Hidden from view within a large, papery nest set high in the branches of a tree; baldfaced hornets exhibit relatively sophisticated social structures. Started by a single queen who produces all of the colony’s offspring -- including workers, and eventually males and fertile females -- these nests contain several hundred individuals by the end of the summer. The sterile workers are responsible for expanding the nest, feeding the queen and -- most importantly -- feeding the developing larvae.
Baldfaced hornets are medium-sized insects, between ½ and ¾ of an inch in length. As eusocial, colonial insects; only the queens deposit eggs. After being deposited in one of the nests brooding cells, the young undergo complete metamorphosis -- beginning life as eggs, they hatch into a larvae, and pupate, before finally emerging as winged adults. Despite their common name, baldfaced hornets are not part of the group that includes the “true” hornets; instead, scientists group them with yellow jackets in the subfamily Vespinae.
Cranking Up the Colony
Colonies are annual -- only mated females survive the winter. These mated females spend the winter hiding in shelter locations such as tree hollows, under bark or rock crevices. In the early spring, they emerge from their winter refuges and find suitable spots in which to construct nests -- usually high in the branches of a tree. These new queens deposit their first clutch of eggs and -- unlike subsequent clutches -- tend to this first group of larvae themselves. The new females are sterile workers who take over maintenance, construction and husbandry responsibilities, allowing the queen to devote her time to egg production.
As the colony grows in population, the new workers increase the size of the nest. Baldfaced hornets chew wood collected from trees, bark, siding and fence posts and mix it with their saliva to produce their construction materials. At the core of the nest, a honeycomb-like structure contains numerous cells; each of which contain a young in some stage of development. Baldfaced hornets wrap paper-like materials around the outside of their nests to provide protection to the colony inside. A single hole at the bottom of the nest allows the hornets to fly in and out.
Feeding the Family
Sterile workers feed the larvae as they develop in the brooding cells. The workers primarily feed the larvae high-protein foods, such as captured insects -- caterpillars and yellow jackets are both important food sources. When it is time for the larvae to pupate, the workers cover the cells. As the summer ends and fewer larvae require food, the workers stop collecting as many insects and switch to consuming energy-rich carbohydrates, primarily flower nectar.
Dying After the Dog Days
By the late summer or early fall, the colony has reached its highest population -- potentially including up to 400 workers. At this time, the queen shifts from producing workers to producing males and fertile females, who will become new queens after mating. While the queen and the sterile workers begin to succumb to old age, predation or cold winter temperatures, the males and fertile females leave the nest and mate. The males die shortly after mating, but the mated females begin looking for a suitable winter retreat.