Human beings have attempted to weaponize just about everything that could plausibly be used to give us a military advantage over our adversaries. So it's no surprise that at various times in world history, armies have employed the bites and stings of our invertebrate friends to torment the opposition. Although they don't play quite the pivotal role in military history as machine guns and submarines, these nasty critters did make a difference. And believe it or not, we're still developing new entomological weapons today.
In cases of special need, the Roman legions would sometimes use beehives as makeshift "bombs," lobbing them over the walls of besieged fortresses with catapults. The ensuing chaos would make it much easier for Roman archers and artillery to hurt their defenses. Roman sailors also sometimes filled clay jars with bees and lobbed them onto the decks of enemy ships.