Why does the narrator call Marner a spider again and again?

Silas Marner labours over his loom. He does not have a passion for his art, rather than he simply works at it. The spider metaphor shows Silas working away without joy. He waves like a spider because weaving is what he must do to survive.

"seemed to weave, like the spider, from pure impulse, without reflection" ; he sits at his loom with "his eyes bent close down on the slow growth of sameness in the brownish web" ; Eppie calls him away from "the repetition of his web."