The European hornet (Vespa crabro) is the largest eusocial wasp in Europe and the largest vespine in North America. It is actually the only true hornet found in North America. V. crabro is usually regarded as a pest by those humans who come into contact with it. Vespines, like V. crabro, are known for making nests out of surrounding plant materials and other fibers to create intricate paper nests. Unlike most other vespines, reproductive suppression involves worker policing instead of queen pheromone control as was previously thought.
This species stings in response to being stepped on or grabbed, but generally avoids conflict. It is also defensive of its hive and can be aggressive around food sources. European hornets are carnivorous and hunt large insects such as beetles, wasps, large moths, dragonflies and mantises. However, mutual predation between medium-sized hornets and robberfly (Asilidae) is often reported. Care should be taken when they are encountered in these circumstances, as they may sting without warning. The pain from the sting may persist for several days with attendant swelling. Victims may wish to seek medical attention in case of an allergic reaction.
Video European hornet
Taxonomy
The European hornet is a true hornet (genus Vespa), a group characterized by eusocial species. The genus is in the subfamily Vespinae, which is known for chewing up their food to feed it to their young as well as chewing up paper-like materials to make their nests. According to a recent phylogenetic study, its closest relative is Vespa dybowski.
Subspecies
There are multiple subspecies of European hornet, mostly distinguished by geographic color forms:
- V. c. altaica Pérez, 1910
- V. c. borealis Radoszkowski, 1863
- V. c. caspica Pérez, 1910
- V. c. chinensis Birula, 1925
- V. c. crabroniformis Smith, 1852
- V. c. crabro Linnaeus, 1758
- V. c. flavofasciata Cameron, 1903
- V. c. germana Christ, 1791
- V. c. oberthuri du Buysson, 1902
- V. c. vexator Harris, 1776, found in southern counties of England, and continental Europe: This subspecies can be distinguished from the common European hornet by its yellow head.
Maps European hornet
Description
The eyes of V. crabro are deeply indented and shaped like a "C". Its wings are reddish-orange, while the petiolate abdomen is striped with brown and yellow. It has hair on the thorax and abdomen, although the European hornet is not as hairy as most bees. Typical mass size for the European Hornet is 477.5+/-59.9 mg. Due to this coloration and abdomen pattern, V. crabro is often mistaken for the Asian giant hornet. In size, the European hornet, at 25-35 mm long, is larger than the common wasp, but smaller than the Asian giant hornet. Females are typically larger than males in both size and mass. However, male abdomens have seven segments, whereas female abdomens have six. Only females possess an ovipositor (modified to form a stinger), and males cannot sting. The antennae of males are slightly longer, with 13 segments compared to 12 segments in females.
Nests
Individuals typically live in paper nests, which consist of a pedicle (a paper comb on the inside), an envelope, and a single entry hole on the outside. Materials such as twigs, branches, and other available plant resources are broken up, chewed, and shaped into a nest by the workers. These pieces are not uniform in shape, but are glued together very closely. Because social wasps generally prefer to build nests in the dark, envelopes are commonly found surrounding the nests to make them dark if the colony could not locate a dark crevice in which to build.
Construction
The nest is composed of a paper-pulp mixture created by female workers chewing up dead bark, trees, or plant matter from nearby surroundings and mixing it with their saliva. To build the actual comb, saliva is used as a cement to piece together organic and inorganic materials that are readily available to the colony. This cement not only holds together the comb, but also protects the comb from being damaged by water. It provides a protective barrier to help protect the colony from wind or other harsh weather conditions. Available resources, location, and amount of mastication affect the final nest's appearance, so much variation is seen among the nests of V. crabro.
Physical and chemical composition
Minerals such as titanium, iron, and zirconium are commonly found in the soil and they, too, become part of the comb walls. The average dry weight of the nest is about 80.87 g. Cells in the paper comb are typically 4 to 5 mm long and 8 to 9 mm in diameter. Elemental composition of nests in northern Turkey included oxygen, carbon, and nitrogen as the main elements, while elements found in trace amounts were silicon, calcium, iron, and potassium, but no aluminum, magnesium, or sodium were detected, providing further evidence that European hornets use the surrounding soil as a resource in building their nests. The ratio of fibrous material to actual saliva affects the nest's ability to absorb water, thus how well the inside of the nest stays dry. In nests studied in Turkey, fiber content was 23% while 77% was hornet saliva. This combination resulted in optimal water absorption capacity.
Distribution
As the name, European hornet, implies, V. crabro originated in Eurasia. Nests historically ranged from Japan to the United Kingdom. However, Saussure reported that V. crabro was introduced to North America in the mid-19th century, where it is now well-established. In 2010, they were found as far south as Guatemala. The few nests found in Guatemala were thought to be recent, accidental, introductions, since these were the first documented occurrences.
Life cycle
V. crabro prefers to build nests in dark places, usually hollow tree trunks. After the site has been chosen, the queen lays eggs in the combs inside the nest. The workers dispose of any eggs that are not laid by their queen; this behavior is called worker policing. Based on laboratory data, the rate of egg-laying is roughly 2.31 eggs per day. However, in this same nest, cell construction rate was only 1.63 cells per day.
V. crabro colonies seasonally change strategies of obtaining food for both the larvae and adults. In April, when the queen normally lays her eggs, the workers actively go out and forage. Later, typically around the fall season, the foraging workers switch to scavengers. Instead of putting forth the effort to catch food sources, the workers try to take what is more easily available. For example, European hornets have been seen hovering around garbage cans and picnic areas in the fall.
Worker policing
Very few workers lay eggs in healthy V. crabro colonies. While only queens mate and produce fertilized female eggs, workers are capable of laying haploid male eggs. Workers are generally more closely related to male offspring of other workers than to male offspring of the queen. Workers would have reproductive benefits from laying male eggs, but do not do so. This was originally thought to be caused by pheromone control by the queen. However, new evidence has shown that this is not the case. Workers enforce sterility on one another in a strategy known as worker policing. Workers either physically destroy worker-laid eggs or by discriminate against those workers that attempt to lay eggs. Ensuring only the queen reproduces likely benefits the organization and productivity of the colony as a whole by reducing conflicts.
Alarm behavior
Social hymenopteran species typically communicate with each other through behaviors or pheromones. In the European hornet, a typical alarm dance is performed outside of the nest and consists of consistent buzzing, darting in and out of the nest, and attacking or approaching the target of the alarm pheromone. The alarm pheromone is stored in, and secreted from, internal venom sacs. 2-methyl-3-butene-2-ol is the main pheromone component which causes V. crabro to express this defensive behavior. Other pentenols and pentanols are contained within these venomous sacs, but their primary purpose is likely not to warn fellow hornets that there is danger nearby, because these chemicals do not induce alarm behavior.
Kleptoparasitsm
European hornets have been observed to steal prey from spiders, which can be classified as an example of kleptoparasitism. This behavior was first documented in 2011 against the yellow garden spider, Argiope aurantia. Hornets were observed to fly into the spider's web and appear entangled. However, the hornet cut free prey that had been caught by the spider's web. The spider did not attack or interfere with V. crabro as the wasp was stealing its prey. This behavior follows the pattern of most vespines changing their foraging techniques from hunting for food to scavenging, especially once the fall season begins.
In addition, V. crabro has been observed attacking Polistes nimpha nests.
Relationship with humans
Endangered species and legal protection
Unwarranted fear of V. crabro has often led to the destruction of nests. This has led to the decline of the species, which is often locally threatened or even endangered. European hornets benefit from legal protection in some countries, notably Germany, where it has been illegal to kill a European hornet or nest since January 1, 1987, with a fine up to EUR50,000.
Problems associated
European hornets are carnivores and eat many species of insects. Many of these insects are considered to be garden pests, which indicates that the hornet provides a benefit to the average garden or farm. However, they are also known to "hawk" in midair for honeybees near their hive, which they then take down and consume. They can even eradicate honeybees inside their hives, if the bee colony is too weak for other reasons to protect itself. This, of course, results in fewer honeybees for pollination. European hornets also tend to girdle branches, which results in dead branches.
Stings: case study
Most cases of stings from V. crabro do not require medical attention, but can rarely be serious. A documented case requiring treatment displayed symptoms including tingling at the site of the sting, as well as headaches and shortness of breath. In the hospital, the victim was found to have a fast, irregular heartbeat with a blood pressure of 111/63. A subsequent ECG demonstrated atrial fibrillation with a rapid ventricular response. V. crabro venom contains neurotransmitters such as dopamine, serotonin, and noradrenalineneurotoxin apamin, as well as enzymes phospholipase A and hyaluronidase, the compound histamine, and proteins melittin and bradykinin. These compounds have been shown to cause tachycardia episodes in smaller animals. The mechanism of the described attack is still undetermined, but it is possible the victim was abnormally susceptible to vespine stings. Currently, the two most effective treatments for reactions are electrical cardioversion or propafenone. The victim in this case study was given an oral dose of propafenone (150 mg) and his atrial fibrillation resolved.
See also
- Hornet stings
- Vespidae
Notes
External links
- European hornet protection site
- European Hornet - Penn State Entomology Department Fact Sheet
- "The European hornets and oak sap"
Source of article : Wikipedia
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