Portia fimbriata, sometimes called the fringed jumping spider, is a jumping spider (family Salticidae) found in Australia and Southeast Asia. Adult females have bodies 6.8 to 10.5 millimetres long, while those of adult males are 5.2 to 6.5 millimetres long. Both sexes have a generally dark brown carapace, reddish brown chelicerae ("fangs"), a brown underside, dark brown palps with white hairs, and dark brown abdomens with white spots on the upper side. Both sexes have fine, faint markings and soft fringes of hair, and the legs are spindly and fringed. However, specimens from New Guinea and Indonesia have orange-brown carapaces and yellowish abdomens. In all species of the genus Portia, the abdomen distends when the spider is well fed or producing eggs.
The hunting tactics of Portia are versatile and adaptable. All members of Portia have instinctive hunting tactics for their most common prey, but can improvise by trial and error against unfamiliar prey or in unfamiliar situations, and then remember the new approach. There are differences in the hunting tactics of the regional populations of P. fimbriata. Those in Australia's Northern Territory are poor at hunting jumping spiders and better against non-salticid web-building spiders and against insects. The Sri Lanka variant is fair against other jumping spiders, and good against web spiders and insects. P. fimbriata in Queensland is an outstanding predator of other jumping spiders and of web spiders, but poor against insects. The Queensland variant use a unique "cryptic stalking" technique which prevents most jumping spider prey from identifying this P. fimbriata as a predator, or even as an animal at all. Some jumping spider prey have partial defences against the cryptic stalking technique. All types of prey spiders occasionally counter-attack, but all Portia species have very good defences, starting with especially tough skin.
When meeting another of the same species, P. fimbriata does not use cryptic stalking but displays by moving quickly and smoothly. In P. fimbriata from Queensland, contests between males usually are very brief and do no damage. Contests between Portia females are usually long and violent, and the victor may evict a loser and then eat the loser's eggs – but victorious females of P. fimbriata from Queensland do not kill and eat the losing female. If a P. fimbriata male from Queensland displays to a female, she may run away or she may charge at him. If the pair reach agreement after this, they will copulate if she is mature, and if she is sub-adult he will cohabit in her nest until she finishes moulting, and then they copulate. P. fimbriata typically copulates much quicker than other jumping spiders. Unlike in other Portia species, females of P. fimbriata do not eat their mates during courting, nor during or after copulation.
Body structure and appearance Females of the jumping spider Portia fimbriata have bodies 6.8 to 10.5 millimetres long, while those of adult males are 5.2 to 6.5 millimetres long. The Queensland variety is typically smaller than the Northern Territory variety. The cephalothorax is about 4 millimetres long and 3 millimetres wide, and the abdomen about 4 millimetres long and 2.2 millimetres wide. The front of the cephalothorax is large and angular, and the face is broad, high and flat. In Australia and Taiwan, both sexes have a generally dark brown carapace, reddish brown chelicerae ("jaws"), a brown underside, and dark brown palps with white hairs. Both sexes also have fine, faint markings and soft fringes of hair. The female has two white stripes that form an M on the cephalothorax: these stripes start at the level of the pedipalps, pass between the lateral and median anterior eyes, go up to the tufts of the cephalothorax and meet just above the pair of principal eyes. The back half of the male's cephalothorax has a white strip round the bottom edge and a white groove down the back. While male spiders' palps are larger than females', the palps of P. fimbriata females have a fringe of hair that makes them look about as large as males'. The abdomens of both sexes are dark brown, with white spots on the upper side. Wanless' female from New Guinea has an orange carapace and chelicerae with sooty markings, palps mainly light yellow, legs orange-brown, and abdomen light yellow. Wanless also found a male from the Amboina area in Indonesia, showing an orange-brown carapace and chelicerae, yellow-brown to orange-brown palps, orange-brown legs and a light yellowish abdomen.
Movement
When not hunting for prey or a mate, Portia species adopt a special posture, called the "cryptic rest posture", pulling their legs in close to the body and their palps back beside the chelicerae ("jaws"), which obscures the outlines of these appendages. When walking, all Portia species have a slow, "choppy" gait that preserves their concealment: pausing often and at irregular intervals; waving their legs continuously and their palps jerkily up and down; and moving each appendage out of time with the others and continuously varying the speed and timing. Portia′s walk is unlike that of any other spider, and this gait and the spider's fringes gives the appearance of light flickering through the forest canopy and reflecting from a piece of detritus. In Queensland, P. fimbriata walks and waves more jerkily and about twice as slowly as other Portia species, including P. fimbriata in other areas.
If disturbed, most Portia species leap upwards about 100 to 150 millimetres, often from the cryptic rest pose, and often over a wide trajectory. Usually Portia then either freezes or runs about 100 millimetres and then freezes. However, P. fimbriata in Queensland rarely runs or leaps.
Senses
Although other spiders can also jump, salticids including Portia fimbriata have significantly better vision than other spiders, and their main eyes are more acute in daylight than a cat's and 10 times more acute than a dragonfly's. Jumping spiders have eight eyes, the two large ones in the center-and-front position (the anterior-median eyes, also called "principal eyes") housed in tubes in the cephalothorax and providing acute vision. The other six are secondary eyes, positioned along the sides of the carapace and acting mainly as movement detectors. In most jumping spiders, the middle pair of secondary eyes are very small and have no known function, but those of Portia species are relatively large, and function as well as its other secondary eyes. The main eyes focus accurately on an object at distances from approximately 2 centimetres to infinity, and in practice can see up to about 75 centimetres. Like all jumping spiders, P. fimbriata can take in only a small visual field at one time, as the most acute part of a main eye can see all of a circle up to 12 millimeters wide at 20 centimeters away, or up to 18 millimeters wide at 30 centimeters away.
Generally the jumping spider subfamily Spartaeinae, which includes the genus Portia, cannot discriminate objects at such long distances as the members of subfamilies Salticinae or Lyssomaninae can. However, the main eyes of Portia have vision about as acute as the best of the jumping spiders: the salticine Mogrus neglectus can distinguish prey and conspecifics up to 320 millimetres away (42 times its own body length), while P. fimbriata can distinguish these up to 280 millimetres (47 times its own body length). The main eyes of P. fimbriata can also identify features of the scenery up to 85 times its own body length, which helps the spider to find detours.
However, a Portia takes a relatively long time to see objects, possibly because getting a good image out of such tiny eyes is a complex process and needs a lot of scanning. This makes a Portia vulnerable to much larger predators such as birds, frogs and mantises, which a Portia often cannot identify because of the other predator's size.
Spiders, like other arthropods, have sensors, often modified setae (bristles), for smell, taste, touch and vibration, protruding through their cuticle ("skin"). A Portia can sense vibrations from surfaces, and use these for mating and for hunting other spiders in total darkness. It can use air- and surface "smells" to detect prey which it often meets, to identify members of the same species, to recognise familiar members, and to determine the sex of other member of the same species.
Hunting and feeding
Hunting tactics of the genus Portia
Members of the genus Portia have been called "eight-legged cats", as their hunting tactics are as versatile and adaptable as a lion's. All members of Portia have instinctive tactics for their most common prey, but can improvise by trial and error against unfamiliar prey or in unfamiliar situations, and then remember the new approach. They can also make detours to find the best attack angle against dangerous prey, even when the best detour takes a Portia out of visual contact with the prey, and sometimes the planned route leads to abseiling down a silk thread and biting the prey from behind. Such detours may take up to an hour, and a Portia usually picks the best route even if it needs to walk past an incorrect route.
While most jumping spiders prey mainly on insects and by active hunting, females of Portia also build webs to catch prey directly. These "capture webs" are funnel-shaped and widest at the top and are about 4,000 cubic centimetres in volume. A Portia often builds her own web on to one of a web-based non-salticid spider. When not joined to another spiders', a P. fimbriata female's capture web is generally suspended from rigid foundations such as boughs and rocks. Males of Portia do not build capture webs.
A Portia can pluck another spider's web with a virtually unlimited range of signals, either to lure the prey out into the open or calming the prey by monotonously repeating the same signal while the Portia walks slowly close enough to bite it. Such tactics enable Portia species to take web spiders, such as Holocnemus pluchei Jackson, R. R.; Jakob, E. M.; Willey, M. B.; Campbell, G. E. (February 1993). "Anti-predator defences of a web-building spider, Holocnemus pluchei (Araneae, Pholcidae)". Journal of Zoology. 229 (2): 347–352. doi:10.1111/j.1469-7998.1993.tb02641.x. from 10% to 200% of a Portia′s size, and Portia species hunt in all types of webs. In contrast, other cursorial spiders generally have difficulty moving on webs, and web-building spiders find it difficult to move in webs unlike those they build. When hunting in another spider's web, a Portia′s slow, choppy movements and the flaps on its legs make it resemble leaf detritus caught in the web and blown in a breeze. P. fimbriata and some other Portia species use breezes and other disturbances as "smokescreens" in which these predators can approach web spiders more quickly, and revert to a more cautious approach when the disturbance disappears. A few web spiders run far away when they sense the un-rhythmical gait of a Portia entering the web – a reaction Wilcox and Jackson call "Portia panic".
If a large insect is struggling in a web, Portia usually waits for up to a day until the insect stops struggling, even if the prey is thoroughly stuck. When an insect is stuck in a web owned by P. labiata, P. schultzi or any regional variant of P. fimbriata, and next to a web spider's web, the web spider sometimes enters the Portia′s web, and the Portia pursues and catches the web spider.
The webs of spiders on which Portia species prey sometimes contain dead insects and other arthropods which are uneaten or partly eaten. P. fimbriata (in Queensland) and some other Portia species such as P. labiata and P. schultzi sometimes scavenge these corpses if the corpses are not obviously decayed.
When using its own web to catch other species of salticids, P. fimbriata conceals its conspicuous palps, which it does not do when stalking a web-spider or occasionally a moving fly.