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.

Scavengers or Predators

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.

Yellowjacket Nests

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.

What Do Yellowjackets Look Like?

Kinds of yellowjackets

Here are just a few of the many species of yellowjackets you might see in New York. 

Aerial yellowjacket

Dolichovespula arenaria

½”, 14mm. Black with yellow markings and yellow legs. These wasps build small round, gray paper nests in trees or attached to structures; nests house up to 1000 workers.

Bald-faced hornet

Dolichovespula maculata

5/8-7/8”, 16-22 mm. This black and white yellowjacket is large and builds aerial nests as large, gray oval masses. Colonies can grow to 800 or so workers.

Common yellowjacket

Vespula vulgaris

5/8-2/3”,17-20mm. Black and yellow markings, more black than yellow, with yellow legs. Nests most commonly in the ground.

Downy yellowjacket

Vespula flavopilosa

½” 14mm. Black and yellow markings, yellow legs. Nests in voids but colonies are generally less than a 1000 with a shorter season.

Eastern yellowjacket

Vespula maculifrons

½ inch, 14mm. Black and yellow markings with an anchor shape at the top of the abdomen and stripes on other segments, yellow legs, very common in the northeast. Colonies can become large, as many as 2000-3000 workers in more natural spaces such as stumps, and leaf or compost piles. Their nests tend to be close to the ground.

German yellowjacket

Vespula germanica

½-5/8”, 14-16mm. Black and yellow markings on each segment that look like thick yellow arrows pointing down, yellow legs, very common in the northeast. They build large colonies of as many as 5000 workers inside voids, structures, old cars, sheds and sometimes underground.

Ground hornet yellowjacket.

Vespula vidua

¾”, 21mm Black with yellow markings, yellow legs. Colonies are rather small—a few hundred—and have a shorter season.

Southern yellowjacket

Vespula squamosa

½”, 14mm. Queens are a very striking orange-brown color with black markings. Female workers and males are yellow and black, like German yellowjackets. Colony size varies widely, (500-4000) most often in ground voids in disturbed areas.

The queens begin nest building in spring. Unless they are near a doorway or an area used by people, we don’t see the activity until the nest is large and active.

Yellowjackets forage in gardens looking for insects to feed their young.

Later in summer, you might see them active around picnic foods, drinks, trash bins and compost piles. This is normal activity.

How Do I Manage Yellowjackets in the Landscape?

The best way to reduce problems is to prevent them. Learn to scout for signs of wasp activity in spring and early summer. For instance, simply hosing down the first signs of an aerial nest early in the season can be helpful. If you find a large nest which can’t be ignored, call a pest control expert, or your local cooperative extension.

Timeline for managing wasp and hornet problems

Monitor buildings and grounds for wasp and bee activity on a weekly or bi-weekly basis, on warm sunny days.

  • Where possible, destroy young yellowjacket nests shortly after they are started before there are numerous workers using a strong jet of water, a long pole or a low-risk pesticide.
  • Look for yellowjacket activity including colonies and foraging workers. Watch where they come and go to locate the nest entrance.

On a weekly basis, monitor buildings and grounds for wasp and bee activity in sunny weather. If needed, use traps baited with fruit punch or orange soda to draw wasps away from sensitive areas such as playgrounds.

If yellowjacket activity is high, search for an active colony nearby.

  • Follow foraging wasps and you might see where they are congregating around an opening or an aerial nest.
  • Tape off areas to keep people and pets away if the site is not in a direct path of food traffic.
  • Reduce attractiveness of an area (to scavenging wasps) by minimizing food and food trash when possible.
  • Consult an expert if you find an active colony that poses a stinging risk to people and pets.
  • Note where you find nests so you can make the sites unavailable, if possible, for the following season.

Yellowjacket nests can be hidden and difficult to treat. Pesticides can also agitate yellowjackets making them more dangerous. Here we demonstrate a pesticide-free way, vacuuming, to remove yellowjackets (video) and reduce danger from a nest in a structure.

Plan a prevention strategy for the following season. Raise awareness among your family and neighbors or building staff about how using IPM can reduce stinging insect risks for the following season. Seal holes and entryways where wasps have found entry into wall voids. Likewise, remove rotted wood, and fill in holes and compress soil in ground voids that hosted colonies the prior season. Fix flashing in eaves where wasps (and insects) can enter buildings.
Always have an action plan in place to care for people and animals who have been stung.