Dolichovespula maculata is a species of wasp in the genus Dolichovespula and a member of the eusocial, cosmopolitan family Vespidae. It is taxonomically an aerial yellowjacket but is known by many colloquial names, primarily bald-faced hornet, but also including bald-faced aerial yellowjacket, bald-faced wasp, bald hornet, white-faced hornet, blackjacket, white-tailed hornet, spruce wasp, naked brink, and bull wasp. Technically a species of yellowjacket wasp, it is not one of the true hornets, which are in the genus Vespa. Colonies contain 400 to 700 workers, the largest recorded colony size in its genus, Dolichovespula.

The bald-faced hornet is distributed throughout the United States and southern Canada, but is most common in the Southeastern United States. Males in this species are haploid and females are diploid. Worker females can, therefore, lay eggs that develop into males.

Taxonomy and phylogenetics

The bald-faced hornet gets its name from the characteristic white markings on its face, as the word "bald" in English is derived from the word "piebald".

D. maculata is found in forested areas and in vegetation in urban areas. Nests are generally located in trees and bushes, but occasionally are found under rock overhangs or the sides of buildings. Vertical distribution of nests has been recorded from heights of above ground level.

Behavior

Bald-faced hornets are omnivorous, and considered to be beneficial due to their predation of flies, caterpillars, and spiders. Their aggressive defensive nature, though, makes them a threat to humans who wander too close to a nest or when a nest is constructed too close to human habitation. They vigorously defend the nest, with workers stinging repeatedly, as is common among social bees and wasps. The bald-faced hornet has a unique defense in that it can squirt or spray venom from the stinger into the eyes of vertebrate nest intruders. The venom causes immediate watering of the eyes and temporary blindness.

Colony cycle

The life cycle of a colony can be divided into the founding stage, the ergonomic stage, and the reproductive stage. Colonies show annual cycling. New nests are generally founded during spring and early summer by a single queen, though temporal specifics vary depending on location. In Washington, nest initiation occurs during mid-May, and workers emerge during mid-June. Large-cell building starts during mid-July, and the first queens emerge during mid-August. The colony terminates during mid-September, for a life cycle around 4 months (122 days).

Cuticular hydrocarbons

Cuticular hydrocarbons serve as a barrier to moisture diffusion, so prevent dehydration in wasps. Cuticular hydrocarbon profiles vary over species and nests, and they are a proposed mechanism for nest-mate recognition. Worker and queen cuticular lipids have similar components, but their distributions differ dramatically, implying that cuticular hydrocarbons also play a role in caste differentiation.

Cuticular hydrocarbon profile and dimorphism among castes

The following lipid profiles were determined from specimens collected in the summer and early fall of northeastern Georgia in 1989. The dominant hydrocarbons recovered from the cuticles of workers were n-alkanes and methyl- and dimethyl-branched alkanes with a C27 or a C29 backbone. The major lipids and their distributions in workers were: n-heptacosane (28%), 11-13-methylheptacosane (15%) 3,13-dimethylheptacosane (11%), and 13 and 15-methylnonacosane (10%). Nonacosene composed 34% of cuticular lipids in the queen. The average chain length of identified cuticular lipids is 28.0 in queens and 27.5 in workers.

Worker-queen conflict

D. maculata is characterized by low paternity, worker reproduction, and queen-worker conflict. Divergent genetic interests between workers and their queen cause intranest struggle for control, which disrupts social organization. Because of haplodiploidy, workers are unable to mate, but their unfertilized eggs become males. Workers and their queens are most related to their own sons. Natural selection then favors those workers that produce their own sons rather than rearing the queen's brood. In a sampling of seven D. maculata nests, 20.9% of males were produced by workers. The percentage of males that were workers' sons did not correlate with the time during which nests were collected or colony size. Because worker relatedness is so high in D. maculata, workers are more related to other workers' sons than to the queen's own sons, so worker policing of egg production does not occur. An explanation for the queen's near monopoly on male production is that worker production is costly, so reduces total colony reproduction. The cost toward worker production acts as a selective pressure on the workers, so they are more likely to exercise reproductive restraint.

Workers in reproductive nests may kill their queen so they can reproduce. When researchers<!-- t the University of Sheffield --> examined a collection of 19 D. maculata nests during the reproductive phase of their life cycle, they found that 14 nests did not have a queen. Matricide might occur after a sufficient workers have been raised and queen-destined eggs have been laid. However, matricide has not been directly observed and other causes of death are possible.

Diet

Diet in D. maculata varies depending on an individual's life cycle stage and geographic location. Adult yellowjackets, like true hornets, are predatory, and prey upon several insect types. They have been observed consuming meat, spiders, fruit, and insects. Adults also drink flower nectar, which they feed to their larvae.

Parasites

Female bee moths (Aphomia sociella) have been known to lay their eggs in bald-faced hornet nests. The hatched larvae then proceed to feed on the eggs, larvae, and pupae left unprotected by the wasps. This infestation can destroy large parts of the nest as the larvae tunnel throughout it looking for food.

Life cycle

Each spring, queens that matured and were fertilized at the end of the previous season begin new colonies. A queen selects a location for her nest, begins building it, lays a first batch of eggs, and feeds this first group of larvae. These become workers and assume the chore of expanding the nest. They chew up wood, which mixes with a starch in their saliva. They then spread it around with their mandibles and legs, and it dries into a papery structure. The workers guard the nest and feed on nectar, tree sap and fruit pulp (particularly that of apples). They also prey on insects and other arthropods, chewing them up and feeding them to the larvae. They have been known to scavenge raw meat. In late summer and early fall, the queen begins to lay eggs that become drones and new queens. After pupation, these fertile males and females fly off to mate. Fertilized queens then overwinter and start new colonies during the next year. Males and workers die in the end of the cycle. The old queen, if not killed by workers, dies with them around mid-autumn.

References

  • Bald-faced hornet at PestWorld.org
  • Bald-faced hornet at Hornets: Gentle Giants
  • Bald-faced hornet at Study of Northern Virginia Ecology. Fairfax County Public Schools, VA