| Hornet | |
|---|---|
| Oriental hornet, Vespa orientalis | |
| Scientific classification | |
| Kingdom: | Animalia |
| Phylum: | Arthropoda |
| Class: | Insecta |
| Order: | Hymenoptera |
| Suborder: | Apocrita |
| Family: | Vespidae |
| Subfamily: | Vespinae |
| Genus: | Vespa Linnaeus, 1758 |
| Species | |
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See text |
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Hornets are the largest eusocial wasps; some species can reach up to 5.5 cm (2.2 in) in length. The true hornets make up the genus Vespa and are distinguished from other vespines by the width of the vertex (part of the head behind the eyes), which is proportionally larger in Vespa and by the anteriorly rounded gasters (the section of the abdomen behind the wasp waist).
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In Vespa crabro, the nest is founded in spring by a fertilized female known as the queen. It generally selects sheltered places like dark hollow tree trunks. It first builds a series of cells (up to 50) out of chewed tree bark. The cells are arranged in horizontal layers named combs, each cell being vertical and closed at the top. An egg is then laid in each cell. After 5–8 days, the egg hatches, and in the next two weeks, the larva undergoes its five stages. During this time, the queen feeds it a protein-rich diet of insects. Then, the larva spins a silk cap over the cell's opening and, during the next two weeks, transforms into an adult, a process called metamorphosis. Then, the adult eats its way through the silk cap. This first generation of workers, invariably females, will now gradually undertake all the tasks that were formerly carried out by the queen (foraging, nest building, taking care of the brood, etc.) with one exception: egg-laying, which remains exclusive to the queen.
As the colony size grows, new combs are added, and an envelope is built around the cell layers until the nest is entirely covered with the exception of an entry hole. At the peak of its population, the colony can reach a size of 700 workers, which occurs in late summer.
At this time, the queen starts producing the first reproductive individuals. Fertilized eggs develop into females (called "gynes" by entomologists), and unfertilized ones develop into males (sometimes called "drones"). Adult males do not participate in nest maintenance, foraging, or caretaking of the larvae. In early to mid-autumn, they leave the nest and mate during "nuptial flights". Males die shortly after mating. The workers and queens survive at most until mid to late autumn; only the fertilized queens survive over winter.
Other temperate species (e.g. the Yellow hornet, V. simillima, or the Oriental hornet, V. orientalis) have similar cycles. In the case of tropical species (e.g., V. tropica), life histories may well differ, and in species with both tropical and temperate distributions (such as the Asian giant hornet, Vespa mandarinia), it is conceivable that the cycle depends on latitude.
Hornets have stings used to kill prey and defend nests. Hornet stings are more painful to humans than typical wasp stings because hornet venom contains a large amount (5%) of acetylcholine.[1] See Schmidt Sting Pain Index.[2] Individual hornets can sting multiple times; unlike typical bees, hornets and wasps do not die after stinging because their stingers are not barbed and are not pulled out of their bodies.
The toxicity of hornet stings varies according to hornet species; some deliver just a typical insect sting, while others are among the most venomous known insects.[3] Single hornet stings are not in themselves fatal, except sometimes to allergic victims.[3] Multiple stings by non-European hornets may be fatal because of highly toxic species-specific components of their venom.[4] The stings of the Asian giant hornet (Vespa mandarinia japonica) are the most venomous known.[3]
People who are allergic to wasp venom are also allergic to hornet stings. Allergic reactions are commonly treated with epinephrine (adrenaline) injection using a device such as an EpiPen, with prompt followup treatment in a hospital. In severe cases, allergic individuals may go into anaphylactic shock and die unless treated promptly.[5]
Hornets, like many social wasps, can mobilize the entire nest to sting in defense, which is highly dangerous to animals, including humans. The hornet attack pheromone is released in case of threat to the nest, and to mark prey, such as bees.[6] Three biologically active chemicals: 2-pentanol, 3-methyl-1-butanol, and 1-methylbutyl 3-methylbutanoate, have been identified. In field tests, 2-pentanol alone triggered mild alarm and defensive behavior, but adding the other two compounds much exacerbated aggressiveness in a synergistic effect[6].
If a hornet is killed near a nest it may release pheromone which can cause the entire nest to attack. Materials that come in contact with pheromone, such as clothes, skin, and dead prey or hornets, can also trigger an attack, as can certain food flavorings, such as banana and apple flavorings, and fragrances which contain C5 alcohols and C10 esters.[6]
Hornets prey on bees and many insect pests. Hornet colonies die out every winter.
While taxonomically well-defined, there may be some ambiguity about the differences between hornets and other wasps of the family Vespidae, specifically the yellow jackets, which are members of the same subfamily. Yellow jackets are generally smaller than hornets and are bright yellow and black, whereas hornets may often be black and white—see wasp and bee characteristics.
Another major difference between yellow jackets and hornets is each of their food choices and aggression towards humans. In autumn, yellow jackets may be attracted to human foods and food wastes, increasing potentially aggressive contact between yellow jackets and humans. Hornets, on the other hand, tend to stick to live insects.
Some other large wasps are sometimes referred to as hornets, most notably the bald-faced hornet (Dolichovespula maculata) found in North America. It is set apart by its black and ivory coloration. The name "hornet" is used for this and related species primarily because of their habit of making aerial nests (similar to the true hornets) rather than subterranean nests. Another example is the Australian hornet (Abispa ephippium), which is actually a species of potter wasp.