Bug Day (22): Western Yellowjacket

July 28, 2021July 22, 2021

Western Yellowjacket worker (*Vespula pensylvanica)*

The fennel in many spots has reached the peak of its flowering, offering a bounty of pollen to all takers. One of the regulars is this Western Yellowjacket (Vespula pensylvanica). Judging by the pattern of notches on its abdomen, it’s a worker (a sterile female), not a queen or a male. It’s harvesting pollen to take back to the nest to feed the larvae. The nest may be a thousand feet away or more, and is probably located in an abandoned ground squirrel burrow.

A single fertilized queen that survived the winter, while all the males and workers perished, founded this nest in early spring. She built paper hexagons on the ceiling of the cavity and laid a few eggs, probably less than a dozen. As their sole support, she foraged widely and worked hard to feed the the larvae until they matured into workers. Then she retired to the nest and dedicated herself to laying more eggs, while her newly hatched worker females took over the foraging and feeding duties. Late in the season, she will lay eggs that hatch into males.

Some related wasp species feed on plants exclusively. Not the Western Yellowjacket. It loves pollen and nectar and all things sugary, but it’s also a hungry carnivore and a predator. It catches and kills caterpillars, aphids, spiders, and a range of other bugs. Not only bugs, but also barbecued chicken, hamburgers, dog food — any protein, alive or dead. Where it has a nest within foraging range, this wasp is a familiar nuisance at cookouts, picnics, sidewalk eateries, wherever humans gather to eat outdoors.

The yellowjacket is sometimes confused with the honeybee. They are about the same size and wear yellowish color patterns. But the body of the bee is hairy all over. The yellowjacket has some hair, not very dense, on its upper body, but its abdomen is smooth. Bees are not attracted to meat and are not a nuisance at barbecues. The females of bees and of wasps can sting, but the bee usually dies shortly after. Her stinger has barbs, and if it’s deeply embedded in skin, she can’t pull it out. It remains attached to her innards like an umbilical cord, and as she flies away she empties herself out and dies within minutes. The yellowjacket’s stinger does not have barbs; the female can sting many times without harm to herself. Neither bees nor wasps will sting unless they feel threatened.

In our climate, a yellowjacket nest may grow to several hundred individuals, but as the weather turns cool and wet in late fall, they will all die off, except for fertilized queens. These will overwinter in some nook or cranny, often in the bark of an evergreen tree, until it’s time to found a new colony in the spring. In warmer climates, notably Hawaii, the Western Yellowjacket forms colonies containing multiple queens and many thousands of individuals that live year round. There, they attack and decimate populations of native insects that are important pollinators of native plants, and they even swarm and kill newborn baby birds. These yellowjackets were brought to the Hawaiian islands hidden in shipments of Christmas trees from the West Coast.