The bald-faced hornet (Dolichovespula maculata) is a large, black and white wasp known for its distinctive nest and aggressive defense of its colony. Despite its common name, this insect is not a true hornet (genus Vespa), but rather a species of aerial yellowjacket native to North America. Due to its size and powerful sting, the bald-faced hornet is often perceived as a significant threat. Understanding its identification, the effects of its sting, and its specific behaviors helps assess the actual danger it poses to humans.
Identifying the Bald-Faced Hornet
The bald-faced hornet is easily distinguished from other wasps and yellowjackets by its unique black and white or ivory coloration, rather than the more common yellow and black. Workers can reach up to three-quarters of an inch in length, making them larger than most other yellowjacket species. The “bald face” refers to the prominent white markings on the front of its head, along with white patches on the thorax and the tip of the abdomen.
The most recognizable sign of a bald-faced hornet colony is its nest, a large, football-shaped structure made of paper. These nests are constructed from chewed wood fiber mixed with saliva, resulting in a grayish, papery shell. They are typically suspended high off the ground in trees and shrubs, but can also be found attached to buildings or other man-made structures. Mature nests can grow quite large, sometimes reaching over two feet in length, and may contain several hundred workers by the end of the season.
Assessing the Sting Risk
The sting of the bald-faced hornet is intensely painful, and the insect can sting repeatedly. Unlike the honey bee, the bald-faced hornet possesses a smooth stinger that does not detach, allowing it to inflict multiple stings on a perceived threat. Entomologist Justin Schmidt rated the pain of this sting at a 2.0 on his Schmidt Sting Pain Index.
For most people, a single sting results in localized symptoms such as immediate pain, burning, swelling, and itching at the injection site. The primary danger, however, comes from the potential for a systemic allergic reaction, known as anaphylaxis, in sensitive individuals. Anaphylaxis is a life-threatening medical emergency that can cause symptoms like difficulty breathing, rapid pulse, dizziness, or swelling away from the sting site. Since multiple workers can sting a single person, the amount of venom injected increases exponentially, raising the risk of a severe reaction near a disturbed nest.
Understanding Defensive Behavior
Bald-faced hornets are not generally aggressive when foraging for food, but they become fiercely territorial and defensive when their colony is threatened. Their aggression is directly tied to protecting their nest, which they will defend vigorously against any intruder. Their defensiveness is influenced by the colony’s population size, which peaks in late summer and early fall, typically August and September.
Common triggers for an attack include vibrations near the nest, accidental contact, or sudden, rapid movements in the vicinity. Workers will swarm when they perceive a threat, often attacking in a concentrated, coordinated manner. A unique defense mechanism is the ability to squirt venom from its stinger toward the eyes of an attacker. This venom spray causes immediate, intense irritation, temporary blindness, and watering of the eyes.
Safe Encounter Strategies
The safest strategy when encountering bald-faced hornets is to maintain a distance of at least 10 feet from their paper nest. If a nest is located near a home, attempting a do-it-yourself removal is strongly advised against due to the high risk of multiple stings. Attempting to spray or knock down an active nest will trigger an aggressive mass defense, often resulting in homeowners being stung repeatedly.
Instead, the presence of a nest near human activity warrants contacting a licensed pest control professional. Professionals can employ proper protective gear and nighttime removal techniques when the insects are less active. Simple preventative measures can reduce the likelihood of attracting individual hornets, such as keeping outdoor garbage cans tightly sealed and cleaning up sugary spills or fallen fruit. In the event of a sting, a person experiencing systemic symptoms like difficulty swallowing, widespread swelling, or shortness of breath must seek immediate medical attention.