Vespula pensylvanica

(de Saussure, 1857)

Western yellowjacket, Western yellow jacket

Vespula pensylvanica is a social native to western North America, ranging from Mexico through western Canada. In its native range, it forms colonies with a single that typically die off in winter, with new queens to found colonies the following spring. The has become a significant pest in the Hawaiian Islands, where mild climate conditions allow colonies to become and polygynous, reaching enormous sizes—one colony on Maui was estimated at 600,000 individuals. This reproductive plasticity, combined with broad dietary habits including scavenging and on native arthropods, has caused substantial ecological disruption in Hawaii.

Vespula pensylvanica by (c) Kalvin Chan, some rights reserved (CC BY), uploaded by Kalvin Chan. Used under a CC-BY license.

Vespula pensylvanica by (c) Bob Dodge, some rights reserved (CC BY), uploaded by Bob Dodge. Used under a CC-BY license.

Vespula Pensylvanica on Foeniculum vulgare 2 by Davefoc. Used under a CC BY-SA 3.0 license.

Pronunciation

How to pronounce Vespula pensylvanica: /ˈvɛspjuːlə ˌpɛnˌsɪlˈvænɪkə/

These audio files are automatically generated. While they are not always 100% accurate, they are a good starting point.

Identification

Vespula pensylvanica closely resembles V. germanica in the yellow and black color pattern shared among Vespula . The most reliable distinguishing feature is a continuous yellow ring (-loop) around each eye, though this is absent in most males and occasionally in females. When the eye-loop is absent, identification requires examination of a spotted mark on the below the , a slender in males, and a denser region of 7. Fore wing length ranges from 8.5–10.5 mm in , 12.5–14.5 mm in females, and 12.5–14.0 mm in males. Black antennae distinguish it from the European paper wasp (Polistes dominula), which has orange antennae.

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Habitat

In its native range, found in open forest, prairies, urban zones, gardens, parkland, meadows, and houses. Nests are typically constructed 10–15 cm below ground in abandoned rodent burrows or other dark cavities, including wall voids, attics, and hollow trees. In Hawaii, occupies diverse from lowland to subalpine zones, including native forest, agricultural areas, and developed landscapes.

Distribution

Native to western North America, occurring in all states west of the Rocky Mountains from Mexico through western Canada, including the Canadian and Transition Zones. Introduced and established in the Hawaiian Islands on Kauai, Oahu, Maui, and Hawaii Island, where it is considered .

Seasonality

In native temperate range: queens emerge from in late winter to early spring (March–June peak activity), colonies grow through summer, produce new queens and males in August–September, then decline with winter onset. In Hawaii: year-round activity with flying queens captured in every month except January; colonies occur in some years.

Diet

are opportunistic and scavengers. Prey includes small insects, caterpillars, spiders, and other arthropods; in Hawaii, documented on at least 14 taxonomic orders including barklice, planthoppers, Drosophila flies, and native Hylaeus bees. Scavenges on dead animals including roadkill and dead honey bees. Adults consume from nectar and honeydew; in late season, primarily forage for sugars. In Hawaii, known to rob colonies.

Life Cycle

Colonies are typically monogynous and in native range: single fertilized initiates nest in spring, forages until 4–7 emerge, then remains in nest laying while workers assume all other duties. Colony grows through summer; males and new queens produced August–September, mate, and males die while inseminated queens enter to overwinter. Worker lifespan averages 22 days for earliest-born, 40 days for latest-born. In Hawaii, colonies may become and polygynous through queen retention or joining by outside queens, with multiple queens and year-round production.

Behavior

exhibit expressed through mauling—one worker chewing another that remains motionless—particularly when returning foragers enter the nest. Older workers are more successful in competitive attacks. Division of labor is age-dependent but not sharply defined; workers begin foraging, construction, care, and defense within four days of . Foraging includes visual search for prey and olfactory location of carrion; workers malaxate prey by removing legs, wings, and before returning to nest. Cannot communicate food locations to nestmates, so forage individually. Queens and workers fan nest when temperature exceeds 29°C. Workers modulate thoracic temperature based on protein quality of food sources.

Ecological Role

and scavenger that contributes to control. In native range, provides beneficial pest control services. In Hawaii, populations disrupt native through on arthropods including native bees (Hylaeus ) and Drosophila flies. Acts as competitor and for potentially affecting other .

Human Relevance

Major pest in western North America and Hawaii. Defends nests aggressively, with stinging increasing as colonies grow and food becomes scarce in late season. Scavenging frequent picnics, garbage, ripe fruit, and pet food, creating nuisance and sting hazards. Stings can cause severe reactions; medical treatment includes antihistamines and epinephrine for allergic individuals. every 3–5 years in fruit orchards, creating hazards for workers and high control costs. Control methods include baited traps with synthetic attractants (acetic acid combined with isobutanol, heptyl butyrate, or butyl butyrate) and mechanical removal of nests at night.

Similar Taxa

Vespula germanicaNearly identical yellow and black coloration and similar diamond-shaped black mark on first ; distinguished by continuous yellow -loop around eyes in most V. pensylvanica (usually absent in V. germanica), though this feature is unreliable in males and some females
Vespula atropilosaOverlapping distribution in western North America; requires careful examination of morphological features for separation
Polistes dominula (European paper wasp)Frequently confused by lay observers; distinguished by orange (vs. black in V. pensylvanica), open-faced nest architecture with exposed (vs. enclosed paper envelope), and lack of scavenging