What is the length to which a worm can grow?

It depends upon the species in question as to the length to which a worm can grow.

Specifically, all animals and plants have maximum and minimum sizes to which they may mature. The particular configuration is dependent upon the animal or plant in question. In terms of worms, the longest specimen on record turns out to be ribbon worm (Lineus Longissimus) whose length in death and after time spent in sea water is documented at 179.79 feet (54.8 meters).