The average bald-faced hornet’s size – excluding appendages – is 1/2 to 3/4 inch (workers are typically smaller than the queen, but similar in appearance). Compared to other yellow jacket wasps, they are extremely large. They are easier to recognize due to their unique black and white color pattern, which covers their head, thorax, abdomen, and antennae (conspicuous). Only the wings are translucent dark brown/smoky, which are folded lengthwise at rest. White or ivory markings cover their faces; they are mostly hairless. Bald-faced hornets are commonly confused with solitary bees, honey bees, yellow jackets, and hornets.
The bald-faced hornets’ nest has only one queen and plenty of female workers – 400 on average, but it can easily reach 700. A suitable nesting site is located in early spring, once the queen emerges from her hibernation place, which is either a tree stump, a log, or under loose bark. She then proceeds to lay eggs and prey on insects or collect nectar to feed the developing larvae, which will emerge as winged adults that will take over nest responsibilities and provide food and water for the colony. Just like their relatives, paper wasps and yellow jackets, July to September is the time when next season’s males and queens are born, which will get outside to mate in the fall and search for protected places to overwinter.
Their paper nests are built of wood fiber collected by queens in the spring, which comes, in most part, from vegetable fibers, dead plants, or the rotten or weathered wood of houses and surrounding wood structures. Nests are almost always built above the ground, usually in bushes and shrubbery that measure at least three feet or in tall trees (upwards of 60 feet long). Colonies may also be established under the eaves of manmade structures and protected locations. They are egg- or pear-shaped and can reach up to 14 inches in diameter and over 20 in length.
The fiber is then chewed and mixed with saliva, resulting in the paste that shapes the football-sized nest. Nests are interwoven with twigs and branches that make them more resilient in severe weather conditions and ensure their durability throughout the season. The bald-faced hornets build their inner nest with several layers of paper cells that resemble the honeybee’s comb; there are three or four tiers of combs with an opening on the bottom to allow workers’ access. There are air vents located at the top of the nest, meant to filter the air and reduce the amount of water that might infiltrate. The nest is protected by a mottled gray paper envelope.
During spring and early summer, bald-faced hornets take their protein in the form of live insects, such as spiders, flies, frogs, mantids, and sometimes other wasps. As the season progresses and insects become scarce, workers start collecting pollen from flowers, sap from trees, and also turn to scavenging for sweets, meat, and carbohydrates.
Bald-faced hornets are not necessarily more aggressive than yellow jackets and paper wasps, but they are known for their defensive behavior. When people accidentally stumble upon their nests in trees and shrubs, hornets may perceive their presence as a threat and proceed to inject venom into their skin multiple times, causing immediate pain, swelling, redness, and inflammation. For hypersensitive individuals, the sting site may spread, and the initial symptoms may be accompanied by itching and burning.
Bald-faced hornet nests should not be eliminated unless they pose a risk due to the close proximity to humans. Especially colonies built high in trees or in low-traffic areas should be left alone; warning signs informing people of their presence should reduce violent interactions.
However, if the nests are located in high-traffic areas or in the vicinity of individuals with severe allergic reactions, then professional control is required. Effective control means treating the nest directly, whose location should be identified during daytime but treatment applied only at night, when most of the hornets are inside the nest and there is less activity that would involve coming in and out. A light source is needed to illuminate the nest, but in such a manner that it points towards the nest and away from the person applying the treatment. To guard against the stings, no treatment should be applied without wearing protective equipment comprised of proper clothing, eye protection, boots, gloves, and hat. Also, avoid standing in the obvious flight route and try not to cast a shadow while applying the treatment.
For a quick kill, aerosol sprays specifically formulated for wasps and hornets or professional wasp freeze solutions are generally recommended. Some shoot a long stream of insecticide, which enables the pest control professional to attack the nest from a distance and get a quick “knockdown” effect, while other products contain foaming agents that expand when sprayed in the nest and prevent wasps from getting out. Insecticidal dusts can also be considered for nest removal, but it will take at least several hours for it to kill the entire colony (it’s also more dangerous to use, since it requires close contact to the nest).
The insecticide should be first applied near the entrance, to kill any hornets guarding the nest and ensure thorough coverage. After application, the nest should be left alone for a few days, for the poison to have enough time to kill all the workers and emerging wasps. After making sure the nest has been killed, it should be placed in a sealed garbage can and properly disposed of by a pest control company.
Bald-faced hornets are beneficial insects and their colonies should only be killed if they pose immediate risks to allergic individuals. Otherwise, it is better to leave them alone as they have an important role in controlling pest insects through predation or even encourage their presence in low-traffic areas. Biological control of individual wasps and hornets is sometimes ensured by skunks, bears, birds, reptiles, raccoons, and spiders, but there are no such known solutions to home situations.
To discourage wasps and hornets from nesting on your property, prevention should always be your first option: