The Asian hornet or yellow-legged hornet (Vespa velutina Lepeletier, 1836) is a hymenoptera belonging to the Vespidae family.
From a systematic point of view it belongs to:
V. velutina species.
The terms are synonymous:
– Vespa velutina Lepeletier, 1836;
– Vespa immaculata Morawitz, 1889;
– Vespa auraria Smith, 1852;
– Vespa fruhstorferi Stadelmann, 18941.
Within this species, some subspecies are also recognized but the taxonomic verification is still under review.
Geographic Distribution and Habitat –
The Asian hornet is a hymenopteran native to Southeast Asia, widely distributed in India, Indochina, China and Java.
Its introduction in Europe was found for the first time in 2005 in France where it was accidentally introduced in the southern part of the country. It later spread to Spain, Portugal, Belgium and Italy.
The Vespa velutina is slightly smaller than the European hornet (Vespa crabro Linnaeus, 1758).
Queens are around 30mm long and males around 24mm.
The workers measure about 20 mm in length.
The species is recognized by the yellow legs of the legs.
The chest is a velvety brown or black color and the abdomen is brown. Each abdominal segment has a narrow posterior yellow border, with the exception of the fourth segment, which is orange.
The head is black and the face is yellow.
The different regional subspecies vary sufficiently in color to cause difficulties in classification, and several subspecies have been variously identified and ultimately rejected; while there is a history of subspecies recognition within many Vespa species, including V. velutina, the most recent taxonomic revision of the genus treats all subspecies names of the genus Vespa as synonyms, effectively relegating them to nothing more than informal names for the regional color of the shapes.
The form causing concern for its invasiveness in Europe has been referred to as V. v. nigrithorax, even if, we repeat, this name no longer has any taxonomic value.
This shape is on average 30 mm long and is recognizable by the dark body and the yellow line that cuts its abdomen, inside which there is a black triangle.
Finally, as regards the recognition of this species, given that the queen in rare cases can approach the size of 35 mm, sometimes the presence of Velutina in Europe is erroneously reported as Vespa mandarinia, much more aggressive, which however does not seem to find documented findings. The confusion is increased by the very definition of Asian hornet, which refers to the area of origin in common with V. mandarinia.
Attitude and Life Cycle –
The Vespa velutina, like other hornets, builds nests that can host colonies of several thousand individuals.
The females of the colony are armed with formidable stingers with which they defend their nests and kill their prey.
The nesting period is long, and a colony commonly begins by building a nest in a low shrub, then abandoning it after a few months and quickly building a new one high up in a tree, possibly as a pest measure. The next generation of young queens disperse in the late fall to hibernate during the winter.
The construction of the first nest takes place by the founding queen of the colony who creates an improvised nest, called an “embryonic nest”. This nest is no bigger than a tennis ball. If the provisional nest situation is suitable, it will serve as the basis for the construction of the colony’s final nest. If not, the first workers will build a new one, which is often on top of a tree (often more than 15m high) but also (less often) can be hung on the facade of a building (gutters, windows … .) and also in bushes, hedges, ferns or in hollows of the ground. The final nest (which is not a hive) is called a “secondary nest”.
The nests are made of chewed wood fibers, and can reach a meter in height and 80 cm in diameter. The largest nests are maintained by thousands of individuals. Generally these nests are spherical or oval in shape, and have a lateral exit hole, unlike those of the hornet (Vespa crabro Linnaeus, 1758), which have their exit in the lower part. Each large nest is home to around 2,000 wasps, and at the end of the season it produces up to several hundred fertile females (potential queens). Of these, those that survive the winter will be the founding queens who will create a series of new colonies the following spring. The workers and the males die before the end of autumn; fertile females diapause in sheltered places, so they will leave their nests empty and will not use them the following year.
It should be noted that the nests built in the canopy of tall trees are difficult to see and find during the spring and summer, hidden by the foliage.
From observation, it is concluded that this species prefers oaks, poplars and acacias but avoids conifers. However, nests can also be found in the most unlikely places.
During the winter, any small, well-isolated area (natural or man-made) can be inspected for the presence of fertile hibernating queens. Garages, sheds, lower decks, cornices, cornices, even holes, uninhabited houses, in the walls or in the floor.
To identify the nest, it is emphasized that it is spherical in shape and in the last stages of construction, which is the end of summer and autumn, it can measure between 70 and 90 cm. height and 40 and 70 cm. diameter.
Ecological Role –
The Asian hornet, like the common vespids widespread in Europe, has a sting and has a fairly aggressive behavior towards humans. According to entomologists, its dangerousness, for humans and mammals in general, and also its aggressiveness should be compared to that of other European wasps.
For this reason the Velutina cannot be considered more dangerous than the crabro wasp which, by virtue of its greater size, has, if anything, more poison. In fact, it is often the confusion with the Vespa mandarinia that creates the greatest rumors in this sense.
On the other hand, its danger to bees, its favorite food, is greater, especially as regards European species. Although a very skilled predator of bees even in its territory of origin, it is in Europe that this hymenoptera manages to seriously undermine the existence of apiary communities. The apiary species of Southeast Asia have in fact adopted valid behaviors to combat this predator of theirs and not yet known to European bees.
Among other things, the adult Vespa velutina does not eat insects. However, it hunts bees, various insects and other invertebrates, and this is because they capture them to take them to the nest and feed their larvae.
To feed its larvae, Vespa velutina captures many types of insects and other invertebrates (bees, wasps, flies, spiders, caterpillars, ants, butterflies and aphids), but bees make up 84% of its diet (especially for feed their own larvae).
According to some researches, it is estimated that in urban and industrial areas bees represent up to 65% of the prey captured; in agricultural and forest areas the percentage is reduced to 33%. This last factor could be related to the greater biodiversity of agricultural areas.
To catch bees, the wasp hovers at the entrance to the hives. Its larger size allows it to catch a flying bee and kill it, to preserve only the chest, which it will take to the colony to feed its larvae.
The adult wasp instead feeds on flower nectar and other sweet substances, such as ripe fruits (apples, plums, grapes, etc.), just like native European wasps, but in larger quantities, and can damage orchards. It is not uncommon for them to frequent places such as vineyards or fruit plantations.
In Europe, the Asian hornet (Vespa velutina) has predators such as the shrike (Lanius collurio), the bee-eater (Pernis apivorus) and the bee-eater (Merops apiaster). Birds such as the magpie, and even chickens, may be predators of the Asian hornet. Occasionally woodpeckers (Picus spp.) Have been seen piercing the nests to feed on the colony’s larvae or adults. The role of predators as a biological control measure is very important in the destruction of the first nests.
Among other things, the Asian bees, which have lived with the Vespa velutina for a long time, do not suffer the same predation as the European ones. This is because some Asian bees have learned to defend themselves using a technique that consists of creating a swarm around the wasp to cause an increase in body temperature. In this way they manage to kill them, because the bees are able to withstand more than 45 degrees; wasps, on the other hand, do not tolerate that temperature.
Although the main method of defense is the one mentioned above, other systems have also been observed consisting of using low frequency sounds or causing them to suffocate.
European bees introduced to the Asian continent have also learned to defend themselves, albeit much less efficiently than Asian bees.
European bees are starting to develop the same defense strategy as their Asian counterparts. Its defense in the hive consists in covering an attacking wasp causing it to die from hypoxia after a few minutes.
The biocontrol of the Vespa velutina has been attempted with various means, such as the use of carnivorous plants, however the first thing to do when you suspect the presence of this wasp is to notify the local phytosanitary services and activate some measures. control such as the destruction, above all, of the first nest (to be done with specialized personnel) and to place traps made even at home with open bottles above inside which to place sugary liquids, beer and other substances that tend to decompose producing ammonia products that attract the insect.
In addition, the increase in corporate biodiversity, the cleaning of some places, can help rearrange some biocoenoses in favor of bees.
Finally, as far as humans are concerned, the Asian hornet, like the European hornet, can represent a danger with its venom. According to data collected in Europe, the Vespa velutina does not represent any more danger than its European counterpart, but due to its size, the stings cause more pain, as it is able to inoculate a greater amount of poison.
However, they both prefer to escape before the attack, except when it comes to defending the nest. If the nest is shaken or damaged, the wasps first come out and perch on it to observe what happens. If the nest is disturbed again, one or more wasps fight the intruder by biting it quickly, even through clothes, and retreat, landing on the nest again. Their guideline is to defend the nest at all costs, to the point that if it is set on fire, the wasps risk their lives defending it and may even die.
It should be noted that there are no records of increases in stings in the areas where the Vespa velutina has established itself. Known cases of attack have almost always occurred near the nest. The pain caused by the sting is intense and sharp, as if caused by a large pin, and then develops into a tingling that resembles a burn. The swelling can be relieved by applying ice and vinegar, and the discomfort lasts for several days to a week, which may require pain relievers and anti-inflammatories. The danger to human life occurs in the case of multiple stings, a single sting in the mucous membrane or in people suffering from allergy to hymenoptera venom.
– Wikipedia, the free encyclopedia.
– Russo G., 1976. Agricultural Entomology. Special Part. Liguori Editore, Naples.
– Pollini A., 2002. Manual of applied entomology. Edagricole, Bologna.
– Tremblay E., 1997. Applied entomology. Liguori Editore, Naples.