Bald Faced Hornets are among the most aggressive of all Wasps. They range from about ¾ of an inch to 1 inch in length, are stock and are excellent flyers. They are black in color, with prominent white or pale yellow markings. Hornets often will attack anyone who gets too close to their nest. Their stings are extremely painful and can trigger anaphylactic reaction in sensitive humans. 

Hornets build oval shaped paper nests that commonly are suspended from tree limbs or other similar perches. On occasion, they will build nests inside buildings, especially in attics or other unoccupied areas. Their nests can be quite large.  The entrance hole is usually located at or toward the bottom of the nest. Typically, two hornets remain outside the nest home acting as, "sentries." When alarmed, they alert the other members who will attack in masse. This can result in a person receiving hundreds of painful, potentially harmful stings at one time.