Social Wasps and Bees in the Upper Midwest
Wasp is a general term referring to a group of related insects in the order Hymenoptera (wasps, bees and ants). Although some wasps are solitary, i.e. just one adult female per nest, this publication discusses social wasps, i.e. multiple individuals sharing one nest. Most social wasps belong to the family Vespidae (sometimes referred to as vespid wasps). There are three types of social wasps in the upper Midwest. Two groups, the yellowjackets and paper wasps, are very common. The third group, the true hornets, is not found in this area. Despite its name, a baldfaced hornet is actually a type of yellowjacket.
Similarly, there are social and solitary bees. The family Apidae contains some of the most familiar social bees. Honey bees and bumble bees are two commonly observed bees in the upper Midwest. Like social wasps, a colony will consist of many individual bees working together.
Wasps and bees are beneficial insects. Bees are particularly valuable because of their role in plant pollination, including many agricultural crops. Wasps also pollinate to a much lesser extent and are important because they feed on a wide range of insects, including many common garden pests. Both wasps and bees have the potential to sting although they will generally not bother people if they are left alone.
People often mistakenly call all stinging insects "bees." While both social wasps and bees generally live in colonies with queens and workers, they look and behave differently. It is important to distinguish between these insects because different methods may be necessary to deal with them if they are encountered.
Yellowjackets, including baldfaced hornets (Vespula and Dolichovespula spp.)
Yellowjackets (Vespula sp.) are approximately 1/2 inch long (they range in size from 3/8 to 5/8 inch long), are bright yellow with black lines, spots, triangles or diamonds on their abdomen (figures 1, 11, 13, and 22). Different species have different color patterns (there are about 14 species of yellowjackets in the upper Midwest). The body is hard and shiny with few hairs. At rest the wings fold into a narrow strip atop the abdomen. Yellowjackets are often misidentified as honey bees; they can be most easily distinguished by the lack of body hairs and their brighter yellow coloration compared to the more golden brown coloration of honey bees.
Baldfaced hornets (Dolichovespula maculata) are large, black insects about 7/8 of an inch long with white to cream-colored markings on the front of the head and at the end of the abdomen (figure 2).
Paper wasps (Polistes spp.)
Paper wasps are slender with long legs that dangle beneath their bodies when they fly and measure from 1/2 to 1 inch long. They are generally brown with yellowish markings (figures 3 and 7). The European paper wasp (P. dominula) is a species that was introduced into the U.S. in the 1970's and found in the Midwest in the 2000's. European paper wasps are black and yellow in coloration and resemble yellowjackets (figures 4 and 17).
Honey bees (Apis mellifera)
Honey bees are approximately 1/2 inch long. They are golden brown with thin black stripes on their abdomen. They are fuzzy in appearance; the thorax, especially, is covered with branches or plumose hairs (figures 5, 8, and 18). Part of each hind leg is flattened for collecting pollen. When not flying, their wings usually lay flat and unfolded atop their abdomen.
Bumble bees (Bombus spp.)
Bumble bees range in size from less than 1/2 inch to an inch and are very fuzzy in appearance. There are many different bumble bee species common in the Midwest. Most species have a black and yellow coloration although some species may be other colors as well. All bumble bees have a roundish shape (figures 6 and 21).
Yellowjackets and paper wasps capture a variety of insects, spiders, and other arthropods which they feed to their young (figure 7). They are beneficial because their food includes caterpillars, flies, crickets, and other pests. Adults feed primarily on sources of sugar, such as the juices of ripening and overripe fruits and honeydew (a sugary substance secreted by certain insects, like aphids). Paper wasps also feed on the nectar of flowers, yellowjackets infrequently do this. During late summer and fall, some species of yellowjackets become aggressive scavengers around human food and can be common outdoors where food or drinks are available.
Honey bees and bumble bees feed only on nectar (carbohydrates) and pollen (protein) from flowers (figure 8). Honey bees can sometimes be found visiting bird baths, puddles, and similar sources for water.
Yellowjackets and baldfaced hornets make nests from a papery pulp comprised of chewed-up wood fibers mixed with saliva. Their nests consist of a series of rounded combs stacked in tiers. These combs are covered by an envelope consisting of several layers of pulp (figures 9 and 10).
Yellowjackets commonly build nests below ground in old rodent burrows or similar cavities (figures 11 and 12). They can also locate their nests in other cavities, such as hollow logs and landscape timbers as well as in buildings in attics and wall voids (figures 13 and 14). Other yellowjackets, including baldfaced hornets, build aerial nests out in the open in places such as trees and under eaves of buildings (figures 9, 10 and 15). Yellowjacket and baldfaced hornet nests can number from several hundred to several thousand insects at their peak. Nests are used for just one season and not reoccupied the following season.
Paper wasps also build their nests with a papery pulp. They construct only one comb of cells without any protective envelope (figure 16, 17, and 18). These insects are sometimes known as umbrella wasps because of the shape of their nest. Paper wasps typically build nests under any horizontal surface and are commonly found on limbs, overhangs, building eaves, beams and supports in attics, garages, barns, sheds, and similar places. Paper wasp nests are generally small, often with under a dozen individuals, with a maximum numbers of about 100 wasps. Like yellowjackets, paper wasps do not reuse nests the following year. European paper wasps differ from other paper wasps in that they will also build their nests on vertical surfaces and in cavities; they can also reuse old nests (figures 17 and 18).
Honey bees make a series of vertical honey combs made of wax. Their colonies mostly occupy manufactured hives but they do occasionally nest in cavities in large trees, voids in building walls, or other protected areas (figures 19 and 20).
Bumble bee colonies are often located underground in deserted rodent nests or other cavities, in compost piles, and underneath objects on the ground. Some species will nest higher up in trees or wall cavities as well as in bird houses and bird nests (figure 21). Like honey bees, bumble bees construct cells made of wax.
All wasps and bees have a complete life cycle with egg, larval, pupal and adult stages. We usually only get to see the adults as the eggs and larvae are in the nests. The larvae of bees and wasps are white and typically look like grubs.
Yellowjacket and paper wasp colonies survive only one year, referred to as an annual colony. Queens are the only members of the colony that survive the winter. Newly produced and mated queens leave their old nests and search for protected sites in which to overwinter, such as under loose tree bark, old rotten stumps, or within buildings, such as under siding. In April or May, each queen becomes active with warmer weather and selects a suitable location and starts to construct her nest. Each nest is built from scratch each year while the previous year's nests are not reused (except for European paper wasp nests).
Queens start laying eggs and begin raising workers (sterile daughter offspring) as soon as possible. Once workers are produced, they take over the duties of enlarging and maintaining the nest, foraging for food and caring for the young while the queen functions only to produce more eggs. The queen lays a single egg in each hexagonal nest cell. Once the egg hatches the adults feed the larva pre-chewed insects. Prior to pupation the larvae spin a white silken cap over the cell.
A single paper wasp queen may start a nest or several queens may do so. When a small group of females establish a nest, eventually one becomes dominant and becomes responsible for laying eggs. The others assume duties for the upkeep of the nest and are joined later by newly produced workers. If the founding queen is killed, another queen will take over laying eggs.
By late summer, new queens and males are produced. Shortly afterwards, the colonies start declining as the queens stop laying eggs. Eventually new queens are produced. After mating, they fly off to search for places to spend the winter. The nest remains active until freezing temperatures (usually in the mid to upper 20°'s F) arrive killing the old queen and the workers. In the upper Midwest, even yellowjacket and paper wasp nests inside a building do not survive the winter. If they don't die from the cold, they will starve.
When new queens take refuge in buildings for the winter, they remain in their overwintering sites until the weather becomes warm enough for them to become active. This typically occurs in late winter or early spring. Because they are trapped indoors, this gives the impression that a nest is active within the building. Fortunately, this is not the case. While yellowjacket queens typically overwinter singly in a building, paper wasp queens are gregarious, i.e. often there are at least several queens present. However, this just means that this is where they have overwintered and not a site of an active nest. The only necessary control is to physically remove or crush them. You can also capture them and release them outdoors.
Bumble bees also have annual nests, i.e. they only survive one year. In the spring, each new bumble bee queen selects a nest site and starts a new colony. She may line the cavity with dry grass or moss (depending on the species) and then collects pollen and nectar to produce a stored food called "bee bread." Her first brood of offspring, (5 to 20), will all be workers (daughters) who take over the colony responsibilities of nest enlargement, food gathering and storage, and feeding and caring for the larvae. The queen continues to lay eggs throughout the summer. By late summer, new reproductive males and females (drones and queens) are produced. They mate on the wing and the fertilized females move to hibernation sites underground or possibly in the shelter of loose bark to lie dormant through the winter. The males and workers still in the colony die with the first hard freeze.
Honey bees have a complicated caste system with a queen and workers tending to perform different tasks within the hive depending on their age, such as cleaning, feeding young, making combs, and foraging for nectar. Similar to wasps, the queen lays a single egg in a comb. The egg hatches into a larva that is fed rich glandular secretions from the young bees' heads called brood food. When the larva is ready to pupate, a worker seals the cell for it. Once the adult worker emerges from the pupae she joins the hive workforce.
Honey bees are perennial insects with colonies that survive more than one year. Honey bee workers and queens survive the winter by forming a cluster when hive temperatures approach 57° F. As the temperature drops, the cluster of bees becomes more compact. Bees inside this mass consume honey and generate heat so that those in the cluster do not freeze. As long as sufficient honey stores are available in the nest, a strong colony can withstand temperatures down to -30° F. or lower for extended periods.
When a colony gets too crowded it essentially reproduces itself by swarming. A colony produces a new queen and the old queen takes off with many of her workers. Swarming is an advantage to the bees but is a distinct disadvantage for beekeepers. Consequently, beekeepers manage hives to reduce the incidence of swarming to the largest extent possible. Swarming usually occurs in late spring and early summer and begins in the warmer hours of the day.
Honey bee swarms may contain several hundred to several thousand worker bees, a few drones and one queen. Swarming bees fly around briefly and then cluster on a tree limb, shrub or other object (figure 22). Clusters usually remain stationary for an hour to a few days, depending on weather and the time needed to find a new nest site by scouting bees. When a suitable location is found for a new colony, such as a hollow tree, the cluster breaks up and flies to it.
Honey bee swarms are not dangerous under most circumstances. Swarming honey bees do not have a nest to defend and bees away from the vicinity of their nest (offspring and food stores) are less defensive and are unlikely to sting unless provoked.
In most situations when a honey bee swarm is found hanging in a tree, shrub or house you do not need to do anything. Swarms are temporary and the bees will move on if you patiently ignore them. Stay back and keep others away from the swarm, but feel free to admire and appreciate the bees from a safe distance. Only if a serious health threat is present because of the location of the swarm, such as in a highly traveled public area, should you need to do anything with a cluster.
An experienced beekeeper may be willing to gather a swarm and relocate it for you. To find a beekeeper that is willing to remove a honey bee colony or swarm in Iowa, Minnesota, and Wisconsin, visit this bee removal website. If the honey bees are in Minnesota, another option is to look for a beekeeper on the Minnesota Hobby Beekeepers Association website.
Wasp and bee stings
Social wasps and bees sting to defend their colony. Some yellowjacket species can also become aggressive during late summer and fall and may sting unprovoked. Stinging involves the injection of a protein venom that causes pain and other reactions.
Yellowjackets, paper wasps and bumblebees can sting more than once because they are able to pull out their stinger without injury to themselves. If you are stung by one of these insects, the stinger is not left in your skin.
Honey bees have tiny barbs on their stinger that remain hooked in the skin. The stinger, which is connected to the digestive system of the bee, is torn out of the abdomen as the bee attempts to fly away. As a result, the bee soon dies. If you are stung by a honey bee, scratch out the stinger (with its attached venom gland) with your fingernail as soon as possible. Do not try to pull out the stinger between two fingers. Doing so only forces more venom into your skin, causing greater irritation.
Most people have only local reactions to wasp and bee stings, although a few may experience more serious allergic reactions. Local, nonallergic reactions range from burning, itching, redness, and tenderness to massive swelling and itching that may last up to a week. These local reactions can be treated with ice or commercial topical ointment to relieve the itching. An allergic reaction may include hives or rash, swelling away from the sting site, headache, minor respiratory symptoms, and stomach upset. These allergic reactions are not life-threatening and can be readily treated with an antihistamine. However if this occurs, seek medical attention.
(Very) rarely/occasionally, a person may suffer a life-threatening, systemic allergic reaction to a bee or wasp sting, which can cause anaphylactic shock (fainting, difficulty breathing, swelling, and blockage in the throat) within minutes of being stung. These systemic symptoms are cause for immediate medical attention. People with known systemic allergic reactions to bee or wasp stings should consult with their physician to obtain an Epi-Pen™ or Ana-Guard Sting Kit™ to carry with them at all times. The venoms of bees and wasps are different, so having a severe reaction to a bee sting does not automatically mean a person will have the same reaction to a yellowjacket or paper wasp sting.
Nests on your property
Yellowjackets and paper wasp nests
If a nest is located in an out of the way location and is unlikely to be disturbed, it is best left alone and ignored. If, however, a nest is located in a "high traffic" area such as along walks or near doorways, control is justified to reduce the threat of being stung. Yellowjackets and paper wasps are very protective of their colonies and will defend them if they feel threatened.
If a yellowjacket or paper wasp nest is present and you want to control it, keep a few things in mind. First, treat the nest during late evening or early morning when the yellowjackets are less active; this will help minimize the chance of stings. When treating the nest, wear protective clothing, i.e. a long-sleeved shirt and trousers; tie sleeves and pants legs shut or pull your socks out over your pant cuffs. If after a day there is still activity, i.e. yellowjackets or paper wasps are still flying back and forth, then repeat the treatment. If you are uncomfortable treating a yellowjacket nest, it is always an option to hire a pest management professional to deal with it; they have the experience and the appropriate tools to expertly eliminate nests. Do not attempt to manage a nest yourself if you are allergic to stings.
If you can see the nest, e.g. it is attached to the eaves; you can treat it using an aerosol spray labeled for "wasps and hornets" or something similar. These typically contain active ingredients such as tetramethrin or prallethrin. For yellowjackets, spray it directly into opening of the nest (where the yellowjackets fly back and forth). For paper wasps, spray them so all of the combs receive some insecticide. It is also possible to kill paper wasps with a soap and water mixture.
Yellowjacket ground nests
Nests in the ground can be controlled by placing an insecticide dust, typically containing permethrin, in and around the nest entrance during the night. The dust particles will adhere to the insects as they leave and reenter the nest and control will usually be achieved within a few days. Pouring a liquid insecticide into the nest entrance is less likely to be effective as the liquid may not reach the nest depending on where it is located within the burrow.
Concealed yellowjacket nests
Yellowjacket nests that are found inside homes in wall voids, attics, concrete blocks, or similar spaces are much more challenging to control. The most effective treatment is with an application of a dust, e.g. containing deltamethrin. Unfortunately, there are not many products like this available to the general public that are registered for use in buildings. An aerosol insecticide is not very effective. In fact, an aerosol spray can sometimes cause yellowjackets to look for another way out, which often leads them to the inside of homes. Also, don't seal the nest opening until you know all of the yellowjackets are dead as this can also cause yellowjackets to move into your house. It is usually best for a pest management professional to control hidden nests in buildings.
Honey bee nests
Honey bee colonies are infrequently found in buildings in wall or attic voids. While yellowjacket colonies are annual and do not survive winters, honey bee nests may last for many years. If a honey bee nest is suspected, capturing a specimen or taking a good picture and getting it identified is an important step to verify what insect is actually present.
If the specimens are confirmed to be honey bees, first consider contacting a beekeeper for help with removal of the colony. An experienced beekeeper may be willing to gather a swarm and relocate it for you. To find a beekeeper that is willing to remove a honey bee colony or swarm in Iowa, Minnesota, and Wisconsin, visit this bee removal website. If the honey bees are in Minnesota, another option is to look for a beekeeper on the Minnesota Hobby Beekeepers Association website.
If it is not possible to salvage a honey bee colony, then it may be necessary to treat it with an insecticide. If possible, wait to treat it until early spring, March to April. At that time the colony may be either dead, or if alive will have little honey left. This is the best time to treat the honey bees and remove the nest. Even if honey combs cannot be removed chances are there will be very little, to no, honey left in combs by April. By late April or early May honey bees start collecting nectar again, so there is a narrow window of time to remove them when there is little to no honey. Any remaining wax should not be a problem as wax moths usually destroy it quickly and then are gone. However, any combs and honey that may still be present can potentially cause a problem from bees from other colonies, scavenging insects and mice. Do not salvage these honey combs or honey if the colony was treated with insecticide.
Bumble bee nests
If the vicinity of a bumble bee nest can be avoided, leaving them alone and waiting for them to die in the fall is the preferred "management" option. Most species are not aggressive even when you reach directly into the nest or step on it and they are only active until September. Put up a little fence around the nest to help prevent accidents. Live-trapping bumble bees for relocation is not practical and covering the nest entrance does not usually solve the problem. Relocating the entire nest also is not practical as often the colony does not survive.
Bumble bee nests in yards, flowers beds, wood piles, walls or other areas where a lot of human activity occurs may create an unacceptable nuisance. If there is a high risk of stings and the area cannot be avoided, it may be necessary to treat the nest. Determine the exact location of the nest entrance from a safe distance during the day, but wait until night to treat if possible. Wear long-sleeved shirt and trousers and tie sleeves and pants legs shut or pull your socks out over your pant cuffs. Use a soapy water solution (about ¼ cup of laundry or dish soap to one gallon of water). Or if using an insecticide, treat the same as when treating ground-nesting yellowjackets.
Yellowjackets during late summer and fall
Late summer and fall is the time of year when populations of yellowjackets (often mistakenly called "bees") and other social wasps become large and noticeable. The wasps have been present since spring, but because colonies start as a single queen, populations are very small through the early part of the summer. Yellowjacket wasp populations peak during later summer when each nest may have up to approximately 5,000 wasps.
Some yellowjacket species become aggressive scavengers and can disrupt outside activities where food or drink are served (figure 23). Control of scavenging yellowjackets is difficult, as there are no insecticides that effectively repel or discourage them. It is possible to spray soapy water on individual yellowjackets to kill them.
Jeff Hahn, University of Minnesota
Fig. 23 Yellowjackets can be found around food and beverages during late summer and fall
The best strategy is to minimize attracting them.
- Wait to serve food and drink until people are ready to eat.
- Promptly put away food when done and throw garbage into a container with a tightly fitting lid.
- Examine glasses, cans, and other containers before drinking from them to check for yellowjackets that may have flown inside. If a yellowjacket flies into your food, wait for it to fly away or gently brush it away.
- If only a few yellowjackets are bothering your activity, ignoring them or capturing them with a net and crushing them may be sufficient.
- Traps may catch many wasps, but not enough are captured to noticeably reduce their activity in the fall.
The information given herein is supplied with the understanding that no discrimination is intended and no endorsement by the University of Minnesota Extension, Iowa State Extension, or the University of Wisconsin Extension. Mention of a pesticide or use of a pesticide label is for educational purposes only.
A pesticide label is a legal document. Always follow the pesticide label directions attached to the pesticide container you are using. Pesticide labels may change frequently. Internet labels may not match the label on the container you are using. The site of use or plant to which the pesticide is to be applied must be listed on the label or the pesticide cannot be used. Remember, the label is the law.