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 close their burrows by a small stone. In the lichen fields, about 20 km east of Walvis Bay (Namibia), there is a consistent population of Ariadna spiders that can also use pieces of lichen both in the ring composition and as the plug when the burrow is closed. We sampled and monitored 175 burrows repeatedly between December 1999 and August 2000. In March 2000, an exceptionally high rainfall occurred in the Namib, leading to flooding even in our fieldwork station. We tested whether and to what extent an event of this magnitude could affect burrow closing. We found the rain event increased burrow closure by large, but not small or medium-sized, Ariadna sp. We suggest that the flooding event acted as an ecological resource pulse for these spiders. Keywords: flooding, lichen-stone fields, Namib Desert, spider population, survival strategies.