Easiest worm, I am almost sure you can kill it with just leather armor but I do not recommend it if the large worm is near by.
Stronger then small but still not strong, I recommend at least diamond for this worm.
The Boss Worm is the strongest worm in the mod but the hardest to get to. I recommend at least ruby or ultimate armor for the boss worm. The boss worm drops the worm tooth for big bertha. The other ones do not unfortunetly.