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 Portias 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.
Read more about this topic: Portia Labiata
Famous quotes containing the word senses:
“Let me obtain forgiveness of thee, Samson,
Afford me place to shew what recompence
Towards thee I intend for what I have misdone,
Misguided; only what remains past cure
Bear not too sensibly, nor still insist
To afflict thy self in vain: though sight be lost,
Life yet hath many solaces, enjoy’d
Where other senses want not their delights
At home in leisure and domestic ease,”
—John Milton (1608–1674)
“Whether or not his newspaper and a set of senses reduced to five are the main sources of the so-called “real life” of the so- called average man, one thing is fortunately certain: namely, that the average man himself is but a piece of fiction, a tissue of statistics.”
—Vladimir Nabokov (1899–1977)
“You know, Frank, I’m beginning to get a new perspective on this crawling little animal known as man. Why a dog or a cat or a bird is cleverer than any human. They sense me immediately. But these shrewd detectives of yours—. Take away one of man’s senses and you render him helpless.”
—Lester Cole (1904–1985)