Portia labiata is a jumping spider (family Salticidae) found in Sri Lanka, India, southern China, Burma (Myanmar), Malaysia, Singapore, Java, Sumatra and the Philippines. In this medium-sized jumping spider, the front part is orange-brown and the back part is brownish. The conspicuous main eyes provide vision more acute than a cat's during the day and 10 times more acute than a dragonfly's, and this is essential in P. labiata′s navigation, hunting and mating.
The genus Portia has been called "eight-legged cats", as their hunting tactics are as versatile and adaptable as a lion's. All members of Portia have instinctive hunting tactics for their most common prey, but often can improvise by trial and error against unfamiliar prey or in unfamiliar situations, and then remember the new approach. While most jumping spiders prey mainly on insects and by active hunting, females of Portia also build webs to catch prey directly and sometimes join their own webs on to those of web-based spiders. Both females and males prefer web spiders as prey, followed by other jumping spiders, and finally insects. In all cases females are more effective predators than males.
Populations from Los Baños and from Sagada, both in the Philippines, have slightly different hunting tactics. In laboratory tests, Los Baños P. labiata relies more on trial and error than Sagada P. labiata in finding ways to vibrate the prey's web and thus lure or distract the prey. Around Los Baños the web-building Scytodes pallida, which preys on jumping spiders, is very abundant, and spits a sticky gum on prey and potential threats. A P. labiata from Los Baños instinctively detours round the back of S. pallida while with plucking the web in a way that makes the prey believe the threat is in front of it. In areas where S. pallida is absent, the local members of P. labiata do not use this combination of deception and detouring for a stab in the back. In a test to explore P. labiata′s ability to solve a novel problem, a miniature lagoon was set up, and the spiders had to find the best way to cross it. Specimens from Sagada, in the mountains, almost always repeated the first option they tried, even when that was unsuccessful. When specimens from Los Baños, beside a lake, were unsuccessful the first time, about three quarters switched to another option.
Adults of P. labiata sometimes uses "propulsive displays", in which an individual threatens a rival of the same sex, and unreceptive females also threaten males in this way. P. labiata females are extremely aggressive to other females, trying to invade and take over each other's webs, which often results in cannibalism. A test showed that they minimise the risk of confrontations by using silk draglines as territory marks. Another test showed that females can recognise the draglines of the most powerful fighters and prefer to move near the draglines of less powerful ones. Females try to kill and eat their mates during or after copulation, while males use tactics to survive copulation, but sometimes females outwit them. Before being mature enough to mate, juvenile females mimic adult females to attract males as prey. When hunting, P. labiata mature females emit olfactory signals that reduce the risk that any other females, males or juveniles of the same species may contend for the same prey.
Body structure and appearance
As in most species of the genus, the bodies of Portia labiata females are 7 to 10 millimetres long and their carapaces are 2.8 to 3.8 millimetres long. Males' bodies are 5 to 7.5 millimetres long, with carapaces 2.4 to 3.3 millimetres long. The carapaces of females are orange-brown, slightly lighter around the eyes, where there are sooty streaks and sometimes a violet to green sheen in certain lights. There is a broad white moustache along the clypeus, and running back from each main eye is a ridge that looks like a horn. Females' chelicerae are dark orange-brown and decorated with white hairs. The abdomens of females are mottled brown and black, and bear hairs of gold, white and black, and there are tufts consisting of brown hairs tipped with white. The carapaces of males are orange-brown, slightly lighter around the eyes, and have brown-black hairs lying on the surface but with a white wedge-shape stripe from the highest point down to the back, and white bands just above the legs. Males' chelicerae are also orange-brown with brown-black markings. The abdomens of males are brown with lighter markings and with brown-black hairs lying on the surface, and a short band of white hairs. The legs of both sexes are dark brown, with light markings in the femora (the sections of the legs nearest the body). All species of the genus Portia have elastic abdomens, so that those of both sexes can become almost spherical when well fed, and females' can stretch as much when producing eggs.
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 head 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 those of the 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. labiata 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 millimetres wide at 20 centimetres away, or up to 18 millimetres wide at 30 centimetres away. Jumping spider's main eyes can see from red to ultraviolet.
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, members of Portia have vision about as acute as the best of the jumping spiders, for example: 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 a Portia 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"). Unlike insects, spiders and other chelicerates do not have antennae. 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 tactics
Tactics used by most jumping spiders and by most of genus Portia
Almost all jumping spiders are predators, mostly preying on insects, on other spiders, and on other arthropods. The most common procedure is sighting the prey, stalking, fastening a silk safety line to the surface, using the two pairs of back legs to jump on the victim, and finally biting the prey. Most jumping spiders walk throughout the day, so that they maximize their chances of a catch.
Members of the genus Portia have hunting tactics 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. If a Portia makes a mistake while hunting another spider, it may itself be killed.
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. The web is initially built in about 2 hours, and then gradually made stronger. A Portia often joins her own web on to one of a web-based non-salticid spider. When not joined to another spiders', a P. labiata female's capture web may be suspended from rigid foundations such as boughs and rocks, or from pliant bases such as stems of shrubs.
A web spider's web is an extension of the web spider's senses, informing the spider of vibrations that signal the arrival of prey and predators. If the intruder is another web spider, these vibrations vary widely depending on the new web spider's species, sex and experience. 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 their size, and they 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: sticky webs adhere to cursorial spiders and to web-builders of non-sticky webs; builders of cribellate webs have difficulty with non-cribellate webs, and vice versa. Where the web is sparse, a Portia will use "rotary probing", in which it moves a free leg around until it meets a thread. When hunting in another spider's web, a Portia′s slow, choppy movement and the flaps on its legs make it resemble leaf detritus caught in the web and blown in a breeze. P. labiata 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 does not usually take the insect, but waits for up to a day until the insect stops struggling, even if the prey is thoroughly stuck. When an insect 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.