The common hornet (scientific name Vespa crabro) is a species of large wasp with a black, yellow and brownish-red striped body. It should not be confused with similar insects in the bee family such as the bumblebee and carpenter bee, nor with wasps such as Vespa orientalis (also called the Oriental hornet, despite being native to Italy) and Vespa velutina (Asian hornet or yellow-legged hornet).
The life cycle of hornets begins in spring, when the queen begins building a nest. The first eggs hatch into sterile female workers. From that point on, the queen dedicates herself to laying eggs, while the workers tend the colony and enlarge the nest. Males and fertile females hatch later in the summer. The queen, workers and (after mating) males die in the autumn. Only fertilised females survive and hibernate over winter, before going on to found new colonies the following year.
Sometimes the habits of these insects interfere with our lives, making them dangerous. In this article we tell you how to get rid of hornets safely when necessary and how to prevent them spreading in your house and garden.
Hornets: habits, advantages and hazards
Hornets are predators that feed on other insects, but they also like sugary foods such as nectar and ripe fruit. They can ruin the harvest of your fruit trees—cherry, fig, pear, plum and so on—or vines. Although they attack the precious honeybee, they are still a valuable part of the ecosystem, and therefore useful for gardens and even orchards, insofar as they hunt harmful insects such as flies, caterpillars, grasshoppers and wasps, and are also pollinators.
To debunk a common myth, hornets are not particularly aggressive—they are less aggressive than their smaller cousin, the common wasp—except in certain situations. They tend to avoid humans, rarely entering busy rooms or landing on laid tables, and fly away if threatened. However, if you try to swat them or approach too close to their nest, they can react aggressively.
Only females have a sting and it is quite painful due to the amount of poison they inject. The pain is normally limited to the sting site, but people with allergies can suffer a more intense localised reaction or even generalised swelling. In serious cases this can cause breathing difficulties and anaphylactic shock, which is potentially fatal although rare, occurring in 1 case/million population per year.
Like bees, hornets are social insects. Their nests are fascinating, paper-like spheroid structures that can also reach impressive sizes. Made up of several overlapping honeycombs covered in a casing and with the entrance at the bottom, they are made from a mixture of chewed wood and saliva.
Where do they prefer to build their nests? Hornets seek out warm, sheltered and undisturbed areas, often inside existing natural or man-made cavities, such as in cracks or holes in the outer walls of houses, chimney flues, attics, cavities, false ceilings and roller shutter boxes. The nests can be attached to cornices and eaves or hidden under windowsills. Hornets also take refuge indoors or in outbuildings such as log stores and tool sheds, as well as outdoors in hollow trees, stumps and birdhouses.
When and how to exterminate hornets
It is not always essential to eliminate hornets with insecticide, although it must be done if they pose a genuine threat to people. The ideal strategy is to prevent and stop them from multiplying. One of the systems you can adopt is hanging traps from branches and between trees from the beginning of spring (in orchards, don't wait until the fruits ripen). This is the best time to capture the queens before they can produce a new generation of hornets. For more details about hornet traps and various preventive measures, see the last part of this article.
So what should you do when you find a hornet's nest in your house or garden? First, keep a safe distance of at least 5 m, to lessen the risk of being attacked by a swarm and suffering multiple stings, which can lead to a serious physical reaction even if you are not allergic to the venom.
Evaluate the situation thoroughly before deciding how to eliminate the hornets and remove the nest. If it is small and in an easily accessible place (maximum height or distance 4-5 m), consider exterminating the hornets yourself. Otherwise, it is advisable to call up a pest control company, which will have all the equipment needed to do the job safely. Alternatively, contact your local council, which should be able to offer paid pest removal services. Find out if your local authority provides this type of service. Here in Italy it is delivered by civil protection volunteers. Bear in mind, however, that, for problems of this type on private properties, the fire brigade will only intervene in specific cases.
Have you decided to remove a hornet's nest yourself? If so, exercise caution and do it from a distance:
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Buy a long-range insecticide spray that specifically targets hornets, ideally a foam spray. Don't use products intended for other insects, as they are less effective and their slow action can give hornets sufficient time to sting you. In outdoor environments, you can use pyrethroid-based liquid insecticide and distribute it with a backpack mistblower (here is a video showing how to use one correctly).
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Protect yourself from stings by wearing an extra layer of clothing, an overall in non-woven fabric, a beekeeping hat with head net, and gloves.
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Spray early in the morning or in the evening, when most hornets are in the nest (they are typically diurnal insects).
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Spray the insecticide from a distance, first on the outside of the nest and then inside, through the entrance, in order to deter attack by the hornets.
At this point you can remove the hornet's nest, wrap it in a plastic bag and clean the remains. If possible, block all access routes to the cavity or room in which the nest was built, using mosquito nets or other solutions (you can find further information about this in the last part of the article).
A solution that we recommend not to adopt when removing a hornet's nest is to burn it after having sprayed it with insecticide or flammable liquids, or using a blowtorch.
How to prevent hornets nesting in roller shutter boxes etc.
Having looked at the best ways to tackle hornets nests, let's now move on to tips for preventing the establishment of nests in roller shutter boxes and other places that these insects prefer. It’s worth knowing that hornets never reuse an old nest, but if you remove it, they will readily build a new nest in the same location:
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Check: regularly inspect places where hornets might nest, which is most often in hollow trees, attics and inside chimney flues. If you see a hornet in the garden, try to work out which direction it came from (and therefore where the nest is): observe whether it crawls into any opening in the house, or hides in a tree in the garden.
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Selective traps: there are various types, among which drowning traps are very effective. They lure hornets into a kind of funnel from which they cannot escape, then drown them in a liquid that serves as bait. You can buy them or even make them yourself, for example by repurposing empty plastic bottles. For the sugary bait you can use various home-made formulations based on beer, vinegar or wine and, of course, sugar or honey.
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Trees: evaluate whether to seal cavities formed by badly healed cuts. For example, lime mortar and sawdust were traditionally used, but treating cavities this way is rather controversial.
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Order: keep the garden, attic, woodshed, tool shed, etc. as tidy as possible.
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Tree stumps, logs etc.: dispose of them or use them as firewood. To uproot and split a log you need a hatchet, chainsaw, hoe, spade, wedges and sledgehammer. Before moving a log to saw off pieces to put in your kitchen stove, check that it isn't sheltering a hornet's nest.
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Access routes: seal cracks in walls and false ceilings, and install mosquito nets over windows, air vents and similar fixtures in the attic or tool shed.
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Chimney flue: a hornet's nest can block the escape of fumes from boilers and stoves. Therefore, clean your chimney flue regularly and if it is not in use, cover the opening with a mosquito net.
In addition to hornets, the garden is populated by other dangerous insects: here you will find a focus article on processionary moth caterpillars and one on fleas. On the subject of potential damage to fruit trees caused by hornets, at the start of the article we mentioned vines. These plants are also vulnerable to specific diseases, one of the main ones being powdery mildew: here's how to prevent and treat it.
