Taxonomy: why a 'hornet' is actually a yellowjacket
The common name 'bald-faced hornet' is a misnomer embedded in North American pest vocabulary. True hornets are members of the genus Vespa — the European hornet (Vespa crabro) and the Asian giant hornet (Vespa mandarinia) are the only Vespa species with any BC presence. Dolichovespula maculata is a member of the tribe Vespini, the same tribe as yellowjackets, and shares the annual colony structure, paper-nest construction, and venom chemistry of the yellowjacket group. The 'hornet' name was applied because of the species' larger size and more aggressive defensive behaviour compared to other Dolichovespula species. In BC pest management, bald-faced hornets are managed under the same wasp removal framework as yellowjackets, with additional emphasis on the larger defensive radius and more aggressive pursuit.
Physical identification: the white face diagnostic
Bald-faced hornets are readily distinguishable from yellowjackets in the field at close or medium range. The key features: predominantly black body (not yellow) with white markings on the face (the 'bald-faced' characteristic — a white or ivory facial mask covering most of the face), white banding on the abdomen (typically 2-3 white bands near the tip), and white markings on the thorax. Size: 18-25 mm — noticeably larger than a common yellowjacket (10-15 mm) and closer to the size of a bumble bee queen. Workers are uniformly black-and-white; no yellow tones. The queen is similar but slightly larger (25-28 mm). In flight, bald-faced hornets fly with the characteristic yellowjacket tuck-legged posture, not the dangling-legs flight of paper wasps. Flight is fast and direct to the nest.
| Feature | Bald-faced hornet | Common yellowjacket |
|---|---|---|
| Size | 18–25 mm | 10–15 mm |
| Colour | Black + white | Black + bright yellow |
| Nest colour | Grey-tan smooth paper football | Grey-tan layered envelope |
| Nest location | Hanging in trees, shrubs, eaves | Underground, wall voids, enclosed structures |
| Defensive radius | 5–10 metres | 2–5 metres |
| Pursuit distance | 10–20 metres | 5–10 metres |
| Peak colony size | 300–700 workers | 500–2,000+ workers |
Nesting habits and site selection
Bald-faced hornets are exclusively aerial nesters — they do not build ground nests or use structural voids as commonly as Vespula yellowjackets. The founding queen selects an aerial nest site: a tree branch fork, a dense shrub interior, an eave overhang, a wooden porch corner, or a clothesline pole. The key criterion is a sheltered, elevated anchor point. In Metro Vancouver, ornamental cedars, arborvitae, and maples are the most common bald-faced hornet nest trees because their branching structure provides multiple suitable anchor points at accessible heights. The nest is built outward from the anchor point, growing rapidly from a golf-ball-sized starting structure in May to football size by early August.
The nest location in a dense shrub creates the most common homeowner encounter scenario: the nest is invisible from outside the shrub until it's large, and the first awareness comes when a homeowner is trimming the hedge and walks into the nest perimeter. This is the scenario that accounts for most of the multi-sting events we see from bald-faced hornet encounters. The defensive response is immediate, the workers are fast, and the pursuit continues outside the shrub perimeter — a person who triggered the nest inside a cedar hedge cannot simply back away; workers will follow through the gap in the shrub.
Colony size and seasonal growth
Bald-faced hornet colonies are smaller at peak than the largest yellowjacket colonies but their sting-per-encounter risk is higher due to individual worker aggression. Colony development follows the same annual pattern as yellowjackets: founding queen solo in spring, first workers by late May, exponential growth through June and July, peak in August, decline and colony death in September-October. A typical Metro Vancouver bald-faced hornet colony has 300-400 workers by July 15 and 500-700 workers at August peak. Some colonies in optimal food-rich environments reach 800+ workers. These numbers are smaller than a peak Vespula germanica ground nest (which can reach 3,000-5,000), but a 600-worker bald-faced hornet colony in a cedar hedge 2 metres from your front walkway represents a different kind of risk.
The pursuit response: what makes them different
The characteristic that most distinguishes bald-faced hornets from other BC wasp species is their pursuit response to perceived threats. When a nest is disturbed, workers do not just defend the immediate nest perimeter — they pursue the threat actively and over a greater distance than yellowjackets. In our service experience and in the literature, bald-faced hornets have been documented pursuing threats 15-20 metres from the nest, in some cases following into buildings through open doors. This pursuit behaviour is driven by: a more sensitive alarm pheromone release threshold (they enter defensive arousal from lesser disturbance), a faster worker response time to alarm signals, and the nest's aerial, exposed location (which selects for more aggressive defence compared to the partially protected underground nests of Vespula species). A hedge trimmer at 2 metres from a bald-faced hornet nest is closer than the defensive threshold — the encounter is almost certain.
Treatment considerations
Bald-faced hornet nest treatment is the highest-PPE, highest-approach-care job in the Metro Vancouver wasp removal portfolio. Full beekeeping suit with sealed gloves and boot covers is non-negotiable. The approach requires accounting for the defensive radius — a 5-10 metre perimeter where workers may initiate defensive behaviour before any nest contact. Treatment is dust or liquid injection at the single entry hole at the base of the nest structure. The outer shell's thickness means topical aerosol application to the nest exterior is ineffective — application must go through the entry. After treatment, activity typically drops sharply within 4-6 hours as workers are unable to exit through the dust-coated entry without picking up a lethal dose. Nest removal 48 hours after confirmed colony death is optional — old nests on tree branches present no hazard and decompose over winter.