Bag of Spiders

This inoffensive green back has a very subtle silver web pattern to it.  A creature may reach inside and produce a handful of spiders that they may thrown in any square within 20 ft.  That creature takes 1d4+2 piercing damage from the bites and has no inherent control over the swarms they produce.  The swarms act as any naturally occurring swarm would.  

Creatures attempting to empty out the Bag of Spiders to pour a torrent of arachnids will instead find the spiders swarming out of the bag and onto the user.  That creature then takes 1d4+2 piercing from the swarm for the next three turns or until they remove the spiders somehow.

Notes: Summoning, Damage, Utility, Combat, Container