Hornets are the largest eusocial wasps, that reach up to 45 millimetres (1.8 inches) 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).
The genus Vespa
comprises about 20 species
, most of which are native to tropical and desert southern Asia
, but there is a species found across temperate Eurasia
, the European hornet
), and another, the Oriental hornet
), that extends via southern and central Asia to the Arabian peninsula
, up to northern and eastern Africa
and the Mediterranean basin
(including southern Italy
). The European hornet V. crabro
, was accidentally introduced to North America
in 1840 and is now present in many eastern regions; it is the only true hornet in North America. As of 2003, its geographical range extends from the Northeastern United States
west to the Dakotas
, and south to Louisiana
. Another occurs in temperate eastern Asia, the Yellow hornet
), and some tropical species also range as far north as China
, or Japan
. The Asian giant hornet
) is a native of temperate and tropical Asia.
In Vespa crabro, the nest is founded in spring by a fertilized female, known as the queen. She generally selects sheltered places like dark hollow tree trunks. She builds a first 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 it 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 her 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. This occurs in late summer.
At this time the queen starts producing the first reproductive individuals. Fertilized eggs develop into females (called "gynes" by entomologists), unfertilized ones 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.
The workers accomplish a variety of tasks during the colony's lifetime. These include:
- Foraging. Workers feed mainly on carbohydrate-rich fluids such as tree sap. They also hunt other insects, primarily flies but also other species including smaller wasps and bees; they have been known to attack dragonflies. After subduing the prey, the hornet may discard all nutrient-poor parts such as the wings, legs, head, and/or abdomen. This leaves only the thorax with the protein-rich flight muscles, which constitutes the main food of the larvae. On hot days, workers will bring water to the nest and deposit it on the envelope, thus cooling the interior.
- Expanding and rearranging the nest. This includes building new combs and new cells.
- Feeding the larvae. On returning back to the nest, masticated prey flesh is fed to the larvae, which have higher protein needs (for growth) than the workers, since they no longer grow. The larvae, in turn, produce a nutrient fluid, rich in amino acids, which is consumed by the adults, especially the queen.
A hornet's sting is painful to humans, but the sting toxicity varies greatly by hornet species. Some deliver just a typical insect sting, while others are among the most venomous known insects. Allergic reactions, fatal in severe cases, can occur—an individual suffering from anaphylactic shock
may die unless treated immediately via epinephrine
("adrenaline") injection using a device such as an EpiPen
, with prompt followup treatment in a hospital.European hornet sting
- in itself is not fatal except sometimes to allergic victims.
- multiple stings (several hundred) may be fatal due to the amount of venom (similar to wasps and bees).
- is similar to a wasp's.
- is less toxic than a bee sting.Non-European hornet sting
- in itself is not fatal except sometimes to allergic victims.
- multiple stings (a nest full) can be fatal due to highly toxic species-specific additions in the venom.
- is more toxic than a wasp's or bee's sting
- from the Asian giant hornet (Vespa mandarinia japonica) is the most venomous known (per sting).All hornet stings
- are an allergen for people with an allergy to wasp venom.
- those allergic to wasp venom are not necessarily allergic to bee venom as they contain different chemicals.
- contain less volume of venom than a bee sting.
- are primarily for killing insect prey.
- are more painful than a typical wasp's due to a large amount (5%) of acetylcholine. See Schmidt Sting Pain Index.
As in all stinging wasps, hornets can sting multiple times—they do not die after stinging a human, as is typical for a worker honey bee, as the sting is not barbed (the honey bee stinger has evolved for defending the nest against vertebrates/mammals). They can also bite and sting at the same time.
Hornets, like many social wasps, can mobilize the entire nest to sting in defense: this is highly dangerous to humans. The hornet alarm pheromone is used to raise alarm of nest attack, and to identify prey, for example bees . It is not advisable to kill a hornet anywhere near a nest, as the distress signal can trigger the entire nest to attack. Materials that come in contact with pheromone, such as clothes, skin, dead prey or hornets, must be removed from the vicinity of the hornets nest. Perfumes, and other volatile chemicals can be falsely identified as pheromone by the hornets and trigger attack.
Actions to avoid
- Disturbing a nest (including vibrations and loud noises)
- Being within a few meters of a nest
- Disturbing or killing a hornet within a few meters of a nest
- Blocking the path of a hornet
- Breathing on the nest or hornet
- Rapid air movements
Hornets and yellowjackets prey on many insects that are considered to be pests, so are actually beneficial. They do also prey on bees, but unlike honey bees, hornet and yellowjacket colonies die out every winter.
Hornets and other Vespidae
While taxonomically well-defined, there may be some ambiguity about the differences between hornets and other wasps of the family Vespidae, specifically the yellowjackets, which are members of the same subfamily. Yellowjackets are generally smaller than hornets and are bright yellow and black, whereas hornets may be darker in color - see wasp and bee characteristics.
Another major difference between yellowjackets and hornets are their food choices and aggression towards humans. In the fall, yellowjackets may be attracted to human foods and food wastes, increasing potentially aggressive contact between yellowjackets 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.
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