How dangerous it is to be an arborist

Processionary moth - danger to trees, hedges and gardens

While the butterfly shape isn't a problem for gardens, hedges, and trees, it is Caterpillar shape a danger to humans, animals and the garden. The caterpillars have long and short hair. The long hair poses no danger, while the short hair is dangerous for humans and animals. If the short hair comes into contact, it can penetrate the skin and cause allergic skin reactions. The hairs of the caterpillars are also known as stinging hairs and the caterpillars themselves are known by names such as hair caterpillars, nettle worms, pulling caterpillars or nettle worms.

Way of life and the danger to gardens and trees

The Processionary moth is also known as the oak processionary moth, which already indicates the way of life of the butterfly. The animal lives on oaks and can be found in Germany on English, red, columnar and sessile oaks. The caterpillars can be found especially in early summer in forests with oaks and under oaks in gardens. Particular caution is then required for humans and animals. At this time, the caterpillars are particularly active and can cause an allergic skin reaction with their stinging hairs.

The females lay their eggs on thin, sunny crown branches in autumn. The caterpillars hatch and eat the leaves of the oaks only in mid-April. The caterpillars wander up and down the trunk of the oak to get to the best feeding places. The hike in groups is like one procession, which is why the insect bears the corresponding name. The processions can be up to ten meters long.

The spinning of nests is characteristic of the caterpillars. The nests are used for pupation, but also as a place of retreat during the day. The moths of this insect species hatch in August and have a life expectancy of a few days. The moths lay eggs during their short lifespan.

The caterpillars are very voracious and therefore not without problems for the infested oaks. The webs, as well as the caterpillars themselves, should be controlled in private gardens and in public areas. The dangerous stinging hairs cause health problems in humans. The removal of caterpillars and webs must be carried out professionally and should not be carried out by private individuals. The webs can still be dangerous for humans even after a long period of time due to the remains of caterpillars that have fallen off or left behind. The Oak processionary moth forms the stinging hairs as protection against predators.

Oak processionary moth - dangerous for humans

The danger from the stinging hairs of the caterpillars does not only occur on the oak itself. The hair can break quickly and, if there is wind, appear in an extended area of ​​the infested trees. The hair is, for example, on bushes or on the ground. The danger exists in the vicinity of infested oak trees all year round. The hairs remain in the nests even after the moths hatch and can health problems cause. If nests, hair and caterpillars are to be removed, extreme caution is required. Protective suits and special protective measures are essential for removal.

Thaumetopoein is the name of the poison carried by the hair of the caterpillars. The poison is one of the protein poisons and causes skin rashes, fever, dizziness, eye irritation and other allergic reactions. An allergic shock can even occur. Furthermore, bronchitis and asthma can be triggered by the poison. It is known that the more people come into contact with the hair, the worse the reactions to the poison can be. Anyone who has come into contact with the hair of the oak processionary caterpillar should consult a doctor. The doctor may prescribe ointments containing cortisone or other remedies for the allergic reactions.

Interesting facts about the stinging hairs of the caterpillars

The hair of the caterpillars is dangerous for humans from the 3rd larval stage and can lead to inflammatory and itchy skin reactions, for example. The hair lies in thick pads on the back of the abdomen. The upholstery is also known as a mirror, which is why the hair is also called mirror hair. The mirror hairs are hollow on the inside and break off quickly. The broken hair can be spread over long distances with the wind. Widths of up to 200 meters are possible. The mirror hair is provided with barbs and sharp break-off areas. You can dig into the skin in thin spots. The protein thaumetopoein is located in the cavities of the hair and can lead to reactions of the immune system in human skin. The reactions to the protein poison can be different. Local skin reactions such as itching or inflammation can occur. Anaphylactic shock is also possible as an allergic reaction. The local Skin reactions with itching can be up to 7 days last for. If mucous membranes are affected, symptoms such as eye infections can also occur. The caterpillars withdraw into their web nests during the day. There the mirror hairs are present in large numbers and can trigger allergic reactions even after years.

Oak processionary moth - damage to trees

When the population is high, the caterpillars can largely eat the leaf mass of a tree and cause damage to the infested oak. A one-time clearing of the tree is initially not tragic. When the caterpillars are gone, the affected oak will develop new shoots and leaves. However, the tree is more susceptible to secondary pathogens. The secondary pathogens include, for example, oak powdery mildew, frostworm or oak splendor beetle. The oak processionary moth is also known as a forest pest.

Oak processionary moth and web moth

The nests of the web moth can be confused with those of the oak processionary moth. But not all caterpillars that form nests on bushes or trees are dangerous for humans. The web moth is harmless to humans. It forms extensive nests in the months of May and June. The nests often take up the entire tree, which leads to a ghostly sight. The caterpillars of the Web moth look different than the caterpillars of the oak processionary moth. While the latter have long hair and a dark habit, the caterpillars of the spider moth are yellowish-white, have no hair, but black spots.

Oak processionary moth - Control and removal of caterpillars and nests

If you noticed an infestation in your area in the past year, contact the official advice centers at the district office in good time or commission a specialist company to carry out prophylactic control with suitable sprays before the stinging hair becomes a danger!


Infested oaks should be freed from caterpillars and nests. The danger to people, animals and trees is too great. The distance should only by qualified personnel be carried out, because some protective measures must be observed. The removal is mostly done by mechanical methods. The mechanical processes include, for example, suction or collection of moulting residues and web nests. The aspiration of the web nests is carried out in the event of severe infestation. The removal of nests, moults and caterpillars requires specific knowledge.

A special suction device, protective clothing and specialist knowledge are necessary in order to Oak processionary moth to be disposed of safely.