You have to stand still for summoning these weak undead. Your worm has to stay with you to eat them (6 HP undead with 6 dice). That gives the opponent enough time to place all the conjurations and summon all the creatures he needs to beat you.
Even if you feed you worm with weak creatures like bobcat (4 HP with 4 dice), you would still invest a lot of mana for only on creature.
Your worm might be strong, but he can be controlled with tanglevine, force hold, force crush, enfeeble, teleport, force push, etc.
I would not rely on only one creature.