Espais Verds

During the winter months we can see groups of the pine processionary by pine trees in some woodland areas in parks and green spaces in the city.

Its presence generates some concern among people as it can be irritating and harmful if it comes into contact with the skin. The species can be seen in groups when its larvae come down from trees to bury themselves. This means the pine processionary can often become a problem associated with urban greenery in cities and their metropolitan areas.

Because of this, we want to explain what sort of pest we are talking about and what we are doing at the Municipal Institute of Parks and Gardens to control it.

What is the pine processionary?

The pine processionary (thaumetopea pityocampa) is a moth species that basically feeds on the coniferous leaves of the Pinus and Cedrus genus.

The most significant effect of the insect on coniferous forests is the recurrent large loss of foliage, affecting the development of forest mass.

How do they affect us?

The effects of this insect for human health, and particularly for the health of dogs, come when the moth is in its caterpillar stage. The caterpillar’s hairs are irritating and can cause strong allergic reactions.

In this respect, the most harmful point for members of the public is when the caterpillar is in the process of going to ground and burying itself, coming down from the tree trunk and forming typical processions (hence the name) as it searches for the most suitable spot to bury itself for its pupal stage.

This stage normally starts around February and continues until April. The duration of the different stages can vary depending on the weather conditions.

Where can we find it in Barcelona?

The areas most affected are the green spaces in the neighbourhoods close to the Collserola mountain range, the adjacent hilltops and the mountain of Montjuïc, given that these spaces have the main concentrations of conifers.

What are we doing to tackle it?

The fight against this insect mainly involves measures that are not very aggressive, so that there are no risks for members of the public.

The Barcelona Municipal Institute of Parks and Gardens, tasked with managing the city’s greenery, carries out two types of action: prevention and cure.

Preventive measures

Traps are put out around July to capture pine processionary adult moths. One example was the exercise carried out in the woodlands of the Parc del Guinardó this summer, the goal being to gauge the spread of the moth and the existing volume of individuals.

Trunk injection treatments are carried out in October on pine trees in sensitive areas (near children’s play areas, dog areas and picnic areas). This method allows insecticide to be directly introduced into the sap of the tree, without the product coming into contact with the outside.

Towards the end of December, all the city’s pine tress are treated using spray cannons with and conventional authorised low-toxicity plant protection products.

Nesting boxes are also placed in affected areas. Some insect-eating birds (the blue tit, the cuckoo and the hoopoe) help towards biological control and act as predators for pine processionary caterpillars.

Cure measures.

In terms of solutions to cure the problem, these are carried out when the previous treatments have not had the desired effect and the larvae survive the preventive actions. This means the insect develops and builds a ball or a nest at the end of the branches to protect itself from the cold.

The first action is to hang up warning signs for the public, explaining the basic prevention measures. Next the pine processionary nests are removed using an elevation platform before the affected tree is treated by spraying it.

Where the caterpillars are on the ground, staff use protective equipment and remove them.

Biological control trial

The Municipal Institute of Parks and Gardens teamed up with the CREAF (Ecological Research and Forestry Applications Centre) in 2020 to conduct a biological control trial on the pine processionary in the urban environment in Barcelona.

Six sites were selected for monitoring the work: woodland spaces in the parks of Montjuïc, Can Sentmenat, Castell de l’Oreneta, La Creueta del Coll, Guinardó and Turó de la Peira.

Based on the results, the pine trees found to be repeatedly affected during the trial were treated with trunk injections in December. These treated trees are being labelled in January, along with trees detected with processionary nests.

And you? What can you do?

Public collaboration is very important for controlling the pine processionary. Members of the public can report and help with the detection of this pest in green spaces (gardens and woodland areas). This allows us to locate the points affected and to act more swiftly.

You can report any incidents linked to the pine processionary here.