Hornet
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? Hornet |
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 European hornet,
Vespa
crabro
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Hornets are large eusocial wasps. The true hornets make up the genus Vespa, and are distinguished from other vespids 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).
Geographical distribution
The genus Vespa comprises about 20 species, most of which are native to tropical Asia, but there is a species found across temperate Eurasia from Britain to Japan (V. crabro), another (V. orientalis) that extends via southern and central Asia to the Arabic peninsula, up to northern and eastern Africa and the Mediterranean basin (including southern Italy and Sicily). Another occurs in temperate eastern Asia (V. simillima), and some tropical species also range as far north as China, Siberia or Japan. The European hornet V. crabro has been accidentally introduced to North America and is present in many eastern states.
Life cycle of the European hornet (a temperate species)
Other temperate species (e.g. the yellow hornet V. simillima or the Oriental hornet V. orientalis) may 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. Such information could not be found on the web.
In Vespa crabro, the nest is founded in spring by a fertilized female, known as the queen. She generally selects sheltered places like 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 done exclusively by 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 (called drones). Adult sexuals do not participate in nest maintenance, foraging, or caretaking of the larvae. In early to mid-autumn they leave the nest and mate during mating flights. The drones die shortly after the flights. The workers and queens survive at most until mid to late autumn; only the fertilized queens overwinter.
Hornets often live together with Velleius dilatatus
Worker tasks
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 (and queen ?). 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 and queen. On returning back to the nest, masticated prey flesh is fed to the larvae and queen, which have higher protein needs (respectively for growth and egg-laying) than the workers, since they no longer grow.
Relationships with humans
Stings
Hornets are often (although wrongly) thought to be very aggressive and dangerous, and are much feared by some people. Hornets can actually be seen to slowly crawl backwards and eventually flee, rather than attacking, when approaching them. This can make it hard to remove hornets from indoors, if they happen to come in through an open window or door. Some folk beliefs have it that three stings from the European hornet can kill an adult human, and that seven can kill a horse. While impressive due to their size, European hornets are in fact much less aggressive than some of their smaller relatives (notably the yellowjackets Vespula germanica and Vespula vulgaris), and their sting isn't more dangerous. Unwarranted fear has often led to the destruction of nests, and the species is locally threatened. It benefits from legal protection in some countries, notably Germany.
Hornets are not harmless, however. They have a painful sting and can cause anaphylactic shock to persons with an allergy to wasp venom, a condition which can be fatal. While not aggressive when encountered far from the nest, workers will vigorously defend the nest if provoked.
False hornets
Some other large wasps are usually referred to as hornets, though they are not true hornets in the sense above. These include several yellowjackets, most notable the bald-faced hornet (Vespula maculata) found in North America, which is set apart by its black and ivory coloration. Another example is the Australian hornet (Abispa ephippium), which is actually a species of potter wasp.