Swarm

Biomancy* Cantrip

Casting Time: 1 action
Range: 90 feet
Components: V, S, M (a spider sac)
Duration: 1 round
Class: Druid, Sorcerer, Warlock

Choose a target within range; a cloud of minuscule poisonous spiders floats on gossamer strands towards it The target must succeed on a Dexterity saving throw to avoid the spiders or become poisoned until the end of its next turn.

At Higher Levels. This spell deals poison damage on a failed saving throw when you reach certain levels. When you reach 5th level, a creature takes 1d10 poison damage; at 11th level this increases to 2d10; and at 17th level this increases to 3d10.

*can be replaced with conjuration
Source: Heliana's Guide to Monster Hunting