parakkum has noted that historic battles with swords and such never really occurred like they did in films. IIRC, they usually just had some mild skirmishing, followed by one side getting scared, retreating, and getting slaughtered as they ran away.

Bees and hornets, on the other hand, do full, thrash-'em-out, give-no-quarter, gore-fest battles. This video of hornets attacking a beehive would certainly get an R rating and use up plenty of the special effects budget. WARNING: do not watch the film if you find bees gore disturbing.