I've been able to kill even alphas with a crossbow and about 75 fire arrows. When the Deathworm comes out of the ground, shoot one fire arrow, then while its going underground, run past it (I changed the setting so some player stats were a bit higher) I had about 350% movement speed. Easy solo kill.
Ragnarock - Go into ice cave and kill the weak deathworms there. Use a good shield to block their attacks and melee them with a sword, easy quick kills because they have so little health and they drop the same loot as a regular deathworm. Make sure to wear warm cloths.