The difference is in the bait presentation. A grub can be both a bottom
crawler or a swim bait. The presentation you describe, the grub is being
used as a swimbait (curly tail or paddle tail). Perfect for when a bass is
looking up and feeding on bait fish. The tube, with its tentacles is great
at emulating a crawfish and other bottom crawling creatures. A skirted grub
works great as a bottom crawler, for when bass are looking down and feeding
on crawfish.

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Craig Baugher