The term wasp is typically defined as any insect of the order Hymenoptera and suborder Apocrita that is neither a bee nor ant. Almost every pest insect species has at least one wasp species that preys upon it or parasitizes it, making wasps critically important in natural control of their numbers, or natural biocontrol. Parasitic wasps are increasingly used in agricultural pest control as they prey mostly on pest insects and have little impact on crops.
 
The majority of wasp species (well over 100,000 species) are "parasitic" (technically known as parasitoids), and the ovipositor is used simply to lay eggs, often directly into the body of the host. The most familiar wasps belong to Aculeata, a division of Apocrita, whose ovipositors are adapted into a venomous sting, though a great many aculeate species do not sting. Aculeata also contains ants and bees, and many wasps are commonly mistaken for bees, and vice-versa. In a similar respect, insects called "velvet ants" (the family Mutillidae) are technically wasps.
 
The suborder Symphyta, known commonly as sawflies, differ from members of Apocrita by lacking a sting, and having a broader connection between the mesosoma and metasoma. In addition to this, Symphyta larvae are mostly herbivorous and "caterpillarlike", whereas those of Apocrita are largely predatory or parasitoids.
 
A much narrower and simpler but popular definition of the term wasp is any member of the aculeate family Vespidae, which includes (among others) the genera known in North America as yellowjackets (Vespula and Dolichovespula) and hornets (Vespa); in many countries outside of the Western Hemisphere, the vernacular usage of wasp is even further restricted to apply strictly to yellowjackets (e.g., the "common wasp").
 
The various species of wasps fall into one of two main categories: solitary wasps and social wasps. Adult solitary live and operate alone, and most do not construct nests (below); all adult solitary wasps are fertile. By contrast, social wasps exist in colonies numbering up to several thousand strong and build nests—but in some cases not all of the colony can reproduce. In the more advanced species, just the wasp queen and male wasps can mate, whilst the majority of the colony is made up of sterile female workers.
 
The following characteristics are present in most wasps:
 
Two pairs of wings (except wingless or brachypterous forms in all female Mutillidae, Bradynobaenidae, many male Agaonidae, many female Ichneumonidae, Braconidae, Tiphiidae, Scelionidae, Rhopalosomatidae, Eupelmidae, and various other families).
An ovipositor, or stinger (which is only present in females because it derives from the ovipositor, a female sex organ).
Few or no thickened hairs (in contrast to bees); except Mutillidae, Bradynobaenidae, Scoliidae.
Nearly all wasps are terrestrial; only a few specialized parasitic groups are aquatic.
Predators or parasitoids, mostly on other terrestrial insects; most species of Pompilidae (e.g. tarantula hawks), specialize in using spiders as prey, and various parasitic wasps use spiders or other arachnids as reproductive hosts.
Wasps are critically important in natural biocontrol. Almost every pest insect species has at least one wasp species that is a predator or parasite upon it. Parasitic wasps are also increasingly used in agricultural pest control. Wasps also constitute an important part of the food chain.
 
In wasps, as in other Hymenoptera, sexes are significantly genetically different. Females have a diploid (2n) number of chromosomes and come about from fertilized eggs. Males, in contrast, have a haploid  number of chromosomes and develop from an unfertilized egg. Wasps store sperm inside their body and control its release for each individual egg as it is laid; if a female wishes to produce a male egg, she simply lays the egg without fertilizing it. Therefore, under most conditions in most species, wasps have complete voluntary control over the sex of their offspring.
 
Anatomically, there is a great deal of variation between different types of wasp. Like all insects, wasps have a hard exoskeleton covering their three main body parts. These parts are known as the head, mesosoma and metasoma. Wasps also have a constricted region joining the first and second segments of the abdomen (the first segment is part of the mesosoma, the second is part of the metasoma) known as the petiole. Like all insects, wasps have three sets of two legs. In addition to their compound eyes, wasps also have several simple eyes known as ocelli. These are typically arranged in a triangular formation just forward of an area of the head known as the vertex.
 
It is possible to distinguish between genders of some wasp species based on the number of divisions on their antennae. Male yellowjacket wasps, for example, have 13 divisions per antenna, while females have 12. Males can in some cases be differentiated from females by virtue of having an additional visible segment in the metasoma. The difference between sterile female worker wasps and queens also varies between species but generally the queen is noticeably larger than both males and other females.
 
Wasps can be differentiated from bees, which have a flattened hind basitarsus. Unlike bees, wasps generally lack plumose hairs.
 
Generally wasps are parasites or parasitoids as larvae, and feed only on nectar as adults. Many wasps are predatory, using other insects (often paralyzed) as food for their larvae. A few social wasps are omnivorous, feeding on a variety of fallen fruit, nectar, and carrion. Some of these social wasps, such as yellowjackets, may scavenge for dead insects to provide for their young. In many social species the larvae provide sweet secretions that are fed to the adults.
 
In parasitic species, the first meals are almost always provided by the animal that the adult wasp used as a host for its young. Adult male wasps sometimes visit flowers to obtain nectar to feed on in much the same manner as honey bees. Occasionally, some species, such as yellowjackets, invade honey bee nests and steal honey and/or brood
With most species, adult parasitic wasps themselves do not take any nutrients from their prey, and, much like bees, butterflies, and moths, those that do feed as adults typically derive all of their nutrition from nectar. Parasitic wasps are typically parasitoids, and extremely diverse in habits, many laying their eggs in inert stages of their host (egg or pupa), or sometimes paralyzing their prey by injecting it with venom through their ovipositor. They then insert one or more eggs into the host or deposit them upon the host externally. The host remains alive until the parasitoid larvae are mature, usually dying either when the parasitoids pupate, or when they emerge as adults.
 
The type of nest produced by wasps can depend on the species and location. Many social wasps produce paper pulp nests on trees, in attics, holes in the ground or other such sheltered areas with access to the outdoors. By contrast solitary wasps are generally parasitic or predatory and only the latter build nests at all. Unlike honey bees, wasps have no wax producing glands. Many instead create a paper-like substance primarily from wood pulp. Wood fibers are gathered locally from weathered wood, softened by chewing and mixing with saliva. The pulp is then used to make combs with cells for brood rearing. More commonly, nests are simply burrows excavated in a substrate (usually the soil, but also plant stems), or, if constructed, they are constructed from mud.
 
The nesting habits of solitary wasps are more diverse than those of social wasps. Mud daubers and pollen wasps construct mud cells in sheltered places typically on the side of walls. Potter wasps similarly build vase-like nests from mud, often with multiple cells, attached to the twigs of trees or against walls. Most other predatory wasps burrow into soil or into plant stems, and a few do not build nests at all and prefer naturally occurring cavities, such as small holes in wood. A single egg is laid in each cell, which is sealed thereafter, so there is no interaction between the larvae and the adults, unlike in social wasps. In some species, male eggs are selectively placed on smaller prey, leading to males being generally smaller than females.
 
The nests of some social wasps, such as hornets, are first constructed by the queen and reach about the size of a walnut before sterile female workers take over construction. The queen initially starts the nest by making a single layer or canopy and working outwards until she reaches the edges of the cavity. Beneath the canopy she constructs a stalk to which she can attach several cells; these cells are where the first eggs will be laid. The queen then continues to work outwards to the edges of the cavity after which she adds another tier. This process is repeated, each time adding a new tier until eventually enough female workers have been born and matured to take over construction of the nest leaving the queen to focus on reproduction. For this reason, the size of a nest is generally a good indicator of approximately how many female workers there are in the colony. Social wasp colonies often have populations exceeding several thousand female workers and at least one queen. Polistes and some related types of paper wasp do not construct their nests in tiers but rather in flat single combs.
 
Wasps do not reproduce via mating flights like bees. Instead social wasps reproduce between a fertile queen and male wasp; in some cases queens may be fertilized by the sperm of several males. After successfully mating, the male's sperm cells are stored in a tightly packed ball inside the queen. The sperm cells are kept stored in a dormant state until they are needed the following spring. At a certain time of the year (often around autumn), the bulk of the wasp colony dies away, leaving only the young mated queens alive. During this time they leave the nest and find a suitable area to hibernate for the winter.
 
After emerging from hibernation during early summer, the young queens search for a suitable nesting site. Upon finding an area for their colony, the queen constructs a basic wood fiber nest roughly the size of a walnut into which she will begin to lay eggs.
 
The sperm that was stored earlier and kept dormant over winter is now used to fertilize the eggs being laid. The storage of sperm inside the female queen allows her to lay a considerable number of fertilized eggs without the need for repeated mating with a male wasp. For this reason a single female queen is capable of building an entire colony from only herself. The queen initially raises the first several sets of wasp eggs until enough sterile female workers exist to maintain the offspring without her assistance. All of the eggs produced at this time are sterile female workers who will begin to construct a more elaborate nest around their queen as they grow in number.
 
By this time the nest size has expanded considerably and now numbers between several hundred and several thousand wasps. Towards the end of the summer, the queen begins to run out of stored sperm to fertilize more eggs. These eggs develop into fertile males and fertile female queens. The male drones then fly out of the nest and find a mate thus perpetuating the wasp reproductive cycle. In most species of social wasp the young queens mate in the vicinity of their home nest and do not travel like their male counterparts do. The young queens will then leave the colony to hibernate for the winter once the other worker wasps and founder queen have started to die off. After successfully mating with a young queen, the male drones die off as well. Generally, young queens and drones from the same nest do not mate with each other; this ensures more genetic variation within wasp populations, especially considering that all members of the colony are theoretically the direct genetic descendants of the founder queen and a single male drone. In practice, however, colonies can sometimes consist of the offspring of several male drones. Wasp queens generally (but not always) create new nests each year, probably because the weak construction of most nests render them uninhabitable after the winter.
 
Unlike honey bee queens, wasp queens typically live for only one year. Also queen wasps do not organize their colony or have any raised status and hierarchical power within the social structure. They are more simply the reproductive element of the colony and the initial builder of the nest in those species which construct nests.
 
Not all social wasps have castes that are physically different in size and structure. In many polistine paper wasps and stenogastrines, for example, the castes of females are determined behaviorally, through dominance interactions, rather than having caste predetermined. All female wasps are potentially capable of becoming a colony's queen and this process is often determined by which female successfully lays eggs first and begins construction of the nest. Evidence suggests that females compete amongst each other by eating the eggs of other rival females. The queen may, in some cases, simply be the female that can eat the largest volume of eggs while ensuring that her own eggs survive (often achieved by laying the most). This process theoretically determines the strongest and most reproductively capable female and selects her as the queen. Once the first eggs have hatched, the subordinate females stop laying eggs and instead forage for the new queen and feed the young; that is, the competition largely ends, with the losers becoming workers, though if the dominant female dies, a new hierarchy may be established with a former "worker" acting as the replacement queen. Polistine nests are considerably smaller than many other social wasp nests, typically housing only around 250 wasps, compared to the several thousand common with yellowjackets, and stenogastrines have the smallest colonies of all, rarely with more than a dozen wasps in a mature colony.
 
The German wasp, or European wasp, Vespula germanica, is a wasp found in much of the Northern Hemisphere, native to Europe, northern Africa, and temperate Asia. It has been introduced and is well-established in many other places, including North America, South America (Argentina and Chile), Australia and New Zealand. German wasps are part of the family Vespidae and are sometimes mistakenly referred to as paper wasps because they build a grey paper nest—although, strictly speaking, paper wasps are part of the subfamily Polistinae. In North America, they are also known as yellowjackets.
 
The German wasp is about 13mm (0.5 inch) long, and has typical wasp colours of black and yellow. It is very similar to the common wasp (Vespula vulgaris), but seen head on, its face has three tiny black dots. German wasps also have black dots on their abdomen, while the common wasp's analogous markings are fused with the black rings above them, forming a different pattern
The nest is made from chewed plant fibres, mixed with saliva. They are generally found close to or in the ground, rather than higher up on bushes and trees like hornets. It has open cells and a petiole attaching the nest to the substrate. The wasps produce a chemical which repels ants, and secrete it around the base of this petiole in order to avoid ant predation.
 
A solitary female queen starts the nest, building 20–30 cells before initial egg-laying. This phase begins in spring, depending on climatic conditions. She fashions a petiole and produces a single cell at the end of it. Six further cells are then added around this to produce the characteristic hexagonal shape of the nest cells.
 
Once the larvae have hatched as workers, they take up most of the colony’s foraging, brood care and nest maintenance. A finished nest may be 20–30 cm across and contain 3,000 individuals.
 
Each wasp colony includes one queen and a number of sterile workers. Colonies usually last only one year, all but the queen dying at the onset of winter. However, in mild climates such as New Zealand, around 10% of the colonies survive the winter. New queens and males (drones) are produced towards the end of the summer, and after mating, the queen overwinters in a crack or other sheltered location.
 
This common and widespread wasp collects insects including caterpillars to feed to its larvae, and is therefore generally beneficial. The adults feed on nectar and sweet fruit, and are also attracted to human food and food waste, particularly sodas and meats.
 
The nests are subject to predation by the Honey Buzzard, which excavates them to obtain the larva. The hoverfly Volucella pellucens and some of its relatives lay their eggs in the wasp's nest, and the larva feeds on the wasp's young.
 
This species is considered a pest in most areas outside its native range, though its long residency in North America is such that it is not treated with any level of urgency there, in contrast to areas such as South America, where the introduction is more recent, and the impacts far more dramatic, prompting a greater degree of concern over control measures.
 
Along with the closely related common wasp and two species of Polistes, the German wasp is likewise considered to be a pest in New Zealand. It was probably introduced in the late 19th century, but did not appear in large numbers until around 1940. It is common in the beech forest since it is one of the two wasps that feeds on the honeydew exuded by the native beech scale insect which lives in the bark of the trees, eventually killing the tree. It has a serious effect on the forest ecology since there is less honeydew available for the native birds. In domestic situations nests have been known to become very large, sometimes taking up entire attic spaces in houses. This is put down to the comparatively mild winters experienced in New Zealand, as opposed to the wasp's usual European habitat.
 
An unusual attempt at wasp control is related from Abercairney in Scotland, where until the 1950s children were encouraged to compete in the Wasp Cup, awarded to the competitor who handed in the most queen wasps. The wasps were stuck to card and a payment of 1d was made for each; totals of forty were not uncommon.
 
The common wasp, Vespula vulgaris, is a yellowjacket wasp found in much of the Northern Hemisphere, and introduced to Australia and New Zealand. It is a eusocial vespid, which builds its grey paper nest on a structure capable of supporting it, such as a tree, or underground, often using an abandoned mammal hole as a start for the site, which is then enlarged by the workers. The foundress queen may also select a hollow tree, wall cavity, or rock crevice for a nest site.
 
Adult workers of the common wasp measure about 12–17 millimetres (0.47–0.67 in) from head to abdomen, whereas the queen is about 20 millimetres (0.79 in) long. It has aposematic colours of black and yellow and is very similar to the German wasp (or European wasp, Vespula germanica) but seen head on, its face lacks the three black dots characteristic of that species. Additionally it can be distinguished by a lack of black dots on its back (gastral terga), which are located further up and form part of the black rings on each of the abdomen's six segments. Furthermore the genal area – the part of the head to which the jaws of an insect are attached – is usually broken by black .
 
Common wasps are colloquially known as "jaspers" in South East England and more commonly the English Midlands, although it is not clear whether the etymology refers to the Latin name "vespa" or the striped abdomen, which echoes the striped mineral jasper.
 
The nest is made from chewed wood fibres, mixed with saliva. It has open cells and a cylindrical column known as a "petiole" attaching the nest to the substrate. The wasps produce a chemical which repels ants and secrete it around the base of the petiole in order to avoid ant predation. A solitary female queen starts the nest, building 20–30 cells before initial egg-laying. This phase begins in spring, depending on climatic conditions. She fashions a petiole and produces a single cell at the end of it. Six further cells are then added around this to produce the characteristic hexagonal shape of the nest cells. One egg is laid in each cell and as they hatch each larva holds itself in the vertical cells by pressing their bodies against the sides. The queen now divides her time between feeding the larvae on the juices of masticated insects and nest building.[3] Once the larva reaches full size it spins a cover over the cell, pupates and metamorphosises into an adult. When enough adult workers have emerged they take up most of the colony’s foraging, brood care and nest maintenance, and the queen, who is now fed by the workers, concentrates all her energy on reproduction. The spherical nest is built, from the top downwards, with successive combs of cells separated by petioles. The queen larvae, know as "gynes", are reared in larger cells in the lower combs.The finished nest may contain 5,000–10,000 individuals.
 
Each wasp colony includes one queen and a number of sterile workers. Colonies usually last only one year, with all but the queen dying at the onset of winter. New queens and males (drones) are produced towards the end of the summer, and after mating, the queen overwinters in a hole or other sheltered location, sometimes in buildings. Wasp nests are not reused from one year to the next, however, in the mild climate of New Zealand and Australia, a few of the colonies may survive the winter, although this is much more common with the German wasp.
This common and widespread wasp collects insects including caterpillars to feed to its larvae; the adults feed on nectar and sweet fruit. Common wasps will also attempt to invade honey bee nests to steal their honey; the bees will attempt to defend their nest by stinging the wasp to death.
 
Common wasp nests are subject to predation by the Honey Buzzard, which excavates them to obtain the larva. As the wasps have a tendency to build nests near houses, they are not necessarily defensive of their hive and can often be approached without immediate attack.
 
The hoverfly Volucella pellucens and some of its relatives lay their eggs in a wasp nest and their larvae feed on the wasps’ young and dead adults. Spiders are yet another predator of this and many other species.
 
Along with the German wasp and two species of Polistes (all invasive species), the common wasp is considered a pest species in New Zealand as it competes with endemic species for food, such as insects and honeydew.