The speaker tells us more about the worm; it has found the rose's bed.
The status of this "bed" is ambiguous. It could be just a place where the rose sleeps that happens to be "crimson."
It could also be a "bed" of something, like a "bed of roses" (not unlikely since the poem is called "The Sick Rose") or something else that's red. This would make the rose a gardener of some kind.