Thaumetopoea processionea

Thaumetopoea processionea

Thaumetopoea processionea (Polilla procesional del roble)

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The larvae or caterpillars of the oak processional moth (OPM, scientific name Thaumetopoea processionea) can affect the health of oaks, people and animals. They feed on oak leaves, and large populations can strip the trees, leaving them weakened and vulnerable to other threats. A substance in the small hairs of caterpillars can cause skin and eye irritations, sore throat and breathing difficulties in people and animals that come into contact with them.

The species derives its common name from the fact that the caterpillars live mainly in oaks and move in processions from nose to tail; derives the first part of its scientific name from thaumetopoein, the irritant protein in the hair of the caterpillars.

In the United Kingdom, it is known that OPM is only present in London and some neighboring counties, and in West Berkshire. It is subject to a survey and control program led by the government in these areas to minimize populations, dissemination and impacts.

The carefully controlled treatment of affected trees with approved insecticide to kill caterpillars when they were still young enough for effective treatment was carried out in late spring and early summer. Next, a summer survey was conducted for, and elimination and destruction of nests in the Control and Protection Zones. The owners of oaks in the Core Zone were strongly encouraged to do the same.

The caterpillars completed the pupation on adult moths in their nests on the trunks and branches of the oaks at the beginning of September. During this period, once again, we made the capture of pheromones of male moths, which can alert us to possible changes in the distribution of the pest.

Health precautions: tips to avoid contact with the caterpillars.

The nests can occur in a variety of ways, including hemispherical (half ball), tear-shaped, bag-like, and like a blanket stretched around a part of the trunk or branch. Sizes range from as small as the width of a 50 pence coin to several meters above the oak trunk in some cases. They can occur from the ground level to the top of the oak, and can fall from the oaks and be on the ground.

The caterpillars rest in these nests during the day between the feeding periods, and later in the summer they retreat to the nests to become adult moths.

Adult moths emerge from pupation and are active from mid to late summer, and lay their eggs on twigs and small branches in oak trees. They are a little distinctive brown moth, very similar in appearance to other harmless species, and due to the difficulty of identifying them accurately, we do not require reports of moth sightings.

The key identifying characteristics are that the larvae (caterpillars):

move in processions from nose to tail;

often they form processions with arrowhead, with a leader and subsequent rows containing several caterpillars at the same time;

they are more likely to be found in oaks, and sometimes on the ground under oak trees;

they are more likely to be seen in summer;

it has very long and white hairs that contrast sharply with other shorter hairs; Y

do not live in fences, walls and similar structures, as some species of caterpillars do.

For people and animals: the caterpillars have thousands of hairs that contain a stinging or irritating substance called thaumetopoeina, from which the species derives part of its scientific name. Contact with hairs can cause itchy skin rashes and, less commonly, sore throats, breathing difficulties and eye problems. This can happen if people or animals touch the caterpillars or their nests, or if the hairs come in contact with the wind. Caterpillars can also shed hairs as a defense mechanism, and many hairs are left in nests, so nests should not be touched without protective clothing.


touching or approaching nests or caterpillars;

allow children to touch or approach nests or caterpillars;

allow animals to touch or approach nests or caterpillars; or

Try removing nests or caterpillars yourself.

Data sheet
45 days / 6 weeks


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Thaumetopoea processionea

Thaumetopoea processionea (Polilla procesional del roble)

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