Both Worm ingredients come from the same Craft, done by Bazur at Great Castle.

The "Fresh Worm Head" ingredient is actually a drop from Worm Larva.

I suggest farming this route:


You can kill 5 Worms in about 20 seconds on foot, they respawn every 15s (so you're in and loop), drop chance seems to be about 50%.

I "cooked" 72 Fresh Heads and got:
- 66 Prepped Heads
- 6 Prepped Skins

So the "Great Success" chance from vendors seem to be 10%