Question

When Grendel says Hrothgar's "warriors became hornets" (40), what literary device is being used?

Answer 1

The device used here is metaphor.  Hrothgar’s men do not become hornets but they fight with the ferocity of hornets whose nest was bothered. Even if Grendel is impervious to their weapons, they fight to defend what is theirs.  Later on, Grendel would feel the pain he inflicted on others when he fought Beouwulf.