8-legged freaks..
i have yet to watch this, but based on a spiders anatomy, they are quite fragile. even the largest spiders (such as the goliath birdeater, see attached pic) may weigh only a few ounces.
there are two types of tarantulas: Arboreal and Terrestial. arboreals are climbers and rarely will spend any time on the ground. they are found in trees, and spend almost all their time in their homes, waiting for prey to come to them. terrestials are ground dwellers, and will usually dig a burrow out for a home. sometimes terrestials will try to climb, but they risk death from a simple fall of even a few inches. their bodies will break apart easily, especially at the conjunction of their abdomen to their carapace. their legs can fall off as well. the legs may grow back slowly with each molt. but they have no coagulents in their blood, so any rupture in their skin will result in them bleeding to death. in captivity it may be stopped by applying a sealant, such as vaseline to the wound to stop the bleeding.
as far as giant spiders, they may be difficult to stop if you cant shoot them in what passes for 'brains'. their skin acts like an exoskeleton as they have no bones just like a crab or lobster. but a crab or lobster must have a harder shell to survive being underwater.
their poison is a paralyzing substance, administered by their fangs. the goliath birdeater will grow fangs over an inch in length.
if you were attacked by a giant spider ala 8 legged freaks, i'd say you should be able to break off their legs with your bare hands. but they would be fast and strong as well. most spiders however hate water, so a firehose may be a good way to fend off an attack from a 5 foot high spider.
http://www.wcsscience.com/biggest/spider.html