Common Name: Bald Faced Hornet
Scientific Name: Dolichovespula maculata (Linnaeus)
This atypically large black-and-white yellowjacket gets its common name of baldfaced from its largely black color but mostly white face, and that of hornet because of its large size and aerial nest. Baldfaced hornets are found throughout the United States.
Adult workers about 5/8-3/4+” (15-20+ mm) long; queens about 3/4+” (20+ mm). Color black with white pattern on most of face, as 2 angled stripes on thorax towards head, and on last 3 abdominal segments. Head with clypeus (upper lip) broadly truncate, slightly notched at apex. Hind wing without a jugal lobe (lobe on rear near body). Pronotum in lateral view almost triangular, extending to tegula (structure at base of front wing) or nearly so. Middle tibia with 2 apical spurs. Builds paper enclosed aerial nests, grey in color.
(1) Other Dolichovespula spp. (Vespidae) with pale markings on 1st 3 abdominal segments, less than 5/8″ (15 mm) long. (2) Yellowjackets (Vespula spp.) With yellow markings including on 1st 3 abdominal segments, usually less that 5/8″ (15 mm). (3) European hornet (Vespa crabro) with pale markings on 1st 3 abdominal segments, nest envelope brown.
Baldfaced hornets are social insects which live in aerial nests. The adults are represented by workers which are sterile females, queens, and males which come from unfertilized eggs and usually appear in the late summer. Only inseminated females overwinter and do so in sheltered places. In the spring, she uses chewed-up cellulose material to build a paper carton nest of several dozen cells covered by a paper envelope. One egg is laid in each cell as it is constructed. The queen feeds the developing larvae arthropod protein material and nectar. After about 30 days, the first 5 to 7 workers emerge and shortly thereafter take over all the work except for egg laying. The nest will eventually consist of 3-5 rounded paper combs which are open ventrally and attached one below another, and are covered with a many-layered envelope. Nest size varies up to 3, 500 cells in 5 combs but usually consists of less than 2,000 cells in 3-4 combs and contains 100-400 workers at its peak (range to 636 workers). Later in the season, larger reproductive cells are built in which queens and males will be reared; males are often reared in old worker cells. The colony is then entering the declining phase. The newly emerged queens and males leave the nest and mate. Only inseminated queens hibernate and survive the winter. The founding queen, the workers, and the males all die.
The overwintering queen selects the nest site. This can vary from shrubs or vines at ground level to 66 ft (20 m) or higher in trees. Nests may also be built on overhangs, utility poles, houses, sheds, or other structures. Nearly all nests are constructed in exposed locations. At maturity, the nests can be quite impressive with sizes of up to 14″ (35 cm) in diameter and over 24″ (60+cm) in length. Often nests located in vegetation are not discovered until the leaves fall in the autumn. Nests are not reused the next season.
Baldfaced hornets are beneficial insects by helping to control many pest insect species. However, if the nest is located close to the ground and near an occupied structure or recreational area, then control is warranted. During the day locate the nest. Control should be done at night when most of the baldfaced hornets are in the nest. Only background lighting should be used and a bee veil should be worn. Apply an appropriately labelled aerosol through the entrance hole at the bottom of the nest. For high nests a “bee pole” which allows application of the aerosol from the ground or a sizeable distance away gives added safety for the applicator. The nest should be removed, placed in a plastic garbage bag, and discarded so that no emerging pupae can cause problems.