The pine processionary caterpillar It is a lepidopteran insect that is given this name because of the curious way in which it uses its name caterpillars moving across the ground and forming characteristic rows or rows (“processions”).
The pine processionary caterpillar es a moth or moth. It has a complex life cycle and that is why we remember them only in the winter and spring months, when we see their stage of development. stinging oruga. We explain it in general terms:
BIRTH OF THE ARNAS. When the first heat of summer arrives, the pupae that have spent the winter and spring buried are transformed into adult moths and are born during the day. At dusk they become active and fly to the tops of the pine trees, where they lay their eggs around a kind of cylindrical membrane that resembles paper.
HATCHING OF THE EGGS. The eggs hatch on the leaves of the host plant (plant chosen by the moth to lay the eggs), which in our country is mainly the black pine (Pinus nigra) and the Scots pine (Pinus sylvestris). The caterpillars feed on their narrow leaves, called needles because they look like needles, and so grow quickly.
GROWTH OF CATERPILLARS. The development of caterpillars is divided into five different stages. At each stage they must ‘shed their skin’ to grow and ‘dress’ in a different colour: first green, then pink, reddish and finally black with an orange hairy band on the back and white on the sides. The last two stages are the most voracious and can cause the trees to lose so many leaves that they appear to be dehydrated.
FORMATION OF THE BAGS. The caterpillars gather in white silky sacs once they are born. At first they go unnoticed, but at the end of autumn they are quite large and very easy to see at the tops of many branches, and they are essential to prevent the caterpillars from dying from the cold (we must remember that they don’t). generate internal heat as we do). They are your refuge. At the same time, they develop a series of stinging hairs to protect themselves against any possible predator, which can irritate our skin and mucous membranes (and those of other animals) and cause serious allergic reactions. It is the best known form of the procession.
PROCESSES AND BURIALS. With the arrival of good weather, the caterpillars descend from the treetops in single file, as if in a procession, and it is this behavior that gives them the name processionaria. The processions are always led by females and they all bury themselves in groups about 15-20 cm deep, underground where we lose sight of them. Once there, they form cocoons, where they move into pupae and enter a resting phase until conditions are optimal for them to emerge as butterflies during the summer. Did you know that during this phase they can wait underground for up to seven years to emerge as butterflies? And to make matters worse, after waiting so long, butterflies live an average of one day without even eating! They devote themselves only to fertilizing and laying eggs.
The pine processionary caterpillar is not a pest in itself
The density of the bags and the abundance of caterpillars varies each year depending on environmental conditions. Global warming is making conditions increasingly favorable for this species (milder winters and warmer springs), leading to more premature caterpillar emergencies and more severe damage to pine forests. However, we must not forget that the effects of the processionary caterpillar does not kill the pines immediately.
Because the caterpillars eat only the needles and do not touch the base of the leaf (bud), defoliation weakens them, but pine trees have shown us that they have the ability to recover. However, the problem arises when the damage continues over the years and can weaken them to such an extent that they are much more susceptible to other pathogens, to wounds or to droughts such as the one we have been experiencing for three years. . When these environmental stresses occur while the forest is weakened by the processionary caterpillars, they can eventually kill the pines, something we are already seeing in the central region of Catalonia.
All this must be taken into account the processionary caterpillar is not an external pest that invades the forest. It is a native species that has long been part of our country’s forest ecosystems and is fully integrated into the food web. It is food, in all vital phases (eggs, caterpillars, pupae and butterflies), for many predators: other insects, insectivorous birds such as tits, hoopoes, cuckoos…, bats, small mammals such as bat groups… which have a very play an important role, important for the population control of the species.
How to combat the pine processionary caterpillar?
There are several methods that allow controlling (not exterminating) pine processionary populations in case they affect pine forests in a very significant way, some more actively and others passively. They are the following:
- Check biological. Let nature itself be responsible for regulating the population. Bats can eat processionary caterpillars when they emerge from the ground and many bird species eat the caterpillars when they are in trees (such as blue tits) or when they are already buried (such as hoopoe). Therefore, additional measures can be applied to facilitate this, such as installing nest boxes to promote the presence of insectivorous birds and bats.
- Mechanical control. It consists of eliminating the bags with the caterpillars still inside them during the winter, by cutting the branches in which they are located, burning the bags or even shooting them with shotguns. Destroying the bags must be done professionally and with due care to avoid the effect of stinging hairs. On the other hand, in the case of gardens or forests with few affected trees, a less aggressive and equally effective method can be used: spiral rings. They are plastic rings placed around the trunk that guide the caterpillars into a bag where they eventually die. This prevents the caterpillars from descending the trunk and ending their life cycle.
- Pheromone control. The vast majority of animals use pheromones to attract the opposite sex and reproduce. In this case, traps containing female pheromones are placed to attract the males and thus prevent them from fertilizing the females.
The years in which the effects pine processionary caterpillar are very serious, the competent authorities often spray the forests with a solution of the bacteria using small aircraft. Bacillus thuringiensis var.kurstaki (BTK). Because this bacterium parasitizes the larvae of some insects, it can kill them processionary caterpillars and thus reduce its ability to attack the pines. Now this treatment should be reserved for the most severe cases, because it does not just kill the disease pine processionary caterpillarbut also affects other butterflies, flies, beetles and nematodes.