The Alaskan Bull worm is a massive worm that only appeared in the SpongeBob SquarePants episode Sandy, SpongeBob, and the Worm and the video game Creature from the Krusty Krab. The worm easily destroys property by eating it. It is one of the largest creatures in the series, as its mouth is mistaken to be a giant cave, its tongue is mistaken to be a giant worm, and its size is enough to crush an entire city.
At the Krusty Krab, SpongeBob gives everybody a description of the worm; he says it is big, scary, and pink and "all wiggly", to which he wiggles to justify his point. Sandy says she can easily fight the worm because she wants to get her tail back, and SpongeBob unsuccessfully tries to stop her numerous times on her journey. SpongeBob and Sandy arrive (after seeing a "worm sign") at the mouth of the worm mistaken as a giant cave. Sandy enters the mouth and fights with the tongue, which she thought was the giant worm. SpongeBob reminds Sandy that is not the worm but just its tongue. They are later chased by the worm, until they happen to lead the worm off the edge of a cliff where it crushes the newly moved Bikini Bottom. Afterwards, it is revealed to speak, although its only vocal is a long "Ouch!".
Its acts of destruction include eating signs, buildings, SpongeBob's home, a fish's butt (twice), and crushing Bikini Bottom.
It's similar to the Graboids, from the Tremors series, which are also giant worms. The end of the episode, which showed the Alaskan Bull Worm fall off the cliff, also parodied the end of the first Tremors movie.
Sandy's "Worm sign" comment is a direct reference to the Dune book series by Frank Herbert.
Although the worm is large in general, there seems to be a slight inconsistency as to how large the worm actually is. When first seen, he is easily distinguished as being about triple or quadruple Sandy's height, however, when chasing SpongeBob and Sandy, he seems to have shrunken considerably. When Spongebob and Sandy were riding him, the worm seemed to have grown once again. Lastly, he was large enough to land on and crush the entire city. Likewise, at the beginning of the episode, he was small enough to travel through the city to eat buildings.
It makes a video game appearance in Chapter 4 of the SpongeBob Video Game: Creature of the Krusty Krab.
Exactly why the worm is bigger than most of the characters is unknown, though it may have been either that this episode takes place after "Mermaid Man and Barnacle Boy IV", or the worm was mutated by the radiation left over from Operation Crossroads in the Bikini Atoll, which may explain why the characters can talk in the first place.
It may also be a reference to the worm's apparent origin from Alaska and Sandy's mistaken belief that she (being Texan) can handle it - Alaska is the only American state larger than Texas.