Population monitoring of the endangered New Zealand spider, Latrodectus katipo, with artificial cover objects

The endangered New Zealand widow spider, Latrodectus katipo, is believed to have undergone marked population decline over the last 30 years, but as monitoring methods are time- and labour-intensive, and require observers to have a high level of experience, the current status of many populations is unknown. We investigated the use of artificial cover objects (ACOs) as an alternative monitoring tool for L. katipo at three sites at Himatangi Beach, Manawatu, New Zealand, from late 2004 through to mid-2005. Occupancy rates of the ACOs were compared with population densities obtained from habitat searches, to assess their efficacy as a monitoring tool. Numbers of the introduced spider, Steatoda capensis, which may be a competitor of L. katipo, were also recorded during habitat searches. ACOs were reliable monitoring tools, with occupancy rates higher at the site with the highest L. katipo population density. Latrodectus katipo populations were found to have highly female biased sex-ratios, with a longer breeding season at Himatangi than reported previously at other sites. Steatoda capensis exists at much higher population densities than L. katipo at Himatangi. However, fluctuations in the populations of the two species appear to be unrelated. ACOs could be used as a non-destructive monitoring tool for many other arachnid species.