Western yellowjacket

📖Overview

Vespula pensylvanica is a social wasp native to western North America, commonly found around human activity where it scavenges sweet foods and protein. Colonies are annual in much of their native range but can become perennial and invasive in places like Hawaii. Workers are aggressive defenders of nests and are often seen at picnics, garbage bins and orchards.

Colonies are founded in spring by a single queen (in temperate areas) and grow through summer into large nests containing hundreds to a few thousand workers. In tropical or disturbed environments, nests can persist year-round and produce multiple queens, which has contributed to its invasive success on some islands.

🔍How to identify a western yellowjacket

Adults are compact, robust wasps with a characteristic bold pattern of yellow and black on the head and abdomen. The face and pronotum have yellow markings; the abdomen shows alternating black and yellow transverse bands and usually a terminal black band. Legs and antennae are dark. Queens are larger and more robust than workers; males (drones) have slightly different abdominal markings and longer antennae.

1. Robust wasp 10-16 mm with bold alternating black and yellow bands on the abdomen
2. Face and thorax marked with yellow and black, with a complete yellow ring around each eye; stout, compact body compared with long-bodied paper wasps
3. Nests usually underground in rodent burrows, sometimes in wall voids or other cavities; enclosed papery nest rarely exposed
4. Behavior: flies rapidly and gleans food from surfaces; frequently seen at human food and trash

Lookalikes

↻Life cycle

1. 🥚

   Egg

   Laid by the queen in individual brood cells; eggs hatch in a few days depending on temperature.

2. 🐛

   Larva (grub)

   Larvae are fed chewed insect prey and protein by workers; this stage lasts several days to a few weeks while they grow.

3. 🫛

   Pupa

   Larvae spin a cocoon in the cell and pupate, transforming into adults over several days.

4. 🐝

   Adult

   Workers forage for carbohydrate and protein; new queens and males are produced late season. In temperate climates new queens overwinter and start new colonies in spring.

🍃Diet and predators

🌱Effect on plants and gardens

Adults feed on nectar and honeydew and therefore can act as incidental pollinators, but their main ecological role is as predators and scavengers feeding on other insects and animal protein; they rarely damage plants directly.

How to get rid of western yellowjackets

Reduce attractants: cover garbage, compost and outdoor food; pick up fallen fruit; keep sugary drinks covered. Seal entry points into buildings and block wall or roof voids. Trap or baiting programs can reduce local numbers—use commercial yellowjacket traps or bait stations placed away from human activity. For nest removal near structures or when colonies are large, hire a licensed pest control professional because nests can provoke defensive swarming. In sensitive areas (beehives, crops, schools), professionals can apply targeted controls.

📍Where and when to find it

Look for foraging workers at flowers, fallen fruit, garbage, barbecues and meat scraps. Nests are commonly underground in rodent burrows, and sometimes in wall voids, attics or hollow logs.

✨Fun facts

• Western yellowjackets are both predators and scavengers — they help control pest insects but also compete with pollinators and can damage fruit crops by tearing fruit.
• In Hawaii Vespula pensylvanica readily forms large, multi-queen perennial colonies and is considered an invasive pest harming native ecosystems.
• Workers can sting multiple times and recruit nestmates with alarm pheromones, which is why disturbing a nest often leads to several wasps attacking.

?Frequently asked questions

📷Photos of the western yellowjacket