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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.

roundish papery nest with numerous insects flying around it attached to building overhang
Yellowjackets will aggressively protect nests of these size.  Photo: NYSIPM. Click photo to see enlarged version.

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?

As part of the Family Vespidae (wasps and hornets), yellowjackets are a type of wasp that can vary in appearance but are generally striped in black with yellow or white. They are not fuzzy like bees, and they do not have the small obvious ‘waist’ of paper wasps, because the abdomen is blunt and close to the thorax. We’ll highlight only a few of the thirteen yellowjacket species:

yellow and black insect pinned to white background
Yellowjackets ‘body’ shape differs from the slender waisted paper wasp.  Photo: NYSIPM. Click photo to see enlarged version.

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. Generally, they forage for prey and don’t scavenge for protein but they can become a nuisance in late summer when foraging for sweets. They can be very aggressive when the nest is disturbed.

Bald-faced hornet. Dolichovespula maculata:

5/8-7/8”, 16-22mm. This black and white yellowjacket is large and builds aerial nests as large, gray oval masses. Colonies can grow to 800 or so workers. They can be a problem when built near human activity if the nest is disturbed, but as foragers and not scavengers for protein, they aren’t a widespread pest until late summer when they develop a taste for sugar in overripe fruits (figs, apples). For more information, see How to Prevent the Buzz—Sting—Ouch! of Bald-faced Hornets.

white and black insect pinned to white background
Bald-faced hornets are larger than most other yellowjackets.  Photo: NYSIPM. Click photo to see enlarged version.

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. They both forage and scavenge but are much less common than German and Eastern yellowjackets.

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. This species will forage and scavenge.

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. Colonies are active in the northeast from May through September. They forage and scavenge for protein for their young, and adults will consume nectar and fruit juices.

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. German yellowjackets are aggressive when disturbed. They can travel up to ¾ mile to forage and scavenge for food.

black and yellow insects with flat-top abdomens
German (left) and eastern (right) yellowjackets.  Photo: NYSIPM. Click photo to see enlarged version.

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. These ground hornets are foragers for insect prey but will occasionally scavenge.

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. Southern yellowjackets are “social parasites”, which means that queens will take over the already established colonies of Eastern yellowjackets by killing their queen and using the workers to raise the new queen’s eggs. These have been documented on Long Island but maintain a more southern range for now.

side view of a winged wasp with a black and yellow head and thorax, an orange and black abdobmen, and orange legs
Southern yellowjacket queen. Photo: NYSIPM. Click photo to see enlarged version.

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Why Should I Worry About Yellowjackets?

The occasional yellow jacket is not a concern. Gatherings of wasps that coincide with human gatherings can be problematic in late summer or fall. Your best bet is always to scout for places where a ground nest or a void in old wood or a structure could house a growing nest. Find nests before they become a full colony. Here are tactics to reduce wasp problems:

Avoid wearing perfumes, fragrant or flowery lotions, shampoos, conditioners and soaps. Avoid swatting at wasps, or squashing them; crushed wasps emit a scent that may attract nest-mates. Gently blow off, or brush off a wasp that has settled on you. Avoid walking barefoot in lawns with clover or other flowering weeds. Reduce the use of clover in lawns that will be frequented by foot traffic. To reduce flowering heads and therefore stinging insect visits, use a lawnmower to cut clover lawns the day before a scheduled event. Watch for signs of nests by wasp activity, and remember to look up into trees. Doing this, a tactic called scouting, in the late spring helps you find nests while their population is small. In spring and summer, look in areas of soft soil where grass is rarely mowed, and look for holes in the ground or holes in rotting wood. Wasps, and animals, tend to look for areas that appear to not have human activity, so be aware when cleaning areas on your property that have been dormant. This is especially true while using equipment like weed trimmers.

Never pour gasoline into a wasp nest—it is dangerous, illegal and causes environmental damage. Never attempt to burn a nest—it can get out of control and cause an angry swarm. Never block the entrance to a nest; trapped wasps will find another exit, and if it is in a wall void, they may find their way into the interior of a house. Any such activity will rouse their defenses. Never pour liquid insecticides into a ground nest—this is illegal and ineffective. Never rely on insect ‘fogger’ products to control wasps in an open space. If there is any concern about a wasp or bee nest, consult a professional pest management company or beekeeper.

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Why Do I Have Yellowjackets in My Yard?

Yellowjackets are everywhere and very adaptable to the built environment. 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.

yellow and black insect sitting on edge of dirty cup
Yellowjackets are always willing to join your late summer or fall picnic.  Photo: NYSIPM. Click photo to see enlarged version.

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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.

Here’s a timeline for best management against wasp and hornet problems:

Early spring through summer:

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

Late spring through summer:

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.

Late summer through fall:

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. See NYSIPM’s suggestions on yellowjacket trapping to reduce stings at public events. 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 and reduce danger from a nest in a structure.

Winter:

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.

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