Yellowjackets

Take-Home Points:

• The southern yellowjacket, (Vespula squamosa), does not appear to be very prevalent in Massachusetts at this time. Further research could shed some light on their distribution in the state. Nonetheless, this species is recently receiving a lot of attention in the news. If you suspect you’ve seen one, you can report them here on iNaturalist .
• In general, conflicts between yellowjackets and people increase in the fall (August through September). This includes both native species, such as the eastern yellowjacket (Vespula maculifrons), and introduced species with a longer history and presence in the state (the German yellowjacket, Vespula germanica). This is because the number of yellowjackets per colony increases from spring through fall, with peak numbers occurring around late summer holidays, like Labor Day. They also like the same foods we like to eat outside at picnics and fairs – yellowjackets forage primarily for sugar at the end of the season. This is in contrast to earlier in the year, when foragers primarily hunt for insect protein. Yellowjackets are also attracted to overripe fruit left on plants.  
• If you encounter wasps while eating outdoors, the best practice is to let them help themselves to the food. Avoid swatting at them, as this could invoke defense behaviors. After they have gone, take precautions to cover, finish, or remove the food. 
• The presence of yellowjackets will cease as soon as we receive the first hard frost of the season. All the workers are killed at that time. Only a single queen will overwinter, and she will emerge next spring to begin her own colony.

What’s up with the Yellowjackets?

You may have recently seen some excitement in the news about yellowjackets (September 2024: southern yellowjackets in Massachusetts). Wasps are in the order Hymenoptera, which also includes bees, ants, and sawflies. Yellowjackets are members of the family Vespidae, which include social paper wasps and yellowjackets, for example, which form colonies and have different castes.  This family is also home to many solitary wasp species, and the majority of wasps worldwide are solitary.

  

Photos from left to right: adult female eastern yellowjacket (Vespula maculifrons, photo: Bruce Marlin). German yellowjacket overwintering queen (Vespula germanica, photo: Steve Jacobs, PSU Entomology). And southern yellowjacket adult female (Vespula squamosa, photo: Lyle J. Buss, University of Florida, IFAS).

Massachusetts is home to many insects in the family Vespidae, but recently the yellowjackets are receiving some attention. The eastern yellowjacket (Vespula maculifrons) is found in the eastern United States and is native to Massachusetts. A non-native yellowjacket, such as the German yellowjacket (Vespula germanica) was accidentally introduced to the temperate regions of the world, including eastern North America, in the 1970’s. Recent concern in the news is that the southern yellowjacket (Vespula squamosa), is becoming prevalent in Massachusetts. While it has been seen in our state, the reports are currently very infrequent. The historical range of the southern yellowjacket has been from Iowa to Texas and points east. It also extends southward into Mexico and Guatemala. 

Further research is necessary to determine the current distribution of the southern yellowjacket in Massachusetts and New England. It is thought that with mild winter temperatures due to climate change, it could be possible for this species and many other insects to expand their range northward. However, this is a very complex process that will take time to play out, and research to fully understand. Predicting changes in insect population distribution due to climate change is incredibly complex. Entomologists need to consider temperature, individual insect phenotypic and genotypic flexibility, and many other factors.

More about the southern yellowjacket

Nesting Habits:

The southern yellowjacket (Vespula squamosa) creates both ground  and aerial nests. Ground nests occur on or below the ground surface, and are the most common nesting strategy for southern yellowjackets. Aerial nests occur in trees or other structures, and may be found in unique areas, including stacked hay bales, wall insulation, or ceiling voids. 

The southern yellowjacket has been reported to produce massive nests – some of the largest reports from Florida indicate that they can reach 7-8 feet in width and depth. They create paper nests that contain comb, which also can be present in impressive amounts. The paper nest is created by chewed up plant-based fibers. They are fond of creating nests in disturbed habitats, like yards and roadsides. In fact, up to 60% of colonies have been reported from parks, picnic grounds, and golf courses in a study completed in Georgia and Western North Carolina.

Most nests are annual, meaning they die off when cold temperatures arrive. In southern states, some can survive year-round because of the warmer climate. For example, this happens in Florida and is why the colonies can grow so large in that state.

Biology:

Nests are started by a single female – a queen – which overwinters in protected locations. Nests grow throughout the spring and summer, and by the fall can contain up to 4,000 southern yellowjackets. Most of the individuals are smaller-sized workers, and reproductive males and females are produced by the colonies in the fall. Each colony has three castes – yellow and black workers that are approximately 3/8 inch in length; larger reproductive males are ¾ inch long and have a burnt orange color; and reproductive females are larger than both and orange.

A note about the eastern yellowjacket, Vespula maculifrons, whose queens are not as large as those of the southern yellowjacket, Vespula squamosa. The larger southern yellowjacket queen has an advantage over the smaller eastern yellowjacket queen because she often will take over the nest the eastern yellowjacket queens create in the spring. 

This is referred to as being a social parasite – the southern yellowjacket taking over the colony of the eastern yellowjacket. Some research has shown that southern yellowjacket queens will also fight each other for the colony as well – anywhere from 2-25 or more additional, dead queens were found upon dissecting a southern yellowjacket colony. Some are kicked outside, others are “papered” inside the nest envelope walls.

Coexisting with or managing Yellowjackets

Nuisance, Safety and Removal of Colonies: 

It is quite common for people to experience annoyance and sometimes unwanted stings from yellowjackets in the fall. This is the time of year where both native and non-native yellowjackets may exhibit aggressive behavior. They are particularly attracted to food that contains sugar and protein. Soft drinks, fruit, sandwiches – any picnic items. Stay still and do not swat at a yellowjacket if it is trying to taste your picnic food. Wait until it flies away and then either finish, cover, or remove the food from the area.

Yellowjacket colonies on private property can be a serious health and safety risk for individuals with allergies to wasp, bee, or hornet stings. If you or a family member has a known allergy, hire a pest management professional to remove the colony safely. Consult a physician for individual safety procedures for anyone with a known allergy.

Even if you do not have an allergy to these insects, there are some situations where the presence of a colony cannot be tolerated - such as in areas frequented by people (near doorways, walkways, garages, picnic tables, and other structures).

Like other yellowjackets, the southern yellowjacket can present a conflict with people if their colonies are formed in close proximity to where people are (either in landscapes or inside the walls of homes). If you are dealing with a large yellowjacket nest that is in a location that cannot be avoided (and thus left alone and coexisted with) by people, it is recommended that you hire a pest management professional to help you get rid of the colony. This is especially true of nests in buildings or walls.

Otherwise, if the nest is in an area unused by people, the best approach is to avoid them and leave them alone. The nest will die off at the first hard frost, all but the overwintering queens will die.

If you must get rid of a colony yourself, here are some basic safety tips: it is important to take precautions to avoid being stung. Wearing a beekeepers veil (if you have one) with protective clothing and working at night or dusk when temperatures are cooler and when these insects are less active, are two of the most effective precautions. Aerosol wasp and hornet sprays injected into the entrance hole are usually quick and effective, and are labeled for and can legally be used to kill a yellowjacket colony. However, if the insects are in a remote location and can be avoided - it is possible to live and let the yellowjackets do the same.

Tips to protect property managers (landscapers, arborists, tree climbers, and other professionals): 

• Be aware of the possibility for yellowjacket nests to be found in the ground, in stone walls, in shrubs and trees, in tree trunks and stumps, among piles of stone, beneath planters, in wood or lumber stacked outdoors, and in the walls and eaves of buildings. They may also be found near water, such as nearby pools or faucets.
• Unlike a honeybee, yellowjackets can sting repeatedly. 
• Wear light colored clothing since yellow jackets are attracted to brightly colored clothing and to dark clothing.
• Do not wear fragrances i.e. after-shave lotions, perfumes, hair products, etc, as these may attract the wasps.
• Keep a lid or cover on sweet beverages and other foods when working outdoors.
• Check work areas for nests before starting the job. Vibrations from equipment used outdoors can be enough to stir the wrath of yellow jackets.
• Have available a can of wasp and hornet spray (aerosols containing pyrethrin or other active ingredients) to apply to nests that are found near work areas. Remember, a MA pesticide license is required for application of general use products on properties you are working on (that you do not own).
• If a nest is disturbed, walk away slowly (rapid movements result in aggressive responses by yellow jackets) keeping your face covered with your hands.

Invasive species alert

Be on the Lookout for the Northern Giant Hornet:

If you see a suspicious vespid wasp, yellowjacket, or hornet there is interest in reports of the northern giant hornet, or Vespa mandarinia, and those can be sent to the Massachusetts Department of Agricultural Resources using their Report Pest Sightings page. Hornets are very similar in appearance to yellowjackets, however in the case of the northern giant hornet they are much larger: adult hornets are very large, with workers 1-1.5 inches long and queens up to 1.75 inches long. More information about the northern giant hornet can be found on MDAR's northern giant hornet Fact Sheet. This non-native insect is not currently known to Massachusetts, however is of concern due to the threat it poses to pollinators such as wild and managed honeybees.

References

Massachusetts Introduced Pests Outreach Project: Northern Giant Hornet
Nesting Biology of the Southern Yellowjacket, Vespula squamosa (Hymenoptera: Vespidae): Social Parasitism and Independent Founding (MacDonald and Matthews, 1984)
PennState Extension: German Yellowjackets
Report the Southern Yellowjacket on iNaturalist
Texas A&M Agrilife Extension Southern Yellowjackets
University of Florida IFAS Extension: Yellowjackets and Hornets

Authors

Tawny Simisky, Extension Entomologist, UMass Extension Landscape, Nursery & Urban Forestry Program
Nicole Bell, UMass Extension Educator III – Pollinators