It would be a grave error to assume that the only change these spiders have undergone is their change in size.
...Somewhere in the wilderness, what looks like a giant spider egg looks ready to hatch. In fact, this egg was formed by an entire colony of spiders working together. As well as spawning new spiders, it also serves as the colony's collective mind.
Stardust has endowed the spiders with the ability to receive instructions from the colony's collective mind wherever they are, and act as one.