africa. The results showed that trapdoor spider activity occurs in all seasons. Each species has a discrete period of activity ranging from a few weeks to several months in duration. Some species are active at different times of the year at different localities. Statistical analysis showed soil moisture as the only significant predictor of activity from amongst seven environmental variables, and the survey results indicate that trapdoor spiders are active under wet conditions following rainfall. Between two and seven nights of trapping are required for a high probability of detecting all species present and active at a site, using the trap design employed for this study with ten trap arrays per site. Trapping must be repeated at regular intervals throughout the year in order to obtain a near complete inventory of the species assemblage. The number of species collected ranged from two to eight per site, with most sites having six or eight species. Pitfall trapping yielded 1.2 3.0 times the number of species obtained by active searching at sites where both methods were employed. Guidelines for planning pitfall-trapping surveys of trapdoor spiders are presented and future research directions are discussed.

South African National Survey of Arachnida (SANSA): review of current knowledge, constraints and future needs for documenting spider diversity (Arachnida: Araneae)

“…The PAs mainly include reserves and botanical gardens. The only published data is from the Roodeplaatdam Nature Reserve (Dippenaar-Schoeman et al, 1989;Engelbrecht, 2013). A species list of the spiders of the Suikerbosrand Nature Reserve is in preparation, while surveys in the following nature reserves are still underway: Kliprivierberg (Faiola et al, 2014), Serene Valley (Kelly et al, 2014), Ezemvelo , Tswaing Crater (Dippenaar-Schoeman, 2014b) and Groenkloof (DippenaarSchoeman & Lyle, 2014), as well as the Pretoria National Botanical Gardens (Kassimatis, 2008).…”

“…In the case of trapdoor spiders, a group of conservation importance, Engelbrecht (2013) identified the factors that affected species richness and activity patterns of these mygalomorphs. He showed that different species are active during different periods of the year, and that each species' activity patterns also differed between sites.…”

Niche modelling identifies low rainfall, but not soil type, as an important habitat requirement of the fossorial Australasian trapdoor spider genus Cantuaria (Hogg, 1902)

“…The burrows of I. joida become more clustered in disturbed habitats (Gupta et al 2015). A South African study used pitfall trapping to determine that males of different idiopid species are active at different times of the year and that they are most active under conditions of high rainfall and soil moisture (Engelbrecht 2013). A different study found that the rate at which birds, lizards and rodents interacted with model clay mygalomorphs increased significantly during the winter, suggesting that large spiders are more at risk of predation in winter (Mason et al 2018).…”

Beetling: A Method for Capturing Trapdoor Spiders (Idiopidae) Using Tethered Beetles

“…Commonly used methods of collecting idiopids include digging (Irish 2001;Marples & Marples 1972), and pitfall-trapping for males (Engelbrecht 2013) and nematode-infected females (Poinar & Early 1990). While often successful, these methods have obvious drawbacks.…”

“…Pitfall trapping male Idiopidae can be successful when they are searching for females at specific times during the year. For example, male Cantuaria Hogg, 1902 often leave their burrows in autumn and winter to look for females (Irish 2001), whereas female idiopids typically never leave their burrows (Engelbrecht 2013). Thus pitfall trapping is highly seasonal and is only suitable for the collection of male Idiopidae.…”