Yellowjackets are common, aggressive social wasps recognized globally for their distinct black and yellow markings. They belong primarily to the genera Vespula and Dolichovespula, found across the Northern Hemisphere. Whether yellowjackets are invasive depends entirely on the specific species and the geographic location. Their status ranges from native pests to established invaders, which determines their ecological and economic impact worldwide.
Identifying the Common Yellowjacket Species
The term “yellowjacket” encompasses many species, primarily those in the genus Vespula. These wasps are small, averaging 12 to 15 millimeters in length for workers, with a slender waist and a smooth, nearly hairless body. They create nests from a paper-like material made of chewed wood fibers, typically concealed underground or within structural voids.
Two species frequently discussed are the German yellowjacket (Vespula germanica) and the western yellowjacket (Vespula pensylvanica). The German yellowjacket is native to Europe, North Africa, and temperate Asia. Workers measure approximately 12 to 13 millimeters and are distinguished by a spade-shaped black mark on the first abdominal segment.
The western yellowjacket is native to western North America, ranging from Canada down to northern Mexico. This species is similar in size to the German yellowjacket but is identified by a continuous yellow ring around the eye. Both species are considered pests within their native ranges due to their scavenging habits.
Global Status: Defining Non-Native and Invasive Populations
A species is considered invasive only when it is non-native, successfully establishes a reproducing population, and causes demonstrable ecological or economic harm. The invasive problem arises when these species are accidentally introduced to regions where they lack natural predators or diseases to control their population size.
The German yellowjacket (V. germanica) is a globally successful invader, establishing significant populations across the Southern Hemisphere. It is a destructive non-native species in places like Australia, New Zealand, Chile, Argentina, and South Africa. These populations often form massive, perennial colonies that survive through the winter, unlike their typical annual life cycle in their native range.
The western yellowjacket (V. pensylvanica) provides a distinct example of insular invasion, primarily in the Hawaiian Islands. Introduced there in the late 1970s, the mild climate allows the wasps to bypass the annual colony die-off, leading to huge, multi-queen nests. These perennial colonies can reach enormous sizes, with some reported to contain up to 593,000 wasps. This ability to form hyper-colonies in a favorable climate is a major driver of its invasive success.
The Environmental and Economic Costs of Invasion
The establishment of invasive yellowjackets inflicts significant costs, particularly in isolated environments. Ecologically, these wasps are aggressive, generalist predators that exert pressure on native insect and spider populations.
Invasive yellowjackets also compete fiercely with native insectivores, including birds and other native wasps, for protein resources. The German yellowjacket targets a wide range of native arthropods, including flies, bees, and moths crucial for pollination. Furthermore, they act as nectar thieves, such as when V. pensylvanica feeds on the nectar of native ‘ohi’a trees in Hawaii, disrupting the plant-pollinator relationship.
The economic consequences can be substantial, affecting agriculture, tourism, and public health. Both invasive species scavenge aggressively, causing damage to soft fruits and vineyards, and they pose a direct threat to beekeeping operations by preying on honey bees. In Chile, the economic impact attributed to the German yellowjacket alone has been estimated to reach approximately $21 million annually, largely due to control costs and agricultural losses. The presence of numerous yellowjackets also negatively affects outdoor recreation and tourism, leading to reduced visitor numbers in affected areas.