Opening and closing of burrows by an arid-adapted Ariadna sp. (Araneae: Segestriidae) during a heavy rainy year

The Ariadna spiders (Araneae: Segestriidae) inhabiting the gravel plains of the Central Namib Desert construct individual burrows with a circular entrance surrounded by a ring of small pebbles; sometimes they closed their burrows by a small stone. At the lichen fields about 20 km east of Walvis Bay (Namibia), there is a consistent population of Ariadna spiders that can also use lichen bits in the ring composition and as plug when the burrow is closed. As part of our long-term research on this population, we sampled and monitored 175 burrows between December 1999 and August 2000. In March 2000 an exceptionally high rainfall occurred in the Namib, leading to flooding even on our fieldwork station. So we wanted to test whether and to what extent an event of this magnitude could affect the burrow closing. Our results point out that the rainfall influences the closing behaviour of Ariadna sp. and suggest that the flooding event can result in a potential and unexpected resource pulse for these spiders.