Hornets are wasps which are closely related to yellowjackets. There are approximately 20 hornet species ranging from tropical Asia (which most live) to Europe, Africa, and North America. The North American Hornet is actually the European hornet which was introduced by humans.
The hornet is a social insect which their hive(s) consist of a paper like construction made from the pulp they make by chewing wood and they live the entire time from egg to adult inside the community hive.
The majority of hornets in a hive are female. They perform duties in the hive such as construction of the hive, feeding the young, protection of the colony and gathering food. The queens are the dominate species in the hive and the only ones to reproduce. The males sole job is to reproduce with the queen and soon die after their job is done.
Hornets abandon their hives in colder climates in the winter and the new young queens along with their eggs protect themselves by finding protection in human structures or under tree bark.
During the spring the queen will start a new hive by her young taking over the tasks of the new hive which in turn leaves the queen for reproduction. Prior to the queen dying she will produce a generation of new males, which are called drones, and new queens.
Hornets dine on flies, bees and other insects along with the occasional snack on tree sap.
Usually hornets will not sting humans unless they are provoked. In Germany the hornets are granted protection by the government to ensure their role in the ecosystem is protected.