Bees
Bees are among the deadliest flying creatures on the planet. They often fly in swarms, though not always, and their sting is quite toxic. Once they insert their stingers into a victim, they release a toxin that causes people allergic to bee stings to go into anaphylactic shock. If the person is rushed to the hospital, they might have a chance of surviving. But if they run into a swarm because they disturbed a beehive, help may not come in time.