Caterpillar nests will now be evident in Majorca. | Archive

If you haven't encountered them yet, you soon will do - it is the processionary caterpillar season.

While measures are taken to try and minimise their harmful effects in late winter, e.g. by shooting down nests, preventive action is organised for October. The forest health service, a department within the environment ministry, is already preparing to treat some 6,000 hectares of pine wood with a biological agent sprayed from the air. This treatment doesn't affect bees, it doesn't linger and is compatible with general agricultural ecology.

The director of the service, Sandra Closa, says that priority is given to areas with the highest levels of infestation, to areas where pine woods are being killed off and also to areas most frequented by the public.

There is a system of declaring plague zones, with the islands mapped according to their infestation levels. The maximum grade five level is limited to only a few parts of Majorca, e.g. in Manacor. Grade four is more common and is particularly evident in the south of the island to the east of Palma. Much of the Tramuntana is only lightly infested.

Plagues have existed in Majorca and Minorca since 2014 and in Formentera since 2016. There has been no plague declaration in Ibiza, but the forest health service is nevertheless going to undertake aerial spraying there this autumn. Closa explains that it is impossible to have total control and eradicate the caterpillar. Each moth lays 300 eggs on average. Keeping the number of caterpillars to "tolerable levels" is about the most that can be achieved.

The government's measures are directed at public land. For private individuals, Closa says that cutting the nests down (either by shooting them down or other means) and then setting fire to them is the best method right now. Traps to capture moths are the best means in the summer.