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Portia fimbriata (Family Salticidae)

Fringed Jumping Spider, Portia

Distribution:

Occurs across northern Australia, in habitats ranging from savanna woodland to rainforest. (WA, NT, QLD).

Features:

Most jumping spiders are vagrant insect hunters. By contrast, Portia fimbriata is a web builder and a skilled hunter of spiders. Its body and legs are adorned with fringes and tufts of brown, white and black hairs - at rest it looks like a piece of plant litter or debris. This spider walks slowly and jerkily, bursting into action only when seizing prey. It has good vision, with the large anterior eyes so typical of jumping spiders. Males are 5 to 7 mm, and females 7 to 10 mm, in body length.

Ecology/Way of Life:

Fringed Jumping Spiders are found in webs among rocks, buttress roots, bark or foliage. In dryer habitats, they are associated with rockpile outcrops and cave entrances. The web may be a small "platform" or a more complex, inverted "cone" of silk enclosing a tangle of threads, with a curved leaf at the top. Subadult males and females live together in the same web, mating after their moult into adulthood. Females silk their eggs within the hollow of the curved leaf.

Spiders and their eggs are the preferred food of this species. Web building spiders and other jumping spiders are especially targeted. Portia fimbriata readily invades the web of its victims and those of other spiders and is skilled at moving on silk. These webs belong to spiders from at least 11 families and they can be very different (orb, sheet, space and tangle webs; dry, sticky and cribellate silk - see topic on spider webs). Web spiders have poor vision compared to the Fringed Jumping Spider.

Fringed Jumping Spiders use their behavioural skills to lull their victims into a false sense of security. Other jumping spiders seem to be taken in by this spider's slow gait and its resemblance to a piece of detritus, allowing it to move fatally close. When invading webs of other spiders, Portia uses its legs and palps to vibrate the web silk in specialised patterns. This may simulate a struggling prey animal or a male spider's mating signals, causing the web's unsuspecting owner to move toward the waiting, or slowly stalking, predator. When the victim is about 5 mm away, the Fringed Jumping Spider suddenly attacks, lunging forward, fangs outstretched to grasp its prey and inject a fast acting venom.

Persistence is typical of this spider's hunting strategy. One spider performed vibratory behaviour in a web for 3 days, before the host spider finally decided to investigate and fell victim to the invader! In another instance, when its more direct web approaches to an orb web spider were unsuccessful, the Fringed Jumping Spider left the web only to re-appear in the foliage above it. From there the hunter lowered itself down on a silk line beside the web until it was close enough to grasp the spider its victim and deliver a fatal bite.

How does this species determine which method of attack or web signal to use with a particular spider? Probably, it is through a highly developed trial and error technique, backed up by cues from the victim or its web. Portia's web signalling behaviour seem to be varied constantly until the confused victim finally responds in the right way - usually with fatal results. All of this shows an ability to solve problems unmatched by other spiders.

Interaction with Humans/Threats:

No threats to, or from this species have been identified.. Other Comments:

Originally described and placed in the genus Salticus by L. Doleschall in 1859, this species was transferred to the genus Portia by F. Wanless in 1978.

Portia was the name of a rich heiress in Shakespeare's Merchant of Venice; however, the connection to the genus Portia is not clear; the species name comes from the Latin fimbriata = fringed, referring to the fringes on the body and legs.

Further Reading:

Jackson, R.R. and Blest, A.D. (1982). The biology of Portia fimbriata, a web-building jumping spider (Araneae: Salticidae) from Queensland: utilisation of webs and predatory versatility. Journal of Zoology, London 196: 255-270.

Jackson, R.R. (1996). Portia Spiders: Mistress of Deception. National Geographic 190 (5): 104-115.

Topics: Prey capture Camouflage Mimicry Spider webs Vision

Acknowledgments:

Text & map by Mike Gray; photograph by Mike Gray, courtesy of the Australian Museum.

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