In Heroes of the Storm, the Witch Doctor tosses pots of spiders on his Q slot. They seem to be fairly slow and do not appear to do much damage. I think I might be using this wrong, as I tend to throw it at enemy heroes behind the minion line. How should I be using this ability?
I use this ability for map-specific harassment and I think that's the best way.
Is the enemy team trying to fight a merc camp? Throw some spiders in there for some extra damage. They won't leave the area for fear of resetting the merc camp. So your spiders will do serious damage.
Is the enemy team trying to collect a tribute? The damage from your spiders will reset the channeling.
Are you team fighting in a corridor? Your spiders will apply major damage as the enemies funnel into the area.
I don't tend to use spiders in lane, because of all the movement that can happen and to save mana. Simply backing up and waiting for the spiders to time out is a good way to mitigate a lot of this damage. I tend to only use the spiders in lane if I need to push the minion waves back or I need to help clear a lane.
Your zombie circle / range auto attack is the best form of wave clear.
If you are going to use this ability in lane, try to target melee heroes. The melee heroes will have to move back and therefore not be able to attack minions.
That's a valid and good use, assuming the spiders actually agro to the heroes and not the minions. The spiders are not good at lane pushing like the toads are, but they do make for good harass. Since they cannot be targeted, you force enemy heroes to either flee or stand there and take the damage. If you take Leaping Spiders at level 16, the spiders become a lot more useful. You have the right idea, but make sure you use them meaningfully to harass and don't just throw them because they're off cooldown