Yellowjackets

and baldfaced hornets

The most numerous and well-known stinging insect is the yellowjacket. There are a variety of species, mostly colored yellow and black. Baldfaced hornets, despite the name, are large black and white yellowjackets that make nests with tiers of gray paper combs, wrapped inside a papery ball. Some nest in trees, others in structures, still others nest in rodent burrows and compost or leaf piles. Yellowjackets deliver painful stings and when crushed, their bodies release alarm pheromone to attract other workers. Colonies can grow to 5,000 workers or more by the end of the summer.

Biology and Behavior

Nearly all of the Vespid wasps build nests of paper they create from combining saliva with chewed wood and using the fiber (cellulose) paste to make paper walls and cells for raising each season’s brood. Nests vary in size and location, but are started by overwintering mated queens. Once the queen has raised a few workers, they take over the task of building and feeding, and the queen focuses on egg-laying. Only female wasps have stingers because a stinger is a modified ovipositor (egg-layer). Male wasps are among the last raised in a nest, and only function to mate with the new queens. Colonies begin small. Some Vespids are predatory, foraging for other insects throughout the summer to provide protein for the colony. Some are scavengers for protein and may also feed on animal carcasses and pet and human food, causing problems for people. Some species use both strategies.

Yellowjackets build multi-tiered nests wrapped and protected by layers of “envelope”, which makes the nest rounded. Some yellowjackets prefer nest building in voids such as hollows in trees, structural walls, abandoned animal burrows or rotting tree stumps. Others prefer aerial nests in trees or under the eaves of out-of-the-way buildings. Whether built in voids, in trees or on buildings, yellowjacket nests have the characteristic envelope. They are often overlooked until their activity draws attention or the nest is disturbed. It is important to understand that wasps have a role in the environment and most stinging incidents occur during accidental or ill-advised interaction. Many ‘bee-sting’ incidents are actually caused by wasps. Wasps can sting repeatedly, while honey bees sting only once, leaving the stinger in the flesh. Reactions vary, so be prepared. IPM for wasps help reduce the chance of interaction, protecting both this important insect and us.