Harvestmen are not spiders. They're arachnids and they have eight legs, but their bodies are not clearly divided in cephalothorax and abdomen, they have only two eyes and they lack spinnerets and poison glands.
Unknown harvestman (Leiobonum sp.?)
When they feel threatened they'll try to scare the attacker away with their stink glands. If that doesn't work they don't mind leaving a (still twitching) leg or two behind:
Unknown harvestman (Leiobonum sp.?), minus one leg
Not all harvestemen have long legs by the way:
Short-legged harvestman
Dicranopalpus ramosus
Many harvestmen are difficult to identify, but this is a very recognisable species: you can usually find the Dicranopalpus ramosus splayed against walls, with its legs stretched out on both sides and its long forked pedipals pointing straight ahead:
harvestman with unusually long pedipalps (Dicranopalpus ramosus)
I'm not sure if it's an illusion or not (wouldn't surprise me if it weren't, really), but while the Dicranopalpus looks normal enough when its legs are in the air it looks positively deflated when it's in its resting position:
Dicranopalpus ramosus, frontal view