URL: https://www.waldwissen.net/technik/holzernte/arbeit/wsl_schmetterlingsraupen_brennhaare/index_EN
Originalartikel: Burri, M., Schniepper, M. (2006): Schmetterlingsraupen mit Brennhaaren. Merkblatt zu Arbeitssicherheit und Gesundheitsschutz in den Strassenunterhaltsdiensten. Herausgegeben von der Koordinationsgruppe Arbeitssicherheit im Strassenunterhalt (KGr AS SUD). www.nationalstrassen.ch
Autor(en): Monika Burri, Maja Schniepper (Gruner AG)
Online-Version: Stand: 16.09.2009
Redaktion: WSL, CH

Beware of caterpillars with urticating hairs

Some species of caterpillars have urticating hairs which can cause extreme itching, skin irritations and damage to eyes and the respiratory system. Therefore care must be taken during work being carried out along the edge of forests, on embankments or whilst tending trees.

Raupen des Eichenprozessionsspinners
Fig. 1 - Oak processionary moth caterpillars.
Photo: Entomology (WSL)
Raupen des Pinienprozessionsspinners
Fig. 2 - Pine processionary moth caterpillars.
Photo: Entomologie (WSL)

Occasionally during the course of maintenance work being carried out along the edge of forests or on street embankments health problems caused by three species of moths can occur. Contact with the stinging hairs of these caterpillars can lead to skin irritation and/or allergic reactions of the skin, mucus membranes or respiratory systems. The species in question are the following:

Why can these caterpillars be dangerous?

Most of us regard butterflies as colourful messengers of summer. Some people are aware that caterpillars can eat voraciously. For instance, the cabbage white dines in the vegetable garden. The mottled umber can damage fruit plantations by eating buds, leaves and blossom. The orchard ermine wraps up the left over bare wood and its surrounding area in white webs. Asian gypsy moth caterpillars manage to defoliate whole forests during their rare mass outbreaks and are a nuisance to people living near by when they move into gardens and houses by the hundreds or even thousands.

All of these species catch our eyes with their webs, nests and intense defoliation, but although they cause a certain amount of damage to cultivated plants they are however harmless from a health point of view.

The three aforementioned species are also noticeable thanks to their nests, webs, defoliation and caterpillar processions but they can also cause health problems. These caterpillars have stinging hairs which can cause itching, skin irritation and also eye problems or damage to the respiratory system.

What are urticating hairs and what is their function?

Gespinste des Pinienprozessionsspinners
Fig. 3 - Infestation of pine processionary moth caterpillars.
Photo: Entomology (WSL)
Raupe des Dunklen Goldafters
Fig. 4 - Gold tail moth caterpillar.
Photo: Beat Fecker (WSL)

Urticating hairs protect the caterpillars and their later stages of development (Pupae, moth, egg) from predators.

How does one come into contact with the hairs?

The urticating hairs of the golden tail moth, although less aggressive, are however used for protection in every stage of development: the hairs which are produced only by the caterpillars are woven into the pupae cocoons the female then strokes them onto her abdomen from where they make their way into the egg clutches during egg laying.

Symptoms and precautions

Skin irritations (caterpillar dermatitis)

One reaction after contact with stinging hairs of the gold tail moth may be extreme itching; this can occur hours after contact, but may continue over several days. Although only a slight rash occurs after contact with the gold tail caterpillar extreme itching can prevent a person sleeping. After contact with the stinging hairs of oak processionary or pine processionary moths the following symptoms may also occur:

In the case of processionary moths a further complication is that increased caterpillar contact increases the sensitivity and therefore the intensity of reaction of the affected person.

Symptome von Prozessionsspinnerhaaren
Fig. 5 - Possible results of contact with the stinging hairs of processionary moths.

Immediate measures to be taken when affected

In Switzerland health problems caused by caterpillars are treated by health insurance companies as accidents (analogue with tick bites).

Measures to be taken in infested areas

a) Assessment of the situation

After a situation has been assessed and it is clear that there is an infestation of caterpillars with urticating hairs then a plan of action will be prepared using the following guide lines:

b) Prevention measures

In areas infested by gold tail or pine processionary moths the total removal of all possible winter nests can provide infestation free areas which should last at least up until the following autumn.

Non dangerous species without urticating hairs

gewöhnlicher Wollafter
Fig. 6 - Small eggar.
Photo: Beat Wermelinger (WSL)
Fig. 7 - Ermine moth.
Photo: Beat Wermelinger (WSL)

Harmless species which have a similar biology and whose population could be endangered should not be controlled:

a) Small eggar

Wide spread in the canton of Wallis, otherwise sporadic in the cantons of Tessin, Bündner Rhine Valley, the area around Zürich, and in the Walensee area. Due to its rarity it should be protected. Nests should never be removed!

b) Ermine moths

Nine very similar species, generally very widespread.

Distribution and occurrence

The three species with urticating hairs were at one time more widely spread in Switzerland and more common. Their population was drastically reduced by the thoughtless use of insecticides in agriculture. In Switzerland and in near by neighbouring countries they are now once again on the increase. This increase is being encouraged by global warming. Distribution maps can be found in the leaflets (see download).

The pine processionary moth has been observed for some time in several areas in southern Switzerland. Since the beginning of the 1990’s there has been an increase in the appearance of the oak processionary moth and the dark gold tail moth: with the oak processionary moth occurring more rarely than the dark gold tail moth. All three species are capable of mass reproduction.