A unit of Lasting Forests
evolving since March 30, 1999
by Kenneth J. Stein, Ph.D., Conservation Management Institute, Virginia Tech, Blacksburg, Virginia 24061
On numerous occasions when I was doing research and placed ads in the local newspaper asking for yellowjacket and hornet nests, people would call me and say, "I don't know if I have yellowjackets but I think I have a nest of ground bees." Or they would ask me questions such as, "How can we remove the honey?"; "How did they build a nest on my house so quickly - within the past week?"; "What are they doing here?" During this time, I came to realize how little the public knew about yellowjackets. It was very apparent that most of these people confused yellowjackets with bees, and consequently, they had no knowledge of one of the most conspicuous parts of the insect life around them or, then, the important role that yellowjackets play. So why is this knowledge important? Does a yellowjacket population deep in the forest have an impact on the average person? Why do we need to know about yellowjackets, or any other insect for that matter?
Every day we seem to be bombarded with items in the news that suggest we have too many people, that too many of our natural resources are being threatened, and that our forests are in a state of decline. It also seems that whenever we hear the word "species," it is always preceded by one or more of the following terms: "rare", "threatened," and "endangered." These descriptive terms are bandied about in a way that knowledge of what constitutes a species implies some modicum of common knowledge. However, in the college freshman biology classes that I have taught, I have found that I am lucky if one or two students a semester can provide a textbook definition for what constitutes a "species." If most incoming college freshmen cannot adequately define "species,"
can we expect most of the public to know also? Furthermore, if the concept of species is not well-understood, do the terms "rare," "threatened," and "endangered" convey the correct message, if any?
If we examine yellowjackets (or any other insect species) in a forest ecosystem, we find that they have complex and interconnected relationships with all of the other inhabitants. We cannot satisfactorily examine the role of yellowjackets in a forest without examining these relationships, which help define their role. To put it more clearly, we don't know what would happen if the yellowjacket disappeared. It's an interesting question but only a mental exercise. Losing forests will surely cause yellowjacket losses but the reverse is unlikely. We can guess that a forest would be different without yellowjackets, but this is not the central point. Yellowjackets have a role; they have potential financial and health value, and we do not have to make moral or ethical claims, or appeals for their preservation. Perhaps learning what yellowjackets are, and, how they can be distinguished from bees is a good place to began addressing the above questions.
Bees are primarily nectar and pollen feeders, and they tend to be densely covered with fine hair which facilitates collecting pollen. Bees make their nests in a variety of locations including both living and dead trees, inside the stems of plants, and more commonly in the ground. Conversely, yellowjackets and hornets are wasps, not bees. In Europe the terms yellowjacket and hornet are seldom used; both are referred to as wasps. Like most wasps, yellowjackets and hornets are relatively bare-bodied. They are predators of many "pestiferous" insects, and they are also scavengers of human foods and carrion. While some adult yellowjackets will feed on nectar and pollen, this behavior is seen late in the season when their colonies are in decline and their preferred foods are not easily obtained. Unlike bees, they do not make honey, and neither do they store pollen or nectar. Depending on the species, yellowjackets make their nests in the ground, in both dead and living trees, and in human-made structures.
Bees In Virginia where I have done studies (but I presume most of the comments here will be relevant for the Mid-Atlantic area and beyond), there are several families of bees and their biology need a cursory review before we discuss the "yellowjackets."
The most well-known bee is the ubiquitous honey bee. Honey bees are not native to North America and the first colonies were brought here by the settlers. In fact, most honey bees in North America have an Italian ancestry. Historically the American Indians referred to the honey bee as the "white man's fly" and knew that where it was, the "white man" was not too far behind. Honey bees are golden-brown and black in color, and tend to be very hairy. They are highly-valued by farmers for their pollination capabilities and by beekeepers for their ability to produce honey. Honey bees are common in the forest and some researchers suggest that for every colony of bees kept by beekeepers there is one corresponding colony in the wild.
Bumble bees are also common in the forests and are among the first bees to emerge in the spring. Like the honey bee, bumble bees feed on pollen and nectar. These bees tend to be black and yellow and they nest in the ground, and in some odd locations such as the abandoned nests of mice and squirrels. Evidence suggests that the urine of these rodents serves as an attractant for nest-site location. Bumble bees are the only other bees (in Virginia) that produce honey which they store in small "honey pots." However, this honey differs both qualitatively and quantitatively from that of the honey bees and thus, is not harvested .
Carpenter bees resemble bumble bees but tend to be a little more robust in appearance. Carpenter bees can be observed flying around bare wood structures (e.g., split rail fences, cabins, barns, and picnic tables) in early spring as they attempt to locate suitable nesting sites. Carpenter bees are very territorial and will often fly aggressively towards you when you enter their territory; however, it is the male that usually "sizes you up" and he is harmless. Upon locating a nesting site, the female carpenter bee chews the wood in an effort to make her nest, a tube-like structure that may be from two to several inches deep. The hole which it chews in the wood is almost perfectly round (ca. 3/8-inch-1/2-inch dia.) and looks so neat as to suggest having been made with a wood auger. One was bored into a wheelbarrow handle at Peculiar Manor. The porch rail is a favorite place. This tube is then divided into of cells, within each of which is placed a pollen ball. When a sufficiently large pollen ball is placed into a cell, she lays an egg adjacent to it, seals the cell, and begins to make provisions for another cell within the same tube. As the eggs hatch into larvae, they consume the pollen balls, pupate, and become adults the following year.
Colletids are another group of bees that resemble small bumble bees and these make their nests of mud (plasterer bees) or they live in tunnels that they dig in the ground yellow-faced bees). Many species will often reuse the nests of other bees, making the appropriate modifications which they require. Yellowfaced bees are unique insofar as they secrete a cellophane-type of material which they use to line their nest cavity. Colletids too feed on nectar and pollen.
The andrenids are medium-sized bees that tend to be very hairy, grayish-tan or silver-gray in color, and have a somewhat flattened appearance. Like the other bees, andrenids are also pollen and nectar feeders. They can be seen flying and/or aggregating near their burrows along streambanks, drainage ditches, and base-ground slopes.
The megachilids look very much like the andrenids but do not appear "flattened;" they nest in similar locations and some species rescue the burrows abandoned by other bees. Megachilids are very common and several species cut circular pieces (3/8-inch diameter) from the leaves of many plants, including garden and ornamental plants, which they use to line their nest cavities. Megachilids also feed on pollen and nectar.
The halictids are among the smallest bees (1/4-inch long) found in North America and are usually dark brown or metallic green in color. These bees make their nests solitarily, or sometimes they live together in communities and work together as a group. The most common halictid encountered among forest clearings and fields is the familiar "sweat bee," which is dark brown in color. This bee is appropriately named because of its inclination to collect perspiration from people. It occasionally stings if disturbed, but the sting is not terribly painful. Like the other bees, this bee fills its nest with pollen and can be seen foraging from early spring and through early autumn.
Yellowjackets and bees are in the same taxonomic order, or group, the Hymenoptera. The literal translation of this Latin name means "married-wing," and refers to the tiny hooks (called hamuli) that couple the front and hind wings together. Though yellowjackets are in a family separate from the bees, they tend to be very different in their behavior and ecology. I have the feeling that most people think of species differences being of the magnitude of human racial differences. Not so with yellowjackets. The differences can be as great as between dogs and cats, and pines and oaks.
In Virginia there are 11 species of yellowjackets, in two genera, the Vespula and Dolichovespula. The European hornet, our only true hornet (not a yellowjacket), is also found in North America and it is in the genus Vespa . These wasps are in the family Vespidae, a name historically derived from the Latin word "vespillo", a person in ancient times who would take away the corpses of the poor for burial at night.
Most hornet and yellowjacket nests are cryptic and seldom noticed until branches are trimmed from a tree where there nest is located or a lawnmower is run over their ground nest. More commonly, when the autumn leaves fall, large hornet nests are revealed in trees and people gasp in amazement and comment, "I had no idea that there was such a large nest there." By this time, a typical nest has probably produced well over two thousand workers, several hundred males, and perhaps a similar number of queens.
In late summer and early autumn (well before the leaves have turned color) the male yellowjackets mate with the new queens. The former die and the latter seek hibernation sites (hibernaculae) in which to spend the winter. Typically, these hibernaculae are located inside fallen logs, under loose bark of dead trees, in woodpiles, under loose shingles, unusual places like inside the tarp of your fishing boat, and in the ground. The queen spends the winter in seclusion, and unless disturbed, remains in this hibernation site. A hibernating queen in your firewood pile (no matter how cold it is) brought indoors will become active within minutes and can sting. The queen relies solely on her energy reserves to sustain her during the hibernation period since she does not feed for at least nine months. During the hibernation period the queen loses slightly over 50% of her dry body weight.
Occasionally, queens will fly about on warm winter days. These queens are believed to return to their original hibernation site, though they often locate a new site. Sometimes these queens die by failing to return to a site before the onset of cold temperatures and become prey for birds, shrews, and mice. During this time many queens become susceptible to a variety of fungal and bacterial infections.
Although there is no experimental evidence, several theories suggest that a combination of temperature and day-length provide the cues for yellowjackets emerging from the hibernaculum in the spring. In my own research I have observed that many species make their appearance like clockwork in the spring, year after year. For example, the queen of one species might appear during the third week of April, another species begins to appear during the first week of May, and so on. Many queens have some type of physiological problem and never initiate nests. These queens can be seen flying about well into summer, that point in the life cycle when most queens remain "at home" in their nests.
As the yellowjacket queens emerge with their energy reserves depleted, they begin to feed on a variety of materials including honeydew, tree sap, floral nectar, and live insect prey. In the mountains of southwestern Virginia, I have seen them collecting nectar from blueberry and Russian olive, two of their favorite nectar sources. Similar to honey bees, perhaps yellowjackets "learn" where the best food source are. As an example, I once saw a small Virginia pine that had a small aphid infestation. As aphids feed, they excrete excess sugars and amino acids in a rich, nectar-like droplet referred to as honeydew. Honeydew had collected on the branches of this small tree, 7 feet high, and it had about 20 different queens attempting to collect these very nutritious secretions.
Shortly after emergence from hibernation, the reproductive organs of the spring queens begin to develop, and simultaneously, the queens attempt to locate suitable nesting sites. Upon locating a nesting site, the queen begins to form the first part of the nest, the pedicel. The pedicel, or point of attachment, is constructed from well-chewed wood fibers that are mixed with her salivary gland secretions. These secretions are probably as strong as some of our modern glues and are not water soluble. Though the pedicel is very small (3/8-inch long x 1/16-inch wide), it is also quite strong and will eventually support the weight of the queen and her immature nest. As the pedicel nears completion, more wood fibers are added to the tip of the pedicel, and from these, hexagonal nest cells are constructed. Simultaneously, a much thinner layer of these wood fibers, or nest paper, is placed around the entire structure. The nest resembles a small sphere at this point in the life cycle and is about 2/3 the size of a tennis ball. At this stage in the colony cycle the nest is referred to as an embryo nest.
Most queens build 20-45 cells during the embryo nest period, although the number of cells produced by queens of a given species are variable. The queen performs all duties during the period of nest initiation with major efforts devoted to nest construction, nectar foraging, and prey collection.
The queen will lay an egg in each of the cells, after a cell is partially built. These eggs hatch within several days giving rise to larvae which pass through five instars or stages. The larvae require insects or other arthropod prey for their development. The queen captures the prey and will chew it for some time before giving it to the larvae. The larvae chew the prey, ingest the nutritive parts, and discard the tough indigestible chitinous structures.
The hindgut is blocked during the larval stage and the larvae cannot excrete wastes in the usual manner. However, the larvae void water and excess free sugars and amino acids by special glands in their mouth. When the queen or worker returns from a foraging trip, she will nip the head of the larva to obtain a drop of these nectar-like secretions. She in turn will then give the larva the prey which she has collected. Some research has shown that if the queens are prevented from feeding on these secretions, the queen will not survive. Accordingly, colony survival is dependent on the reciprocal feeding arrangement between the larvae and adults.
After completing development in the fifth instar, or life stage, a larva spins a silken cocoon and then pupates. In a couple of weeks the new worker cuts the silk cap of its pupal cell and emerges as an adult. These workers take over the duties of the queen, and, for the rest of her life the queen stays in the nest and lays eggs.
The nest continues to grow by the addition of concentric rings of cells added to the periphery of the comb. Nest construction is a gradual process. Nest paper is removed from the internal paper envelopes, re-chewed, and then used to make new cells. Simultaneously, new paper is added to expand the outer envelope. The main function of these paper layers is to regulate the temperature and humidity inside of the nest. For example, in the nest of the bald-faced hornet the temperature is maintained at 84 degrees F and does not fluctuate with changes in ambient temperature.
A colony normally produces workers until a sufficient worker population is present, usually by mid-summer. It is at this time that the workers begin to construct cells for producing the parents of the next generation, new queens and males. Males are produced from unfertilized eggs laid by the queen. New queens, like the workers, develop from fertilized eggs and are apparently worker-larvae that are raised in bigger cells and are fed more food. While much of this process is not well-understood, we do know that the queen has control over which eggs become fertilized and which do not.
Yellowjacket Nest-site Location
The aerial yellowjacket and bald-faced hornet are two species that build their nests on the branches of trees, or on other structures such as walls, utility poles, etc. These species make their nest paper from wood that is weathered but still has some structural integrity. Other paper sources such as cardboard, paper cartons, and mulch are also used. The other yellowjacket species build their nests in the ground, often expanding an unused rodent burrow or decayed root passage. However, many species will build their nests inside structures such as wall voids. Deep in the forest I have seen several species nesting inside the walls of outhouses, ranger stations, and other sheltered areas. The nest paper of most yellowjackets is made from weathered and decayed wood, dead grasses, and the stems of other dead plants. The bald-faced hornet and aerial yellowjacket have relatively strong nests, whereas the nests of the other yellowjacket species tends to be very weak and brittle. Each species has a characteristic material that they prefer for constructing their nests. Most yellowjacket biologists who have worked with yellowjackets for awhile can recognize a species by the type of nest they make, much in the same manner as an ornithologist recognizes bird nests.
After the newly emerged queen and males mate in late summer or early autumn, the colony enters a state of decline. The male workers, and the foundress queen die, all having played their ecological role. The nest begins to decompose, a process which is facilitated by the elements and various scavenging insects, including flies, beetles, cockroaches, and moths. White-footed mice often eat the pupae and adults which have been killed by frost.
Many yellowjacket colonies do not reach maturity for a variety of reasons. In some cases, immature yellowjacket colonies are flooded and destroyed by spring rains. And as mentioned earlier, many of the solitary queen have important predators. However, even mature yellowjacket colonies are avidly attacked and eaten by skunks, raccoons, and bears. Where there are high skunk populations, the skunk may destroy up to 1/3 of nearby yellowjacket colonies. Predation by bears is very common as well. I have often seen the cavities (and the claw marks) created by the bears as they have excavated a huge yellowjacket nest. Some of these cavities are as deep or slightly deeper than a bushel basket. Hunters often attest to seeing the inside of the bear's stomach loaded with yellowjackets, larvae, and bits and pieces of their nests.
Yellowjackets and Hornets in Virginia
The European hornet came from Europe sometime between 1840 and 1860 and is found throughout Virginia (Table l); it has colonies that consist of several hundred workers. This hornet makes its nest inside hollow trees and occasionally inside of other structures, such as the walls of houses and barns; however, it is primarily a forest species. The European hornet has a brilliant appearance. It is golden-yellow and reddish-brown in color, and is about 1-inch to 1-1/4-inch long. It is a very powerful hunter and feeds on a variety of insects, including large grasshopper, crickets, and some very hard-shelled beetles. This hornet has a reputation for hunting at night and will often fly towards porch lights ,well-lit windows, and camp lanterns to search for prey. Occasionally this hornet damages trees by girdling small branches to collect sap. It also strips the skins of various fruits such as grapes, peaches, and apples to obtain the juices.
The most apparent of the yellowjackets is the bald-faced or white-faced hornet, and like the European hornet is found throughout Virginia. The reason I say most apparent is because this species constructs a large gray nest, the familiar target of some children (and adults) who feel obligated to test their throwing arm upon finding a nest. Although it is called a hornet it is actually a large yellowjacket. Most nests of the bald-faced hornet contain about 300-700 workers. This species is an exclusive predator of insects and its diet consists largely of flies. If you happen to stumble upon some carrion when you are hiking along a woodland trail, or driving along a road, you will often see these hornets nearby waiting in queue to pounce on flies. Once when I was cooking dinner in the mountains, it was a matter of minutes before the flies came and landed nearby waiting for the chance to take some food. Shortly thereafter, some bald-faced hornets landed nearby pouncing on these flies. This happened within two feet from where I was sitting. Like most foraging yellowjackets, the bald-faced hornet often dismembers its prey upon capture, cutting away the wings, legs, and other parts that are devoid of nutritive value. The prey is taken back to the nest, passed to the other workers, and chewed into a pulpy mass before it is given to the larvae. While the hornets prefer flies, they will prey on many insects including bees, crickets, grasshoppers, and even other yellowjackets. One of the most extreme examples of their hunting prowess comes from observations I made while watching a yellowjacket colony that was located inside the wall of a ranger station. Several of the bald-faced hornets learned the location of this nest and would hover there, attacking the yellowjackets as they flew in-and-out of the nest. Another time I was watching a German yellowjacket dismember a fly that it had captured. The bald-faced hornet attacked this yellowjacket, and flew away with it and the dismembered fly!
Another common yellowjacket in Virginia is the aerial yellowjacket or yellow hornet. Colonies of this species have between 200-700 workers when mature. It is found throughout most of Virginia; however, it is seldom found east of the Blue Ridge. Like the bald-faced hornet, the aerial yellowjacket constructs large paper nests and is usually among the first species to construct nests in the spring. As a corollary, this species is usually the first to reach maturity and typically dies out by the end of July or mid-August in Virginia. Most other yellowjacket nests remain active through the end of September, and even October. The aerial yellowjacket is an exclusive predator of many forest insects and like most yellowjackets, defends its nest readily if disturbed. As part of my research I used to collect a variety of yellowjacket colonies. At most nesting sites I would prepare a nest for live capture by trimming the branches from it, or examine its location during the day. Then at night I would cover the nest with a plastic bag and cut the supporting branch. Prior to the first time I did this, I had read accounts of the aerial yellowjacket being able to spray venom but did not take these seriously. One late summer afternoon I went to cut the branches from a nest and was immediately sprayed with venom. Even though I was wearing a protective bee-suit, the yellowjackets sprayed through the screened veil and I could not see very well for about 15 minutes. Likewise, I could not breathe normally for about 30 minutes and spent the next 1-1/2 hours coughing. The spraying of venom has two functions. It is both a repellent and it serves as a marker. If you do not run far enough from the nest, the attacking yellowjackets can smell the sprayed venom on you and continue their attacks. This sprayed venom has a very pungent and acrid smell.
Like other animals, yellowjackets have their parasites. Oddly enough, the most common of these is another black-and-white yellowjacket, Dolichovespula arctica, a species which has no common name. In the springtime, the queen of this species locates an immature nest of the aerial yellowjacket, and "moves in" with the host queen. Initially there is some antagonism between these queens; however, the host queen eventually accepts the parasite queen and becomes subordinate to her. The parasitic queen helps construct the nest and even helps tend the brood. As the workers of this nest begin to emerge from the pupal stage, they too accept the parasite queen. Eventually, when the colony is about one-third to mid-size, the parasitic queen kills the host queen and begins to lay her own eggs. Like the other yellowjacket queens, she no longer participates in nesting activities and is relegated to the role of an egg-layer. The workers begin to rear her brood that consists solely of males and queens. This parasitic species is the only species of yellowjacket in Virginia which has no workers of its own and produces only reproductives (queens and males). This unique relationship is somewhat similar to that of the cowbird which lays its eggs in the nests of other birds but does not take part in the rearing of her brood.
Dolichovespula norvegicoides is the only other yellowjacket that builds visible outdoor nests in southwestern Virginia. This species is found only at higher elevations, usually 3,500 feet and higher (e.g., Mountain Lake, Virginia, etc.) and west of the Blue Ridge. The biology of this species was recently described in Washington State and its colonies are slightly smaller in size than those of the aerial yellowjacket. Like the other Dolichovespula species, this species is an exclusive hunter of other forest insects.
Another black-and-white yellowjacket in Virginia is the blackjacket. This species is an exclusive predator of insects and spiders. Its colonies are very small, having at the most two hundred workers. The blackjacket is found throughout most of Virginia; however, it is typically not found east of the Blue Ridge. This species is most commonly found along fire roads and clear cut areas deep in the forests, and is one of the yellowjackets responsible for stinging episodes among loggers and firefighters. Although primarily a forest species, it occasionally resides in rural towns and villages. The blackjacket usually hunts close to the ground and its diet consists largely of spiders, daddy-long-legs, leafhoppers, planthoppers, caterpillars, and flies. It tends to hover and pounce on its prey, unlike the other species that spend a lot of time flying, inspecting each branch, etc. These distinct hunting strategies, locations, and times are referred to as resource partitioning and serve to illustrate the species difference discussed earlier.
Another yellowjacket which is quite common and has relatively small colonies is a species which has no common name, Vespula vidua. This species is found throughout Virginia with the exception of the Coastal Plain. Like the blackjacket, its colonies tend to be small, having at most 100-400 workers. Vespula vidua is found in the same environment as some of the other forest and woods species, near fire roads and other disturbed areas. However, it is also commonly found in rural towns and villages, meadows, and pastures. Vespula vidua is an exclusive predator of other insects and has not been observed to be a scavenger.
The most common yellowjacket in Virginia and probably the most aggressive is the eastern yellowjacket. The eastern yellowjacket is found throughout Virginia and makes its nest in a variety of locations such as clear-cut areas, fire roads, pastures, meadows, and those areas adjacent to campgrounds. Besides the imported German yellowjacket, the Eastern yellowjacket is probably the most abundant and often troublesome urban species. This species, unlike the others listed above, is both a predator and scavenger. It often has very large nests and by mid-summer may contain as many as 3,000-4,000 workers. In my own research I have watched them collect caterpillars, leafhoppers, planthoppers, cucumber beetles, daddy-long legs, ground and tree crickets, grasshoppers, flies, small moths, and carrion. The eastern yellowjacket is a voracious predator of the fall webworm and will often cut away the protective webbing of these caterpillars before attacking them. This species also relishes human and pet foods and sometimes becomes so numerous that they prevent people from eating out-of-doors. In addition, it is probably one of the most common yellowjackets encountered when dressing game or cleaning fish.
Another common yellowjacket found throughout Virginia is the southern yellowjacket. This species is similar in behavior and habits to the eastern yellowjacket and they also have very large colonies (1,000-4,000 workers). It shares the same disturbed habitats and urban locations as the eastern yellowjacket. However, the niches that they occupy in the forest are very different. The southern yellowjacket prefers pine and mixed forests, whereas the eastern yellowjacket tends to prefer hardwoods.
The southern yellowjacket queen is colored a dull, reddish-orange and differs from its workers that are yellow and black . The queen is very aggressive and will often destroy the queens of other species, especially queens of the eastern yellowjacket, and take over their nests. The workers of the host species exhibit some initial antagonism toward the usurping queen, but eventually the workers of the nest regard her as their own. She then produces offspring of her own which the eastern yellowjacket workers raise. It can be quite common to see mixed colonies of these two species. Unlike Dolichovespula arctica, the parasitic relationship of this species is not obligatory, but facultative.
The common yellowjacket, despite its name, is not as common or numerous as the other species in Virginia. It is found throughout most of Virginia, with the exception of the southern Piedmont and areas east of the Blue Ridge. Its colonies are slightly smaller (1,000-3,000 workers) than the southern or eastern yellowjacket and like these other species, it is a predator and a notorious scavenger. It feeds on a variety of forest insect pests including caterpillars, leafhoppers, planthoppers, flies, and crickets.
The hybrid yellowjacket is perhaps inappropriately named because it is not a true hybrid. Prior to its description as a new species in 1979, it was seen in insect collections, misplaced among similar looking species, and for this reason it was named "hybrid." The hybrid yellowjacket is both a predator and scavenger and is found throughout Virginia. Peak worker populations for this species are slightly smaller than the other scavenging species, perhaps 800-1,500 or slightly more. Like the other scavenging species it is often found in the urban environment and will construct its nest inside of human dwellings.
An Emerging Role for Yellowjackets?
What then is the role of the yellowjacket in the forests? Obviously they are very important predators and scavengers. Although research has not been conducted on the impact that yellowjackets have on an ecosystem, I would guess that a moderately-sized bald-faced hornet colony is going to collect hundreds of insects a day. Likewise, large yellowjacket colonies having thousands of workers are going to collect several hundred, and maybe a thousand insects (or more?) a day. The absence of these important predators would indirectly cause an overwhelming increase in the number of forest pests, largely the defoliators (caterpillars) and other plant-feeding insects (e.g., grasshoppers, crickets, planthoppers, leafhoppers, aphids, etc.). Although research has not been conducted on the impact that yellowjackets make on an ecosystem, studies have been conducted on its relative, the paper wasp, which has very small colonies (20-50 workers). Researchers in North Carolina showed that the placement of shelter boxes in tobacco fields encouraged the nesting of these wasps. This procedure resulted in higher than average wasp population and a 68% reduction in the number of caterpillars feeding on tobacco. Will similar beneficial aspects of yellowjackets and hornets in the forest environment be revealed someday?
What does the future hold for yellowjackets? I think that many scientists will eventually see the yellowjacket as an indicator species. Depending on the location and the type of species found there, these species will give people insight into the health of a local environment. For example, it is well-known that as an environment becomes more urbanized, the German yellowjacket becomes more apparent. Similarly, as forests change in composition (whether through normal successional processes or disturbances), so too will the distribution and composition of the yellowjacket species. Clearly, additional studies are needed to correlate the ecological profiles of yellowjacket with the condition of the forest.
Finally, in recent years we have found that many venom components are useful in treating individuals who experience allergic reactions to yellowjacket stings (referred to as immunotherapy). Correspondingly, each year there is an incremental increase in the number of components isolated from venom, as well as the knowledge of the biological properties of these. In one case, the venom of a South American stinging ant has been suggested as relieving the symptoms of arthritis. This has led to the culturing of these venom glands in the laboratory in an effort to harvest commercially the venom. Will the venom components of yellowjackets and other wasps reveal similar properties and perhaps, other medicinal uses?
It is apparent that yellowjackets have overlooked or potential beneficial roles in our environment. This might not be a consolation to you if they disrupt your lunch, fishing trip, hike, or otherwise keep you from enjoying the outdoors. However, they are an integral part of the forest and the human system. As common as they are, it is a wonder that so little is known about them.
Yellowjackets - Now What?
Within the emerging realm of resource management, we are continually confronted by new problems to solve. And, these problems are juxtaposed by major paradigm shifts occurring in both the university and government. Newer multi-disciplined problem solving approaches require an understanding of some of the newer research technologies and methods. Since more emphasis is being placed on these newer methods, it only follows that less emphasis would be placed on some of the traditional methods. Nowhere is this probably more apparent than in the areas of taxonomy (=systematics) and natural history.
Most entomologists would agree that taxonomy and natural history are integral components within the study of entomology; however, taxonomy is often viewed as one of those esoteric subdisciplines that should be reserved solely for the taxonomists. In some ways there is also a feeling that studies of insect taxonomy and natural history within the United States are complete. It logically follows that taxonomy, then, is given the same weight as other sub-disciplines such as physiology, morphology, behavior, etc. Indeed, today it is possible for a graduate student to get an advanced degree in entomology without having had a course, or, extensive training in taxonomy or biosystematics. Such a student might earn their degree working with one species of insect, and the focus of the degree is usually to study one or more processes (e.g., problems involving physiology, behavior, etc.). However, in an era when scientists and the public are continually confronted by this terms "species conservation" and "biodiversity," can we expect the above student to interact completely in these types of multi-disciplined research programs? Will such a student be pigeon-holed into performing a rote technique, with some minor variation thereof during his/her career? Would not such a student be better served by receiving an education, part of which emphasizes taxonomy and natural history studies? Would not their career opportunities, as well as the benefits to society be optimized by increased familiarity with these traditional studies?
An example of the importance of taxonomy and natural history comes from the recent studies with Lyme disease. When Lyme disease first emerged as a disease threat in the late 1970's, it was only a short while later that researchers described the epidemiology of this disease and its vector, the deer tick. It wasn't until 1993 that scientists reported that the deer tick was not a new species at all, but was conspecific with the black-legged tick (i.e., the deer tick and black-legged tick were the same species). Within this synonymization process, the researchers used a combination of both new and traditional methods to resolve this problem. What is the point? Traditional methods have a major role in modern science. However, it often takes a major problem to bring the necessity of these traditional methods forward.
A great deal of attention has recently been given to the concept of biodiversity. We want to conserve all species, a reasonable view, although it is doubtful that we well "know" all of them. It is, however, important to be able to identify them. If we cannot name an insect, we cannot adequately study its relationship with the other members of its community. Maybe X and Y insects will suffice in a classroom, but when we compare areas, or years, or treatments, we want to be sure that we are not mixing X, Y, and Z insects with some that are already very well-known, including their names and relationships. A textbook definition of ecology would suggest that ecology is the study of an organism's relationship to its environment. Does it not make sense that we have to be able to name an insect before we can begin to study its relationships? What affects insect X? What is the animal (or plant) affecting insect Y? The name is the intellectual hook on the wall. It is essential as the structure on which all science, all knowledge, is hung.
It is doubtful that any new yellowjacket species will soon be discovered in Virginia. Does this mean that we know all that there is to know about yellowjackets in Virginia and that we should abandon future studies? No, the study of yellowjackets is a minute subset of the described insect species of the world, estimated to be 1,000,000 species. What do we need to know about yellowjackets or any other insect for that matter? Knowing is not just nice, but necessary, in the new age of too many people, excessive use rates, and declining forests. It is very important to conserve the insects we now have ... even undescribed insects. I'm sure that we can find new species of insects in Virginia, never known to science. It may help in understanding the mechanisms involved in temperature regulation, winter survival, etc. Or, it may help us better understand a specific biochemical pathway that has previously been unreported.
When visiting with homeowners (>400 hundred) in my research during the last decade, I couldn't help but noticing how many people were interested in yellowjackets. These people watched as I removed their nests and made comments like "fascinating," "interesting," and "amazing." I would proceed to describe the biology and behavior of these wasps, which was then followed by a litany of questions from the homeowner. In fact, it was the rare exception when such a person was disinterested in these wasps ... they all had their own personal story to tell (e.g., running over a nest with a lawnmower, lighting a charcoal grill under a shade tree and learning the location of a nest). As is probably the case with most people, it usually takes a small problem of immediate concern, or something out of the ordinary, to spark an interest. This might include an unusual caterpillar on a favorite garden plant, a tick on one's pet dog, or a new bird at a bird-feeder. Taken to a larger scale, when an insect begins to affect society, that is when great interest is shown. Am I suggesting that we have a "management attitude" towards our problems? No; I merely illustrate in the above examples that most people have an inherent curiosity in the things that affect them, whether it affects them directly or indirectly.
As a proponent of natural history studies, it is my opinion that some of the best descriptions of insect biology, behavior, and habitat, comes from studies conducted prior to the 1970's. While many of the laboratory techniques and refined instrumentation of today was not available then, an emphasis was placed on the insect in its natural environment. There is now a tendency to view many of these earlier studies as "anecdotal" when these studies were not validated statistically; however, many brilliant observations were made during this time. Today, we still place an emphasis on the insect but oftentimes it appears to be studies of a single, or but a few processes. I am not disparaging the studies conducted today. Clearly, I have, and will continue to use the newer methods and instrumentation. I suggest that we should, perhaps, ensure that knowledge derived from modern techniques is coupled to the knowledge from the past. We should not view past studies as "anecdotal" or devoid of "meaningful" knowledge. Knowledge from these past studies should be woven together with the new knowledge. Every effort should be made to conserve this knowledge, much with the same emphasis we place on endangered or rare species. We need to keep our scientists as broadly trained as possible Insects, animals, and plants, as well as our other natural resources, are a major part of our national heritage.
|Table 1. Yellowjackets and Hornets in Virginia|
|European Hornet - Location: Throughout Virginia - Habitat: Forests and open woods. Exclusively predaceous on other insects and arthropods. On average it has small colonies of 200-400 workers, at the most 1,000 workers.|
|Bald-Faced Hornet - Location: Throughout Virginia - Habitat: Ubiquitous - urban, rural, and forest environments. Exclusively predaceous on other insects. Has moderately-sized colonies of 300-70s workers.|
|Aerial Yellowjacket - Location: Most of Virginia, though seldom found east of the Blue Ridge, the southern part of the Piedmont and Coastal Plain. Habitat: Ubiquitous, similar to the bald-faced hornet. Exclusively predaceous on other insects. Has moderately-sized colonies of 200-700 workers.|
|Dolichovespula arctica - Location: Found in the same locations and habitats as the aerial yellowjacket, its host A parasitic species producing only males and queens. Colony size depends on the strength of the host colony.|
|Dolichovespula norvegicoides - Location: Found west of the Blue Ridge and usually at higher elevations, 3,500 feet and higher. Habitat: Forests and clearings. An exclusive predator of insects and other arthropods. Has relatively small colonies of 150-300 workers.|
|Blackjacket - Location: Northern part of the Piedmont, the Blue Ridge and west. Habitat: Primarily a forest species; fire roads and clear cut areas. An exclusive predator of insects and other arthropods. Very small colonies of 100-200 workers.|
|Vespula vidua - Location: Throughout Virginia with the exception of the Coastal Plain. Habitat: Sometimes a forest species, near fire roads, and other disturbed areas, meadows, and pastures. An exclusive predator of other insects. Small colonies of 100-400 workers.|
|German Yellowjacket - Location: Throughout Virginia. Habitat: Primarily an urban-dwelling species. A predator of insects, but also a voracious scavenger. Extremely large colonies often containing thousands of workers.|
|Eastern Yellowjacket - Location: Throughout Virginia. Habitat: Ubiquitous - urban, rural, and forest environments; prefers hardwood forests. Both a predator and scavenger. Extremely large colonies often having 1,000-4,000 workers.|
|Southern Yellowjacket - Location: Ubiquitous throughout Virginia. Habitat: Forests, clearings, disturbed habitats and urban environments. Prefers pine and mixed forests. Both a predator and scavenger. A facultative parasite associated with other species, usually the eastern yellowjacket. Extremely large colonies of 1,000-4,000 workers.|
|Common Yellowjacket - Location: Throughout most of Virginia, to the Blue Ridge and west, not found in the southern Piedmont. Habitat: Forest edges, clearings, meadows, and pastures. Both a predator and scavenger. Moderate to large colonies of 1,000-3,000 workers.|
|Hybrid Yellowjacket - Location: Throughout Virginia except the southern part of the Piedmont and Coastal Plain. Habitat: Urban, rural, and forest environments. Both a predator and scavenger. Moderately-sizes colonies of 800-1,500 workers.|
An e-mail note was received on July 25, 2002:
I happened to see your website today, and I thought you might be interested in knowing that Vespula acadica (called "forest yellowjacket" by Akre) occurs between Grayson Highlands SP and Mt. Rogers. It has been found in Pendleton Co., WV, so it is likely to occur on the VA side near US 33. Whitetop Mt. would be another possibility but I haven't seen it there. It is also found in a few localities in western North Carolina.
The name "hybrid yellowjacket" was given to Vespula flavopilosa by Akre; no one probably ever called it anything but a "yellowjacket" before its description. Some people apparently feel that a common name must be tagged to every species (a practice perhaps encouraged by USDA?) whether or not anyone but the person assigning the name ever uses it!
Bob Jacobson, email@example.com
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