The biology of Portia fimbriata, a web‐building jumping spider (Araneae, Salticidae) from Queensland: utilization of webs and predatory versatility

Abstract

The biology of a primitive salticid spider, Portia fimbriata (Doleschall), is described from observations in a Queensland rain‐forest and the laboratory. Locomotory specializations enable the spiders to move about readily on webs; and all stages of life history are associated with webs, both alien and two types they build themselves. The more flimsy Type 1 webs are used as resting sites similar to the nests employed by more familiar jumping spiders. Type 2 webs are more substantial structures in which the spider moults, mates, oviposits, broods its eggs and remains for as long as 48 days. The predatory strategy of Portia includes the use of distinct alternative tactics in the pursuit of varied types of prey. Most of these tactics are ones not usually associated with salticids. Portia invaded diverse types of webs without difficulty, including adhesive and non‐adhesive, cribellate and ecribellate, and two‐and three‐dimensional ones. Once in the web, Portia produced vibratory stimuli by specialized but varied movements of the legs and palps. Web spiders responded to these in a manner more appropriate for a potential prey item or a conspecific in its web than a potential predator. Sometimes vibrations lured the spider to the waiting Portia. Other times, localized movements were elicited which assisted Portia in remaining orientated toward the spider as it stalked across the web. Outside webs, Portia stalked other species of salticids, moving in a very slow and “mechanical” fashion and arresting forward motion whenever faced by the prey. Evidently, the salticids did not recognize Portia as another salticid and a potential predator. Although Portia pursued insects, they pursued spiders more readily, persistently and successfully. Portia captured insects outside webs, on their own webs and on the webs of other species. Those on their own webs adhered temporarily to the silk. In webs of other spiders, insects were sometimes taken directly from the chelicerae of the host. Also, their own webs assisted Portia in capturing other spiders. Eggs of spiders were fed upon both on and off webs. Different attack tactics tended to be employed with different types of prey: web spiders, lunge; salticids, swoop; insects, pick‐up. Egg‐cases were opened by means of specialized movements involving the chelicerae and the eggs were raked toward the mouth with the legs. Most prey were seized after the attack, but sometimes they were stabbed with fangs and ran several centimetres before immobilized. Portia maintained its orientation, then walked to the stabbed prey and fed. Vision of the prey seemed to be of major importance for most aspects of predatory behaviour. In the rain‐forest habitat, webs of Portia, pisaurids, pholcids, and theridiids are often contiguous and facilitate the tactic of web‐invasion. It is proposed that the pervasive use of webs by Portia is a primary character conserved from ancestral salticids, and that in the evolution of the family, invasion of contiguous webs could have led to selection for a sophisticated visual system that assisted in the localization of their residents. The developed visual system could then have allowed vagrant predation en route to more distant webs, and finally emancipation from dependence on webs altogether.