Why do spiders have 8 legs and not 6 or 4 instead?

Answer 1

Excellent question! The earliest arthropods we know of had bodies made up of a series of segments, some of which had a pair of legs each. If you look at a centipede, for instance, that sort of body plan is still around. For various reasons (most of which we don't know, and some of which we can only guess at) certain groups within the arthropods settled on a certain number of body segments and number of legs. Some of those legs became very specialized sensory organs (antennae), some became "holders" (pedipalps or palps), some became claws, etc. Spiders have only 2 body parts, the abdomen and the fused cephalothorax (head and middle region merged together). The middle region (thorax) is the fused leg-bearing remains of the multiple segments of earlier arthropods, and in spiders it has only 8 legs left. In addition, spiders have 2 pedipalps up near the front of the body, which help them manipulate food (or if they're male spiders, which serve as sexual organs). Spiders don't have specialized antennae, but they have various information-gathering devices on their various legs, such as special vibration-detecting hairs and (if I remember correctly) scent detectors.
Insects only have 6 walking legs, but they have 2 specialized information-detecting legs that we call antennae.
As to why spiders have 8 walking legs, presumably it's because that number works well and there's no strong driving force to change for most spiders. There is a group of spiders that imitates ants, though, and they run around holding their first pair of legs up in the air just like ant antennae. It is possible that over time, if there is a selective advantage to using those legs as sensory organs, this greoup of spiders may have those legs become more antanna-ish and less walking-leg-ish. Of course, none of us will be around to see it.

Answer 2

In general the possession of 8 legs allows spiders to move with greater facility in directions other than forwards.spiders can often be seen moving backwards or sideways rather than forwards. TADA!!! Yah, it was the evolution over time and stuffs...

Answer 3

That is how arachnids developed, the better to navigate webs, perhaps.
Insects have 6.
Evolution worked out so that number of legs was optimal for the species.

Answer 4

Spiders are arachnids. All arachnids have 8 legs. These include spiders, scorpions, ticks and mites.

Answer 5

Why have you got 2 arm`s & two leg`s ?
why has a dog got 4 leg`s ?
why ?
why ?
why ?

Answer 6

It helps in web making

Answer 7

Because they are from mars they came in an asteroid bowie knew that years ago.

Answer 8

Because they would limp and they wouldn't be able to get away when we go to stamp on them!

Answer 9

because they are arachnids... this family of species have 4 limbs. it's in their genes.

Answer 10

Y do u bother?