Vespula pensylvanica

Taxonomy

Order: Hymenoptera
Family: Vespidae Laicharting, 1781
Subfamily: Vespinae Laicharting, 1781
Genus: Vespula Thomson, 1869
Species: pensylvanica Saussure, 1857
Common names: western yellowjacket

Background

Like all yellowjackets, Vespula pensylvanica forages for protein and nectar but will also scavenge for dead animals and carbohydrates used by humans. Its willingness to approach food at picnic tables and roadside rest areas makes this species a pest to humans (Akre et al. 1975)(Akre et al. 1975):
Akre RD, WB Hill, JF MacDonald, amp; WB Garnett. 1975. Foraging distances of Vespula pensylvanica workers (Hymenoptera: Vespidae). Journal of the Kansas Entomological Society 48 (1): 12ndash;16..

Vespula pensylvanica is considered part of the Vl. vulgaris species group, along with Vl. flavopilosa, Vl. germanica, Vl. maculifrons, and Vl. vulgaris. This group is characterized by having an occipital carina well developed throughout its length and extending to the basebase:
the foundation of a structure
of the mandibles, and the first gastral tergumtergum:
the segments on the top side of the abdomen, often abbreviated when referring to a speciifc segment, such as T1, T2, etc.
not narrowed anteriorly or depressed. Hairs are usually pale gray or yellow. Additionally, members of this group typically have larger colonies, larger nests, and longer colony duration when compared to the Vl. rufa species group (Akre et al. 1981)(Akre et al. 1981):
Akre RD, A Greene, JF MacDonald, PJ Landholt amp; HG. Davis. 1981. Yellowjackets of North America, North of Mexico. U.S. Department of Agriculture, Washington, D.C. Handbook #552..

Distribution

Vespula pensylvanica occurs in the Canadian and Transition Zones in western North America, Mexico, and the islands of Kauai, Oahu, Maui, and Hawaii (Akre et al. 1981)(Akre et al. 1981):
Akre RD, A Greene, JF MacDonald, PJ Landholt amp; HG. Davis. 1981. Yellowjackets of North America, North of Mexico. U.S. Department of Agriculture, Washington, D.C. Handbook #552..

Diagnostic characteristics

Vespula pensylvanica resembles melanic Vl. germanica but can be distinguished by the presence of continuous yellow rings dorsally around each eye. Males of Vl. pensylvanica often lack this eye ring and can be identified by a spotted mark on the fronsfrons:
the area between the antennae and ocelli
below the antennaantenna:
a slender moveable sensory organ located on the head above the clypeus
, a slender aedeagus, and a denser apicalapical:
near or at the apex or end of any structure
region of tergumtergum:
the segments on the top side of the abdomen, often abbreviated when referring to a speciifc segment, such as T1, T2, etc.
7 (Akre et al. 1981)(Akre et al. 1981):
Akre RD, A Greene, JF MacDonald, PJ Landholt amp; HG. Davis. 1981. Yellowjackets of North America, North of Mexico. U.S. Department of Agriculture, Washington, D.C. Handbook #552..

To identify the genus:

• vertex vertex:
  the area between the ocelli and the back of the head
  not or only slightly extending above compound eyes
• distance between laterallateral:
  the side
  ocellus and occipital carina about the same as distance between laterallateral:
  the side
  ocelli
• oculo-malar space narrow, compound eyes touching or nearly touching basebase:
  the foundation of a structure
  of mandibles
• pronotum pronotum:
  a collar-like segment on the thorax and directly behind the head; extends down the sides of the throax toward the first pair of legs
  without transverse anterodorsalanterodorsal:
  top of a body part closest to the head
  carina (Kimsey and Carpenter 2012)(Kimsey and Carpenter 2012):
  Kimsey LS amp; JM Carpenter. 2012. The Vespinae of North America. Journal of Hymenoptera Research 28: 37ndash;65. Doi.org/10.3897/jhr.28.3514.

To identify the species:

• pale markings yellow instead of white
• scutum scutum:
  the largest segment on top of the thorax located between the wings and behind the head
  without stripes (as opposed to two yellow stripes as in Vl. squamosa and Vl. sulphurea)
• usually with a continuous yellow ring dorsally around each compound eye
• medial black mark on tergumtergum:
  the segments on the top side of the abdomen, often abbreviated when referring to a speciifc segment, such as T1, T2, etc.
  1 usually diamond-shaped (Kimsey and Carpenter 2012)(Kimsey and Carpenter 2012):
  Kimsey LS amp; JM Carpenter. 2012. The Vespinae of North America. Journal of Hymenoptera Research 28: 37ndash;65. Doi.org/10.3897/jhr.28.3514.
• forewing forewing:
  the front wing attached to the middle thoracic segment
  length:
  • workers: 8.5–10.5 mm
  • females: 12.5–14.5 mm
  • males: 12.5–14.0 mm (Buck et al. 2008)(Buck et al. 2008):
    Buck M, SA Marshall, amp; DKB Cheung. 2008. Identification Atlas of the Vespidae (Hymenoptera, Aculeata) of the northeastern Nearctic region. Canadian Journal of Arthropod Identification 5: 1ndash;492.

Biology/Life cycle

Nests are almost always subterranean and have a spherical or ovoid shape. Workers of Vl. pensylvanica are picnic pests due to their scavenging habits and can be a nuisance in parks, yards, playgrounds, canneries, and construction sites (Akre and Davis 1978)(Akre and Davis 1978):
Akre RD amp; HG Davis. 1978. Biology and pest status of venomous wasps. Annual Review of Entomology 23 (1): 215ndash;238..

Colonies of Vl. pensylvanica are usually annual and initiated from late April to early May. Workers and queens begin emerging in early June and September, respectively. New queens will overwinter in harsher weather and emerge in the spring with warmer temperatures. Colonies can be perennial in Hawaii and parts of southern California (Gambino and Loope 1992)(Gambino and Loope 1992):
Gambino P amp; LL Loope. 1992. Yellowjacket ( Vespula pensylvanica ): biology and abatement in the National Parks of Hawaii. Honolulu (HI): Cooperative National Park Resources Studies Unit, University of Hawaii at Manoa, Department of Botany. PCSU Technical Report, 86..

May be confused with

Vespula alascensis

• Vl. alascensis genagena:
  the cheek or side of the head
  with yellow bandband:
  usually referring to bands of hair or bands of color that traverse across an abdominal segment
  broadly interrupted by black spot in side view (Kimsey and Carpenter 2012)(Kimsey and Carpenter 2012):
  Kimsey LS amp; JM Carpenter. 2012. The Vespinae of North America. Journal of Hymenoptera Research 28: 37ndash;65. Doi.org/10.3897/jhr.28.3514.

Vespula germanica

• Vl. pensylvanica has a yellow ring around each eye
• if lacking, males can be identified by a spotted mark on the fronsfrons:
  the area between the antennae and ocelli
  below the antennaantenna:
  a slender moveable sensory organ located on the head above the clypeus
  , a slender aedeagus, and a denser apicalapical:
  near or at the apex or end of any structure
  region of tergumtergum:
  the segments on the top side of the abdomen, often abbreviated when referring to a speciifc segment, such as T1, T2, etc.
  7 (Buck et al. 2008)(Buck et al. 2008):
  Buck M, SA Marshall, amp; DKB Cheung. 2008. Identification Atlas of the Vespidae (Hymenoptera, Aculeata) of the northeastern Nearctic region. Canadian Journal of Arthropod Identification 5: 1ndash;492.

Vespula atropilosa

• Vl. atropilosa occipital carina incomplete (Higuera 2011)(Higuera 2011):
  Higuera M. 2011. Species Details: Vespula atropilosa . University of Alberta Museums. Entomological Museum. https://search.museums.ualberta.ca/g/2-38259. Retrieved December 27, 2020.

Vespula acadica

• Vl. acadica queens and workers occipital carina absent ventrally
• Vl. acadica males dorsaldorsal:
  the top surface of a structure
  surface of tergumtergum:
  the segments on the top side of the abdomen, often abbreviated when referring to a speciifc segment, such as T1, T2, etc.
  7 straight in profile, not depressed apically (Buck et al. 2008)(Buck et al. 2008):
  Buck M, SA Marshall, amp; DKB Cheung. 2008. Identification Atlas of the Vespidae (Hymenoptera, Aculeata) of the northeastern Nearctic region. Canadian Journal of Arthropod Identification 5: 1ndash;492.

Known introductions

Vespula pensylvanica has been introduced in the Hawaiian Islands (Archer 2008)(Archer 2008):
Archer ME. 2008. Taxonomy, distribution and nesting biology of species of the genera Provespa Ashmead and Vespa Linnaeus (Hymenoptera, Vespidae). Entomologistrsquo;s Monthly Magazine 144: 69ndash;101..