As long as your not in "Peaceful" mode they appear at night with the other mobs (monsters) and in caves and mine shafts.
you have to kill spiders
Spiders spawn at night and in dark areas.
Yes.
You can't.
you get carrots in minecraft from baby zombies on chickens or spiders, you have to kill them and then you will get them.
Currently, no.
Increases damage to spiders, cave spiders, silverfish and endermites.
It does extra damage to spiders and cave spiders, nothing else.
bane of arthropods does extra damage to spiders, cave spiders, and silverfish
Kills spiders faster
When they hit you, you get poisoned for 10 seconds.
In the dark. Also in a wide open area.