C-DRONE GUIDE · 10 AUGUST 2026
Drone Survey of Pine and Oak Processionary Moth Nests: 2022 Legal Obligation and Price
A line of brown, hairy caterpillars filing across a schoolyard, a campsite lane or a hiking path is enough to alarm any site manager: both the pine and the oak species carry urticating hairs capable of triggering skin, eye and sometimes respiratory reactions on contact or simply by inhalation — a study by Vega, Vega and Moneo published in 2011 in Actas Dermo-Sifiliográficas details these clinical manifestations in humans. Since decree No. 2022-686 of 25 April 2022, both species have been listed among the pests harmful to human health under Article L. 1338-1 of the French public health code, which lets prefects require owners, tenants and managers of infested land to act. Spotting every nest before it matures — ideally in winter, when it stands out clearly against a pine's canopy or an oak's bare branches — remains the first step of that response. Here is what this obligation covers, what a drone survey can document, and what it costs in 2026.
Published on 10 August 2026, reviewed on 10 August 2026 — regulations in force as of August 2026.
A pest officially "harmful to human health" since 2022
The pine processionary caterpillar (Thaumetopoea pityocampa) and the oak processionary caterpillar (Thaumetopoea processionea) spin a conspicuous whitish silk nest at the tip of branches in autumn, where the caterpillars gather by day before coming out at night to feed on needles or leaves. Decree No. 2022-686 of 25 April 2022, issued under Article L. 1338-1 of the French public health code, added both species to the list of organisms whose proliferation is harmful to human health (Article D. 1338-1 of the same code). This listing lets prefects issue orders defining a geographical zone, an intervention timetable and authorised control methods, which owners, tenants, operators and managers of infested land must then apply within the set deadlines — an obligation that primarily concerns municipalities for their green spaces, schools and pine- or oak-lined roads, but also campsites, golf courses and residential estates.
The risk comes from microscopic urticating hairs that the caterpillars release as soon as they feel threatened, capable of drifting on the wind for several dozen metres around the nest. A study by Vega, Vega and Moneo published in 2011 in Actas Dermo-Sifiliográficas reviews the clinical manifestations observed after exposure: an itchy skin rash within an hour of contact, conjunctivitis if hairs reach the eye, and, more rarely, upper respiratory tract effects after inhalation (see the study on Google Scholar). According to the same study, contamination occurs mostly in pine forests, peaking between March and May — the period when mature caterpillars leave the nest to burrow into the ground before turning into moths, releasing the largest number of urticating hairs in the process. This risk affects both site users — children in a schoolyard, holidaymakers under a campsite's pines — and pets, whose muzzle and tongue are especially exposed when they sniff a caterpillar on the ground.
Why a ground survey quickly reaches its limits
A pine processionary nest is most often built around the edge of the crown, sometimes more than fifteen metres up on a tall pine, and blends into the foliage as long as the tree stays green — only in winter, once needle density drops or the oak sheds its leaves, does the white nest stand out clearly. A walking survey, binoculars in hand, quickly reaches its limits: it struggles to cover a long roadside row of trees, a green space spanning several hectares or an entire pine forest, and frequently misses nests invisible from the ground, particularly those built at the top of the crown or on the side facing away from the observation path.
A study by Garcia, Samalens, Grillet, Soares, Branco, van Halder, Jactel and Battisti published in 2023 in the journal NeoBiota tested two automated deep-learning detection methods (R-CNN and YOLO) on aerial drone imagery, across three forest-stand configurations in southern Europe: the YOLO algorithm delivered the best results, and the authors conclude that a drone can document the presence of at least one nest per tree with a reliability that ground observation alone does not reach (see the study on Google Scholar). Flown a few metres from the crown, a camera-equipped drone offers a vantage point that neither a walking survey nor ground-level photos can match over an extensive site.
What a drone survey adds: counting, geotagging, mapping
The flight follows a survey plan over the row of trees, the woodland or the green space in question, at a distance and altitude adjusted to distinguish a nest from the surrounding foliage — ideally between November and February, once nests have reached their final size and stand out best. Each nest found is geotagged and plotted on a map of the site, with an estimate of its size and height in the tree; this georeferenced count can be compared year on year to track how the infestation evolves and prioritise which areas to treat first. This survey-before-intervention logic mirrors our guide on drone detection of Asian hornet nests: in both cases, the drone documents the scale of the problem before a professional intervenes on the ground, never replacing the treatment itself.
On municipal tree stock already mapped — see our guide on drone tree inventories for municipalities — this survey adds a further health-risk indicator to each tree's record, alongside the fall-risk assessment some local authorities already track. For a school, this survey can also be combined with a flight already planned in spring for other purposes, as described in our guide on schoolyard thermal audits, cutting down the number of flights needed on the same site. The report delivered to the site manager lists the nests found, their precise location and their accessibility, giving a usable file to hand to the pest-control or biological-treatment company that intervenes next — pheromone traps, trunk-mounted eco-traps, or a Bacillus thuringiensis biological treatment depending on the season and local regulations.
Flight framework and 2026 pricing
These missions usually fall under the open category, after checking the Géoportail restricted-zone map — a schoolyard, a municipal green space, a campsite or a roadside row of trees generally raises no particular airspace constraint beyond the usual height and third-party distance rules. Flying over an active schoolyard or campsite nonetheless calls for informing the establishment or operator beforehand, if only to schedule the flight outside busy hours. As with any professional service, all-risk drone insurance covers the pilot in case of an incident above a site used by the public.
Ranges observed in 2026 (excl. VAT), depending on the area covered and the number of trees to examine:
| Service | Observed price (excl. VAT) |
|---|---|
| One-off survey (schoolyard, roadside row up to 30 trees) | €150 to €350 |
| Mapping of a municipal green space or small woodland | €350 to €700 |
| Multi-year monitoring (several passes, year-on-year comparison) | lower per-pass rate, quoted |
| Multi-site campaign for a local authority (several schools, parks) | 10 to 20% discount per site |
Request a quote stating the area to cover, the number of trees involved and the desired timing.
Does the drone also treat the nests it finds? No: the service documents and geotags the nests; treatment (mechanical removal, trapping, biological control) is still carried out on the ground by a specialised company.
Can an owner be forced to act? Yes, as soon as a zoned prefectural order applies to their land: the 2022 decree lets the prefect impose a deadline and a control method on the owners, tenants and managers concerned.
When is the best time for a survey? Winter, from November to February, when nests have reached their final size and stand out best against foliage or bare branches — before caterpillars descend to the ground in late winter, the period when the urticating-hair risk is highest.