Killer bees (Africanized honey bees) are more dangerous because of how many attack at once, not because each sting is more poisonous. A single sting is about as harmful as a normal honey bee sting, mainly causing local pain and swelling unless you are allergic. The real danger is when they defend a nest: they react faster, send many more bees, and may chase a person hundreds of yards, delivering dozens to hundreds of stings. Large numbers of stings can inject enough venom to cause vomiting, orga