Hornets are a very large type of wasp that are similar in appearance to yellow jackets. They have four wings and six legs, along with a rounded abdomen and a thin waist between the thorax and abdomen. The area of their heads that is directly behind the eyes is wider on hornets than other wasps. Hornets are passive creatures who tend to avoid conflict. However, they may become aggressive if they feel threatened, which is usually when someone or something gets too close to their nest. Hornets have a very painful sting, and unlike bees, they can sting more than once. Someone with an allergy to wasp stings will probably be allergic to hornet stings as well, and should exercise extra caution around hornets. Whether allergic or not, multiple stings can be extremely dangerous if not treated.