The speaker is a rat catcher addressing the rats he has killed, which hang from a string as proof of his work and as payment for a bed and meal at an inn. He calls them "my beauties" and describes them with odd, tender images, like "lady's purses" and "white silk," yet also "grim grins." That mix of affection and grimness sets the tone. He knows he depends on them: he and his dog are welcome only as long as the rats are not, so the two sides are "tied together."
The mood turns more bitter in the middle. His wide hat shields him from sun and from "scorn," suggesting people look down on his trade. He then asks how "we" can live on the "crumbs of brutes," lumping himself in with the rats. By the end he seems to admire their cleverness, imagining a "canny king" among them who feasts while the rest swarm in the dark. The poem leaves us with respect, shame, and a faint sense of kinship.