They have 10HP
They cause 1-2 damage on touch and poison you for 10 seconds. Poison does 1 damage on each tick, for 3 damage total.
Worms only move along walls until hit, at which point they are stunned and fall assuming they have not been killed.
While stunned, they do not deal contact damage. The easiest and safest way to deal with these is to wait for them to crawl next to you and attack them until they die.
Killing three worms causes the Boss Worm to become hostile.