Technical Information - Pests

IPM for Yellowjackets and Hornets in Schools

Introduction - Identification and Biology - Stings - Nest Disturbance - Detection and Monitoring - Management Options - Physical Controls - Chemical Controls

Introduction

Yellowjackets and hornets are both beneficial and problematic wasps. They are important predators and scavengers, helping to control pests and recycle organic materials. Although often grouped together with bees, yellowjackets pose a more serious threat to people. Yellowjackets can sting repeatedly whereas a bee can sting only once. Multiple stings from yellowjackets are common because they aggressively defend their nest when it is disturbed.

Identification and Biology

"Yellowjacket" and "hornet" are the common names given to wasps in the genera Dolichovespula, Vespula, and Vespa; but for the sake of simplicity, we will use the term "yellowjacket" in the following discussion. Note that these common names are not reliable indicators of whether or not they are pests.

Yellowjackets are relatively short and stout with and hold their legs close to their body, compared with other wasps. Paper wasps, for example, are more slender and have long dangling legs. All yellowjackets are striped either black and white or black and yellow. They are rapid fliers, and are more aggressive than other types of wasps. Their nests are always enclosed with a papery envelope and can be found in the ground, hanging from eaves or tree branches, and occasionally in wall voids.

The queen yellowjacket begins her nest by building a small comb of chewed wood. She lays eggs in the cells and, after the eggs hatch, tends the larvae herself. Once the larvae develop into adult workers, they expand the nest into tiers, built one on top of the other. Yellowjacket colonies seldom exceed 15,000 workers with a single queen, although they can become larger and can include multiple queens in perennial colonies. In the late summer or early fall, new queens and males are produced. After mating, the queens seek a sheltered place to spend the winter and, except in perennial colonies, all the worker wasps die. The nest is not reused and eventually disintegrates. Early in the warm season, colonies are small and yellowjackets are usually not a problem. Later in the season when colonies are at their peak, these insects become pestiferous. In their search for protein and carbohydrate sources, they are attracted to garbage cans, dumpsters, lunch counters, and playgrounds, where they scavenge for food.

Stings

Insect stings are the leading cause of fatalities from venomous animals, and most of these stings are inflicted by honeybees. The people who die from yellowjacket or bee stings are people who experience large numbers of stings at once or who suffer severe allergic reactions to the inflammatory substances in the insect venom. These allergic reactions include soreness and swelling, not only at the site of the sting, but also on other parts of the body that may be distant from the site. Other symptoms include fever, chills, hives, joint and muscle pain, and swelling of the lymph glands and small air passageways. In severe cases, the individual may suffer a sudden drop in blood pressure and lose consciousness. While many individuals who experience allergic reactions have become sensitized over time by previous stings, half of all fatalities occur in individuals stung for the first time.

Non-allergic reactions to stings include localized pain, itching, redness, and swelling for hours to a day or two after the event.

Nest Disturbance

Yellowjackets that are foraging for food will usually not sting unless physically threatened, such as being struck or caught in a tight place. But if they feel their nest is in danger, they will vigorously defend it. All wasps defend their colonies, but some yellowjackets are more sensitive to nest disturbance and more aggressive in their defense. Disturbing a yellowjacket nest can result in multiple stings. This can occur when someone accidentally steps on an underground nest opening or disturbs a nest in a shrub or building. Sometimes merely coming near a nest, especially if it has been disturbed previously, can provoke an attack.

Wasps in underground nests can be disturbed simply by vibrations. Thus mowing lawns or athletic fields can be hazardous, and operators may need to wear protective clothing when mowing during the late summer season when colonies are large. It can be very frightening to be the victim of multiple wasp stings. The first response may be to run away, however the best strategy is to back slowly away from the colony until the wasps stop attacking you. It is important to educate children about the beneficial role of these wasps (they feed on pest insects, particularly caterpillars) and to remind them repeatedly of ways to avoid stings. Since problems with yellowjackets are most common in late summer and fall, teachers can be provided with this information at the beginning of the fall term. See tips on avoiding and treating stings.

Detection and Monitoring

If there is a chronic problem with yellowjackets around outdoor lunch areas or school athletic fields, inspect the area methodically to locate the nests. Nests can be found in the ground, under eaves, and in wall voids of buildings. Ground nests are frequently (but not always) located under shrubs, logs, piles of rocks, and other protected sites. Entrance holes sometimes have bare earth around them. Nest openings in the ground or in buildings can be recognized by observing the wasps entering and leaving.

Management Options

The objective of a yellowjacket management program should be to reduce human encounters with the wasps, but not to eliminate them from the entire area since they are beneficial predators of insects. The two most productive and least environmentally destructive ways to do this are to modify the habitat to reduce yellowjackets' access to food in the vicinity of human activities, and to use physical controls such as trapping and nest removal. Area wide poison-baiting should be used only as a last resort when other methods have failed and stings are frequent.

Physical Controls

Habitat Modification

Since garbage is a prime foraging/predation site for yellowjackets, garbage containers on school grounds should have tight fitting lids. The receptacles should be emptied frequently enough to prevent the contents from impeding the closure of the lid. The lids and containers should be periodically cleaned of food wastes. Disposable liners can be used and replaced when soiled or damaged.

When these practices are not followed, school garbage (and the flies around it) becomes a food source for yellowjackets in the area. With a large number of wasps around garbage containers, students may become afraid to get close enough to place garbage all the way inside, and spilled food attracts more wasps.

Dumpsters should be cleaned frequently by washing them with a strong stream of water. If the dumpster service company has a cleaning clause in their contract, make sure it is enforced. To limit yellowjacket infestations inside the school buildings, repair windows and screens and caulk holes in siding. Building inspections for yellowjackets can be done at the same time as inspections for other pests such as rats, mice, termites, etc. Inspections should be conducted monthly to ensure that developing nest are found before they get large enough to be problematic.

Trapping

Trapping with a sturdy trap and an attractive bait can significantly reduce yellowjacket numbers if a sufficient number of traps are used. There are a variety of traps on the market. In general, cone-type traps are more useful for long-term (many weeks) trapping. In some schools, unbaited yellow sticky traps (like those used to catch whiteflies) affixed to fences near underground nests have provided sufficient control to protect children from stings.

A homemade, cone-type fly trap can be used to catch yellowjackets simply by using the captured flies inside the trap as bait. The yellowjackets enter the trap to get the flies and become trapped themselves (see tips on this kind of trapping). You can also try using baits such as dog food, ham, fish, and other meat scraps, or, toward the end of the warm weather, sugar syrups, fermenting fruit, and jelly.

Take care to place traps out of the children's reach as much as possible. However, the traps should be placed near the nest if it can be found, and/or near the area where the yellowjackets are troublesome. Teachers can be instructed to make a short presentation on the purpose of the traps to satisfy the curiosity that students will undoubtedly have. Show students the traps, explain how they work, and try to impress upon them the importance of the traps in maintaining the safety of the playground.

When traps are full they can either be placed in a freezer for a day to kill the wasps or enclosed in a heavy-duty plastic garbage bag and placed in the direct sun for several hours. A third way of killing the wasps is by submerging the traps in a bucket of soapy water until the wasps drown.

The traps should be out only during the period that yellowjackets are a problem, usually late summer and early fall. When the traps are taken down for the year, they should be cleaned with soap and water and stored.

Nest Removal

A nest can be destroyed through physical removal (vacuuming) or by using a pesticide (see Chemical Controls). Either way, great care must be exercised because any disturbance around a nest can cause multiple stings. It is best to have a professional pest control operator (PCO) or other experienced person remove the nest. Nest removal should take place at night when the children are out of school and the yellowjackets are inside the nest. When illumination is needed, use a flashlight covered with red acetate film so it will not disturb the wasps.

Adequate protective clothing and proper procedure can minimize problems and stings. It is important to wear protective clothing when removing wasp nests. Complete body coverage is essential because yellowjackets and other wasps can find even the smallest exposed area. Use clothing made for beekeepers. This includes:

Vacuuming

Vacuuming is particularly effective when:

Vacuuming out entire nests is not recommended unless it is done by a PCO experienced in handling stinging insects.

In some cities there are pest control companies that will perform this service for free so they can collect the wasps to sell to pharmaceutical companies for their venom. If the school is interested in this, take time to find a reputable company.

Chemical Controls

If non-chemical methods alone prove insufficient to solve the problem, then integrating a pesticide into your management program may be warranted.

Pesticides must be used in accordance with their EPA-approved label directions. Applicators must be certified to apply pesticides and should always wear protective gear during applications. All labels and Material Safety Data Sheets (MSDS) for the pesticide products authorized for use in the IPM program should be maintained on file.

When an insecticide is considered necessary for the control of yellowjackets, the best approach is to confine it to the nest itself. Anyone applying insecticides should use special clothing that protects against the chemical as well as against wasp stings. Insecticides should be applied in the evening or very early morning when children are absent, the wasps are inside the nest, and cooler temperatures reduce insect activity.

A number of insecticides are registered for use against yellowjackets, the following are most appropriate for use in schools:

Dusts

Residual dusts can be very effective at controlling nests found in wall voids and underground nests. The extent of wall void nest should be determined by listening for activity behind the wall surface. Once the boundaries of the nest have been determined, holes can be drilled into the wall and an appropriately labeled residual dust can applied. The subsequent holes can be plugged with steel wool to prevent the wasps escape. Outdoor ground nests can be similarly controlled by approaching the nest at night and dusting the entrance; this procedure should be followed by plugging the entrance with dusted steel wool.

Silica Aerogel and Pyrethrins

Silica aerogel combined with pyrethrins is an effective insecticidal dust that can be used to destroy an underground nest or a nest in a wall void. Silica aerogel is made from sand and works by absorbing the outer waxy coating on insect bodies. Once this coating is gone, the insects cannot retain water and die of dehydration.

Products with Components That "Freeze" Wasps

Pyrethrins can be used to quickly knock down guard wasps at the nest entrance and to kill yellowjackets in an aerial nests when they must be destroyed in the daytime. These aerosol products are designed to project a stream of spray 10 to 20 feet and contain highly evaporative substances that "freeze" or stun the yellowjackets.

Do Not Use Gasoline

Gasoline should never be poured into underground nest holes. This dangerous practice creates a fire hazard, contaminates the soil, and prevents the growth of vegetation for some time. A ground application of gasoline poses greater harm to children and the environment than a yellowjacket nest.

Avoid Area-Wide Poisoning

Mass poisoning is seldom, if ever, necessary, and is expensive due to the labor involved in the frequent mixing and replacement of bait. The effectiveness of bait mixtures is also questionable, since the baits face considerable competition from other food sources that are more attractive to scavenging yellowjackets.


Edited by: Timothy C. McCoy, University of Florida.
Originally written by: S. Darr, T. Drlik, H. Olkowski, and W. Olkowski

Photographs and Graphics: University of Florida

Published: May, 1998


Return to Technical Information - Pests Menu