Upon returning home last Thursday, I noticed the silhouette of what I thought was a paper wasp on the inside of one of the garage windows. It turned out to be something more exciting than that. Here in eastern Kansas, it is the time when female social wasps of all sorts are founding new colonies, or at least seeking a place to set up housekeeping. This individual is no exception, but she also has a devious alternative strategy she can use.
I gently captured the wasp in a plastic vial. In better light she was instantly recognizable as a queen of the Southern Yellowjacket, Vespula squamosa. This species is not quite as common as other species in eastern North America, so it was nice to have a chance to see one up close and finally get some respectable images of those muted ochre and yellow colors. As beautiful as these wasps are, their biology is even more fascinating and somewhat frightening.
Southern Yellowjacket is sometimes an "inquiline," a facultative social parasite of other yellowjacket species, namely the Eastern Yellowjacket, Vespula maculifrons, but also the Widow Yellowjacket, Vespula vidua. That is to say that while Southern Yellowjacket can exist like any normal, free-living yellowjacket species with a queen, worker caste, and males and new queens at the end of the colony life cycle, it can also hijack the colony of another species for its own benefit of free labor. Conversely, an obligate social parasite cannot exist on its own. It must successfully usurp a host nest. Obligate social parasites have no worker caste, only queens and males (in the case of yellowjackets).
Competition for optimal, concealed nesting sites can be keen, so social parasitism may have evolved as one way to solve this problem. Eastern Yellowjackets typically nest in abandoned rodent burrows and similar cavities, but they can also nest in wall voids of human structures. It is telling that colonies of this species in disturbed habitats and urban and suburban locations appear to be the most vulnerable to being taken over by Southern Yellowjacket.
The Southern queen typically invades an embryonic nest of its host, dominating, evicting, or killing the resident queen. There may or may not be any host workers at the outset, but eventually the nest is converted entirely to Southern Yellowjacket workers. Evidence of the host remains in the differing architecture of the nest. Southern Yellowjacket is a significantly larger insect than Eastern Yellowjacket, so the cells in the paper combs of the nest differ accordingly.
A mature nest of Southern Yellowjacket, persisting into late autumn, may contain an average of 5,000 cells. That is a lot of wasps! Southern Yellowjacket is not inherently more aggressive than most other yellowjacket species in defense of their nest, but more workers means a greater response to disturbance. You may want to inspect your yard carefully before using any powered tools that could cause vibrations and spark a yellowjacket offensive.
Southern Yellowjacket ranges from the Great Lakes to the Atlantic coast south of New England, to Florida, and west to Iowa, Kansas, and most of eastern Texas. It also occurs in southern Mexico and Guatemala, making it quite literally our southernmost species of yellowjacket.
Sources: Akre, R.D., A. Greene, J.F. MacDonald, P.J. Landolt, and H.G. Davis. 1980. Yellowjackets of America North of Mexico. U.S. Department of Agriculture, Agricultural Handbook No. 552, 102 pp.
Kratzer, Chris Alice. 2022. The Social Wasps of North America. Frenchtown, New Jersey: Owlfly Publishing, LLC. 417 pp.