A hornet is a large, aggressive type of wasp that builds paper nests and can deliver painful stings. Hornets are bigger than typical wasps, sometimes growing as long as your thumb, with bold yellow and black or white and black markings that warn other animals to stay away.

Unlike honeybees, which die after stinging once, hornets can sting multiple times, and they're much more willing to attack if they feel their nest is threatened. A disturbed hornet nest is extremely dangerous: the insects will swarm out to defend their home, and their stings hurt more than bee stings because hornets inject more venom.

Hornets build their nests from a papery material they create by chewing wood fibers and mixing them with saliva. These nests often hang from tree branches or under roof eaves, growing throughout the summer until they can be the size of a basketball and house hundreds of hornets.

The phrase stirring up a hornet's nest means causing sudden, angry trouble. If you criticize a popular teacher harshly, you might stir up a hornet's nest of angry responses. The expression captures how quickly and aggressively hornets respond to threats: what seems like a small action can trigger an overwhelming, painful reaction.