The above is a phrase from Blake's "The Sick Rose." According to a source I recently read, in Blake's time "worm" meant "dragon," or other critter, not just food for robins and moles. Might Blake have been using "worm" metaphorically?

Not sure. I just looked up "worm" in the OED, and in the 1700s one definition was "devil." What is the context?

The Sick Rose
BY WILLIAM BLAKE
O Rose thou art sick.
The invisible worm,
That flies in the night
In the howling storm:

Has found out thy bed
Of crimson joy:
And his dark secret love
Does thy life destroy.

In OE wurm or wyrm meant "serpent, dragon". According to The Online Etymology Dictionary

quote:

The ancient category of these was much more extensive than the modern, scientific, one and included serpents, scorpions, maggots, and the supposed causes of certain diseases.

So this piece is an allegory? It never quite made sense to me before.