Asian Hornets in September–October 2026: The Danger Peak Nobody Sees Coming

There is a precise moment in the year when the nature of our call centre changes. Until the end of August, people ring us about bed bugs, cockroaches, mosquitoes. Then, somewhere around 5 September, the calls flip: "there's a grey ball in the lime tree, we'd never seen it before", "my husband trimmed the hedge and got stung four times", "we can't go out on the terrace any more, there are a dozen of them around the compost bin".

This shift is no calendar coincidence. It corresponds to a very concrete point in the biological cycle of Vespa velutina nigrithorax, the Asian hornet, and it explains why September and October account for the overwhelming majority of serious stings and nest destruction call-outs in France. We are going to explain this mechanism, because it directly determines what to do — and above all what never to do — when you discover a nest right now.

Double bed with a bare white mattress in a grey bedroom, bedside tables and pendant lights

Why the colony becomes dangerous now and not in June

A population curve that explodes at the end of the season

The cycle of an Asian hornet colony lasts one year. A queen emerges from hibernation in February–March and builds a small primary nest on her own — first the size of a tennis ball, then of a grapefruit — often under a garden shelter, in a shed, beneath the eaves, sometimes inside an electricity meter box. She lays eggs, rears her first workers, and from May–June onwards the colony becomes self-sufficient.

Then comes the move. When the primary nest becomes too cramped, the colony migrates to a secondary nest, usually high up: 10, 15, sometimes 20 metres up in a broadleaf tree. It is this nest that, by September, reaches a diameter of 40 to 80 centimetres and commonly houses 1,500 to 2,000 individuals, with documented peaks well beyond that.

In other words: in June, a nest contains a few dozen workers and nobody notices it. In September, the same nest contains a small town, and that same colony has an entirely different tolerance for disturbance.

End-of-cycle stress

From late August onwards, the colony switches programmes. It gradually stops producing workers and shifts to producing reproductives: future queens and males. This production is extremely costly in protein. The workers therefore intensify their hunting — hence the pressure on apiaries, widely discussed by beekeepers every autumn — and become far more reactive to any vibration or movement near the nest.

The defence zone, which is a few metres in spring, expands in autumn. Field data and the recommendations of the Muséum national d'Histoire naturelle, which has coordinated monitoring of the species in France since its accidental introduction in 2004 in Lot-et-Garonne, converge on a safety perimeter of at least 5 metres, to be extended to 10 or 15 metres in the case of noisy work (hedge trimmer, chainsaw, leaf blower, scaffolding).

This is exactly what explains the typical accident profile we see: they are almost never walkers stung "at random". They are people who were trimming a hedge, picking apples, cleaning a gutter or running a brushcutter under a tree. The colony does not attack, it defends.

Recognising the Asian hornet — and not destroying the wrong insect

We stress this point because every autumn we see European hornet (Vespa crabro) nests destroyed for nothing, whereas that species is useful, far less aggressive, and locally protected by decree in certain départements.

The most reliable detail, visible even at medium range: the yellow-tipped legs of the Asian hornet, hence its nickname "yellow-legged hornet". A second decisive clue: if you see a large hornet flying around an outdoor lamp at 11 p.m., it is a European hornet. The Asian hornet is strictly diurnal.

If doubt persists, a pair of compact binoculars lets you observe the nest entrance from a safe distance — the lateral opening, on the side of the sphere, is characteristic of the velutina secondary nest, whereas the European hornet opens its nest from below. An identification guide to the insects of France also remains a reasonable investment for anyone living in the countryside or owning a large garden, and prevents plenty of needless panic over a simple paper wasp.

The moment when nests "appear"

Many calls begin with "the nest was built overnight". This is false in 100% of cases. A 60 cm nest represents months of work. What changes, in October, is the foliage: the first falling leaves abruptly reveal a structure that had been there since July, fifteen metres up, invisible.

Hence a simple prevention rule for owners of wooded plots: do an inspection round with your eyes upward in mid-October, when the trees are starting to thin out but the colony is still active. It is the best observation window of the year.

What you must never do when faced with a nest

Here we list the actions that cause most serious accidents. None of them is theoretical: we have seen every one of them.

• Never shoot at it. A shotgun is used every year; it scatters the colony over several hundred metres without destroying it, and leaves thousands of furious individuals in an inhabited area.
• Never burn a nest. Major fire risk in a tree or roof, and zero effectiveness: the nest's paper-like material burns poorly, and the workers come straight back out.
• Never use a hose or high-pressure jet. This triggers a massive defensive response with an operator stranded on the ground.
• Never spray an off-the-shelf insecticide aerosol from a ladder. Consumer "wasp and hornet" aerosols have a range of 4 to 6 metres and do not deliver the dose needed for a colony of 2,000 individuals. You end up with a partially affected, highly aggressive colony, and you are balancing on a rung.
• Never block the entrance of a nest in a cavity (roller shutter box, chimney, cavity wall). The hornets will come out through the inside of the building.

A single Asian hornet sting is no more toxic than a wasp sting. The danger comes from the number of simultaneous stings, and from the risk of allergy. That is why the rule is never to turn a nest into a battlefield.

Close-up of a brown-furred rodent, snout and whiskers visible, on stones outdoors

Stung: what to do within the hour

The recommendations relayed by Ameli and Vidal for hymenopterans apply to the Asian hornet.

For an isolated sting, with no history of allergy:

1. Move away from the nest immediately, calmly, without sudden movements — running while waving your arms makes the pursuit worse. Take shelter indoors or in a vehicle.
2. The hornet does not leave its sting behind (unlike the bee): there is nothing to remove, but check anyway.
3. Wash with soap and water, disinfect.
4. Apply cold — a reusable gel pack, to be kept in the freezer in any house with a garden, effectively reduces swelling.
5. Bringing a heat source close (an extinguished cigarette end held at a distance, or hot air) for a few seconds can degrade part of the heat-sensitive venom; it is a supplementary measure, not a treatment.
6. Monitor for 24 hours. Redness and local swelling of several centimetres are normal and last 24 to 48 hours.

Call 15 immediately if:

• multiple stings (from around ten in an adult, fewer in a child);
• a sting in the mouth, throat or near the eye;
• swelling of the face or lips, difficulty breathing or swallowing, generalised hives, faintness, vomiting → suspected anaphylactic shock.

People already diagnosed as allergic to hymenopterans must carry their prescribed adrenaline auto-injector pen at all times, and know how to use it. Desensitisation (allergen immunotherapy) exists and is covered by health insurance: it should be discussed with an allergist, ideally in winter, outside the exposure season.

Having a nest destroyed: who do you call, and who pays?

This is the question that comes up every single time, and the French answer is, let us be blunt, confusing.

The regulatory status

The Asian hornet is classified as an invasive alien species and appears on the list of category-two health hazards for the honeybee. The law of 20 February 2025 on combating the Asian hornet established the principle of a national control plan and a funding framework, but implementation still varies enormously from one département and one municipality to the next.

Practical consequences:

• Nest on public land (municipal tree, street furniture, school): it is up to the municipality to act. Report it to the town hall.
• Nest on private property: the costs are, as a general rule, borne by the owner. Many municipalities and inter-municipal bodies do, however, offer partial coverage, often 30 to 50% of the invoice, sometimes a flat-rate amount. So the reflex should always be: call your town hall before arranging an intervention, to find out about the local scheme and, often, the list of approved companies.
• In a co-owned building: a nest located in the common areas (a tree on the estate, a façade, a roof) falls to the managing agent, under the obligation of upkeep and safety.

One point we flag every year: the fire brigade no longer intervenes for hornet or wasp nests on private property, except in cases of proven imminent danger (a nest on a school in use, a stung person trapped, etc.). Dialling 18 for a nest in a cherry tree will get you, at best, a referral to a company.

What a proper intervention looks like

A serious destruction rests on three elements: a full Asian-hornet-specific protective suit (standard beekeeping outfits are not enough, as the velutina sting measures up to 6 mm and goes through single-layer fabric), a telescopic injection pole allowing treatment at 15 or 20 metres from the ground, and an approved insecticide with an almost immediate effect on the entire colony.

The intervention is best carried out early in the morning or at the end of the day, when all the foragers have returned. A treatment at midday leaves several hundred workers outside, and they will come back circling the site for days.

Removing the nest is not always essential — a treated nest is never recolonised — but it is recommended when accessible, to avoid later confusion and the structure falling. In Île-de-France, expect an order of magnitude of €90 to €250 depending on height and difficulty of access, before any municipal subsidy.

Prevention for 2027: spring trapping, with plenty of caveats

This is the most divisive subject. Mass trapping in autumn, using non-selective traps, is counterproductive: it mainly captures native insects (wasps, flies, moths, hoverflies) for a negligible impact on colonies. Both ANSES and the Muséum have called for caution regarding these practices.

Useful trapping is targeted, localised and carried out in spring: from February to May, around apiaries or a site where a nest was destroyed the previous year, using selective hornet traps fitted with calibrated entry holes (8–9 mm) and exits for small insects. The classic bait combines dark beer, fruit syrup and a little white wine — the latter repelling bees. Traps must be checked regularly and removed as soon as June arrives.

Three other measures deliver a far better return than trapping:

• inspect garden shelters, sheds, under-roof spaces and shutter boxes in spring, where primary nests take hold: at that stage, a nest the size of an orange can be neutralised without significant danger, early in the morning;
• protect apiaries with anti-hornet muzzles fitted to the landing boards, and raise the hives;
• cover compost bins and food-waste bins, and pick up fallen fruit — an unharvested orchard in September is a magnet for hornets and wasps.

Hornets' nest hanging from the bare branches of a tree against a blue sky

And where do things stand in Île-de-France?

The species, present in the Paris region since the early 2010s, is now established across all its départements. Nests are concentrated in wooded residential areas, parks, cemeteries, allotment gardens and railway land — anywhere large broadleaf trees sit alongside sugar and protein resources.

The density is not that of the South-West, but the Île-de-France peculiarity lies elsewhere: the proximity between nests and human activity. A nest 12 metres up in a plane tree is unremarkable in a rural area; the same nest above a playground or a restaurant terrace in September is a matter of collective safety.

Our operational recommendations for this end of season:

1. Look up in your garden, your building's courtyard, the areas around your school, between mid-September and the end of October.
2. Report any suspicious nest on the national Asian hornet reporting platform and to your town hall — the data feeds into the monitoring coordinated by the Muséum.
3. Postpone pruning and trimming work within a 15-metre radius as long as the colony is active. After the first sustained frosts, the colony dies and the nest becomes inert.
4. Take no personal risks. A colony of 2,000 individuals 15 metres up is not a weekend DIY project.

The Asian hornet will not disappear from France: it is now an established species, and the realistic goal is local management, not eradication. But between leaving an active nest above a children's play area and getting out the insecticide spray on a ladder, there is a reasonable middle ground: identify correctly, report, secure the perimeter, and have properly equipped people intervene at the right time.