Vespa crabro

Vespa crabro

The hornet (Vespa crabro Linnaeus, 1761) is a large hymenoptera of the Vespidae family.

Systematics –
From a systematic point of view, it belongs to the Eukaryota Domain, Animalia Kingdom, Subgenus Eumetazoa, Bilateria Branch, Phylum Arthropoda, Subphylum Tracheata, Superclass Hexapoda, Class Insecta, Subclass Pterygota, Cohort Endopterygota, Superorder Oligoneoptera, Hymenopteroid Section, Section Hymenoptera, Suborder Apex, Section Aculeata, Superfamiglia Vespoidea, Family Vespidae, Subfamily Vespinae and therefore to the Genus Vespa and to the Specie V. crabro.
The following subspecies have been described within this species:
– Vespa crabro crabro Linnaeus, 1758 .;
– Vespa crabro vexator Harris, 1776 .;
– Vespa crabro germana Christ, 1791 .;
– Vespa crabro crabroniformis Smith, 1852 .;
– Vespa crabro oberthuri Buysson, 1902 .;
– Vespa crabro flavofasciata Cameron, 1903 .;
– Vespa crabro altaica Pérez, 1910 .;
– Vespa crabro caspica Pérez, 1910 .;
– Vespa crabro birulai Bequaert, 1931.

Geographical Distribution and Habitat –
The bumblebee is an insect widespread in Italy and central Europe with the German subspecies. However, the coexistence in Lombardy of variants with tergites of a lighter yellow and others of a yellow turning to fawn is undeniable, also in the southern regions, congener orientalis L. is also present. These two species are easily distinguishable, because V. orientalis it has red mandibles (and not yellow like crabro), the coloration of the chest and abdomen is lighter than crabro and the wings have purple shades.

Morphology –
The Vespa crabro is the largest social wasp in Europe, where it is recognized for having a massive yellow, black and rust colored body, almost hairless.
The legs are strong and measure from 2.5 to 3.5 cm; the sting is smooth and moderately aggressive (less than the Vespas).
The queen normally reaches 35 mm in length, and in some rare cases even 50 mm, while males and workers measure from 20 to 25 mm. The bumblebees live in nests outside in the shape of a sphere, built with wood mixed with their saliva. The colonies consist of about 100-300 specimens.

Attitude and biological cycle –
The biological cycle of the Vespa crabro begins in the spring when a founder wakes up from hibernation, starting to build small cells in a sheltered and difficult to locate place. Thus she begins to lay eggs which, until they develop, she will take care of. At this stage we talk about a primary nest and it represents the optimal moment in the agricultural / beekeeping sector (considering the obvious ecological considerations) to try to capture the future queen with special baits.
The nest, in the initial phase, looks like an empty hemisphere facing downwards and a few centimeters in diameter; within this reside the first cells, which are hexagonal and adjacent structures facing downwards, each containing a form of development: eggs, which after about 5-8 days become larvae.
The nest is made of a solid vegetable fiber that is obtained by mixing with the saliva the wood fibers of the young branches of various trees with soft bark, until obtaining a mouldable paste, which, once hardened, will be solid and papery .
For this reason the nests of the Vespa crabro have a paper consistency, although they are relatively waterproof and very resistant.
A medium-sized hornet’s nest can also contain 5,000 cells. In the colonies we distinguish: the queen (the only one that reproduces), the workers, the males and the fertilizable females.
The larvae for growing up take a period of 2 or 3 weeks progressively occupying the volume of their cell; these are fed with other insects, mainly winged muscles, hunted and shredded by the queen.
Subsequently the mature larvae enter the pupal phase, creating a sericeous cork to close inside the cells before turning, over another couple of weeks, into adult wasps.
These will be workers, sterile females, dedicated to the care of the colony. The first handful of workers, raised by the queen alone, remains small. In fact, before their emergence, it is the only queen that nourishes and expands the nest.
After the birth of the first worker wasps, the future queen gradually abandoned her initial duties and dedicated herself to laying eggs only. The queen, fed by the workers, going from cell to cell, lays eggs and checks that the larvae are all her daughters, otherwise she kills them.
The workers’ task is to: nurses, groomers, foragers, guardians, builders.
The maximum size of the colony will be towards the month of September, when also the population of workers is at its maximum. The activity of the colony is very hectic, because a consistent brood needs to be fed.
From the moment of the flicker of the first workers and from the first floor of cells, during the summer period, the colony grows more and more.
At this point, the founder, fully known as the queen, undergoes an increase in abdominal volume in response to the need to lay an ever increasing number of eggs. The workers of a mature nest in August can be of the order of hundreds.
Arrived in the period of late summer – early autumn, the queen temporarily stops laying her eggs to leave the next room the necessary space to grow. The last nest of the nest, however, is particular; in fact it will not give life to other workers but to larvae of male haploid wasps, born from unfertilized eggs, and to female wasps that will develop into new future foundresses cause the greater supply of food by the numerous workers and the decrease of dominant pheromones produced by the original queen.
Arriving at the last brood, in the period of September, the nest’s decline begins. The new queens and the males, now very numerous in spite of the workers, close to the winter start the period of mating. Each fertile female copulates with a male preferably of another colony, after which it begins to accumulate body fat through sugary liquids to prepare for the cold season. If all goes well, the fertilized females will be the queens of the following year.
In the same period the old queen, having reached the end of her procreative capacity, moves away from her kingdom and dies of old age, around September-October. After it, progressively, the workers also die and the colony quickly goes to extinction due to the missed generation exchange.
At the end of the season the males and the last brood of immature wasps (larvae of males or late females) can survive until the arrival of winter, a period which in any case they cannot overcome.
Thus, due to the lack of workers’ labor, the last larvae perish by starvation, no longer treated. This is the main cause, together with the remains of decomposing food, of the strong smell of rotten and ammonia characteristic of mature colonies, which can be felt by opening a developed nest.
The only wasps that survive in the winter are the founders who were born shortly after the males and destined to go into a sort of hibernation, from which they wake up the following spring, to try to found new colonies.
After the colony’s extinction, the paper envelope of the nest and the abandoned cells will remain, which are often looted by ants or used as a winter shelter by other insects such as hunts, ladybugs or any other insect that seeks refuge during the wintering season. Not infrequently, some fertilized females can spend the winter on the nest, together with the other host animals.
The bumblebees, as for many other types of wasps, can cause considerable damage to fruit crops, such as pears, apples, plums and grapes. A hornet colony can irreparably compromise the entire production of an apple tree in a short time, often eroding only the more mature part of the fruit and then moving on to attaching another.
The European hornets are omnivorous and as such they eat several other species of insects many of which are considered pests and therefore in this sense they bring a benefit to gardens and crops. In any case, they are harmful to the extent that they also feed on domestic bees (which they try to bring alive in the nest to feed them to the larvae), compromising the reproduction of the species, damage to the beehives, the production of honey and above all the pollination of flowers.

Ecological Role –
The Vespa crabro which, as mentioned, is the biggest European Vespide.
In the common language with the term bumblebee, the firewood bee (Xylocopa violacea) and the land bumblebee (Bombus terrestris) are often wrongly identified.
The hornet is a predominantly carnivorous insect, predator of other insects including several other species of wasps and bees. However, it does not disdain the pulp of the fruit and the sugary nectars and this helps to explain its unwelcome spread in agricultural areas.
Despite being a predominantly daytime insect, it also performs partially nocturnal activity if attracted by artificial lights which it has learned to be equally appreciated by various of its preys, and it can be found active even in late autumn. this insect, with respect to humans, tends to be indifferent and tries to escape with rapid escape or concealment from attempts to kill it, however these insects can become very aggressive if cornered or, as we have said, near the nest.
The females of this insect are equipped with a sting, whose bites (consequent to a defensive reaction of the animal) can be very painful for humans and, in addition, release pheromones that inform of the attack in progress any other hornets in the area, sometimes causing the intervention in groups. As in the case of the other wasps and bees, the inoculated poison has only local and transient effects for most people, but it can cause even fatal anaphylactic reactions in allergic subjects.
As aforesaid, the bumblebees are often subject to destruction through the demolition of the nests, sometimes necessary, and therefore it appears as a species potentially at risk.
For this reason, in some European countries, as in the case of Germany, a law of 1 January 1987 stipulates that burning fire with hornet nests is illegal, and carries the risk of incurring a fine.
However, in the case in which the high presence of the Vespa crabro causes particular problems to the bees or to cultivations it can proceed to its numerical containment. In general, the best solution is to identify the nests and report them to the authorities (fire brigades, agriculture, environment, health).
Even the beekeeping institutions and associations are obviously concentrated above all in the eradication of the Velutines or Asian hornets (Vespa velutina Lepeletier, 1836) but do not underestimate the presence of the hornet.
Some types of traps can be used to catch the hornets; these can be:
– adhesive (mistletoe type), self-made;
– by drowning; made with a container for the bait and a cover of various types that allows the entry but not the exit of the harmful insect, both ready on the market, either completely self-built, or with one of the caps on the market screwed onto the container standard food (bottle or glass jar);
– passive mechanics (specific for beekeepers), additional drawers to beehives, nets, etc .;
– luminous fans or a dazzling grid (as for mosquitoes, a bluish-cold light lamp attracts insects towards an aspirator or a lightening network);
– pharmacological (poisons): only for interiors infested with harmful insects or subject to their incursions, not to be used outdoors because they are also harmful to bees;
– biological: carnivorous plants specialized in flies and Asian hornets (in experimental phase).

Guido Bissanti

Sources
– Wikipedia, the free encyclopedia.
– Russo G., 1976. Agrarian Entomology. Special Part. Liguori Editore, Naples.
– Tremblay E., 1997. Applied entomology. Liguori Editore, Naples.

Photo source:
– https://inaturalist-open-data.s3.amazonaws.com/photos/261347860/original.jpg