Answer: B. Figurative language.
Figurative language refers to using figures of speech in order to be more effective, persuasive or descriptive. It usually relies on using words in ways that differ from their literal accepted meanings. Therefore, this allows the author to use words in an unconventional way. In this case, the phrase does not mean that the warriors literally turned into hornets. Instead, it describes te warriors as being as violent, relentless and decisive as hornets.