No, their venom is not geared t harm a larger animal such as a cat, and given they rarely bite, likely your cat suffers some other injury.

Cats are generally too quick to get bitten by spiders, and there is a higher probability your cat would eat the spider.

Probably not. False widow spiders are poisonous arachnids that are deadly to small vermin and other insects, but not so much for medium sized mammals such as cats. Check a veterinarian. False widow spiders are also non-aggressive, so your cat must have been too curious. If it dies, then curiousity would've killed the cat :P

And steven, that is a stupid answer. Tell stuart to get the spider to bite himself. If it kills him, it kills the cat.

my cat started holding her paw up this morning i went to work came back a couple of hours later and her foot is now double the size i need to no if a false widow spider bite would cause this /