The behaviours used by Pholcus phalangioides (Fuesslin) (Araneae, Pholcidae) to evade its predators were studied with particular attention being given to a special defence behaviour, whirling. To whirl, this long-legged web-building spider swings its body around in a circle, with its legs remaining on the silk. Experiments were carried out to determine the types of stimuli that elicited whirling. Touching the spider or its web elicited whirling, as did air movement over the spider, but there was no evidence that chemical stimuli from potential predators were important. Small juveniles differed from adult females and larger juveniles by more often dropping from the web instead of whirling when confronted by a potential predator. Besides catching prey on its own web P. phalangioides invades other spiders' webs to catch the other spiders. By whirling in alien webs, P. phalangioides could deter attacks by the resident spider, but P. phalangioides was less inclined to whirl when in an alien than when in its own web.