The speaker insists, right in the title, that bats don't frighten her, and then spends the poem quietly undermining that claim. The opening is calm and almost polite: bats are "denizens of the night" who drop from a "black house on the chimney." She reassures herself that they won't tangle in her hair. But the dash and the question, "isn't there?", show doubt creeping in.
What she can't shake is the bat's reputation. The "flutter and swoop," the "haunted belfries," and the "tales of the undead" crowd in, and the fear turns out to come from stories as much as from the animals themselves. The last lines mention Roethke, which seems to be a reference to the poet Theodore Roethke, though the poem doesn't spell it out. Whatever he said, she isn't convinced: those faces are "not human," and that strangeness still unsettles her.
The mood is wry and a little shivery, a mix of self-persuasion and lingering unease.