Oak processionary moth – what symptoms does the caterpillar trigger?

Oak processionary moth – what symptoms does the caterpillar trigger?

The oak processionary moth is a butterfly that has gained notoriety for being dangerous to humans. The caterpillars of the inconspicuous moth can trigger many symptoms, from slight reddening of the skin and a rash to allergic shock – and that just by touching their fine hairs. In this article, you will find out how to recognize them, how dangerous the animal can be and what to do in an emergency.

What is an oak processionary moth?

Oak processionary moths (Thaumetopoea procession) are moths, a subspecies of butterflies. The adult moths fly between July and September and are found throughout Germany. Their offspring, which will be the focus of this article, hatch from their eggs each season between early April and early May and then go through various stages of development, although they are still harmless in the early larval stage.

Between May and June, the caterpillars develop stinging hairs that can have various health-endangering effects on humans. Each caterpillar has around 700,000 hairs on its body.

In addition to the oak processionary moth, other processionary moths also occur in Europe, such as the pine processionary moth and the pine processionary moth. However, neither species occurs in Germany.


How do you recognize oak processionary moths?

Oak processionary moths are inconspicuous grey-brown and have a wingspan of up to three centimetres.

A dark back line and red-brown warts can recognize the moth’s caterpillars already mentioned. The long, white, stinging hairs, which can be responsible for health problems in people who come into contact with them, are also very distinctive. The animals often move in large groups, similar to a procession – hence the name.


The nests of the oak processionary moth are mainly in oaks, occasionally also in hornbeams or other trees. Dense white webs characterize them and can have different shapes, such as bag-like or blanket-like. They are also variable and can vary from coin-sized to meter-sized buildings. The distinctive nests are no longer accessible to recognize after a short time but still house the harmful white hairs. Old webs in oak trees can, therefore, also pose a danger.

The processionary moth is mainly found in oak-rich forests, rarely on individual trees in the city, for example, in parks or on the side of the road.

How do oak processionary moths harm humans?

The already mentioned stinging hairs of the larvae break off easily and can be carried away over long distances by air currents.

They then stick to trees, for example, or lie on the ground and thus come into contact with humans. This happens either by directly touching an area where the fine nettle hairs are located or by the hairs sticking to clothing and thus coming into contact with the skin.

The symptoms do not appear through stings or bites but through simple contact with the hair of the moth caterpillars. The trigger is thaumetopoein, a nettle poison in the stinging hairs.

The stinging hairs of the caterpillars cause health problems because they can easily penetrate the eyes, the upper layers of the skin and the upper respiratory tract via the mouth and nose. Various complaints can express the penetration of the hairs.


How long are oak processionary moth hairs dangerous?

The caterpillar hairs can remain in bushes for years, causing harm to humans. However, the danger is particularly acute between May and June when the caterpillars develop stinging hairsFrom the end of June to the beginning of July, pupation begins in the webs before the moths leave them. Between July and September, the stinging hairs can spread from the empty nests and thus continue to damage health. But even from old nests, the hair can cause problems all year round.

It is difficult to say when the danger posed by the oak processionary moth is over since even the hair of dead caterpillars can still trigger symptoms.

What are the symptoms?

The hair of the caterpillars can cause various ailments in humans, which can affect the skin, respiratory tract, eyes or other areas of the body. Below, we present the possible symptoms.

  1. Skin symptoms from direct contact with hair

The following signs can appear on the skin after contact with the oak processionary moth:

  • Skin rashes (caterpillar dermatitis) in the form of reddened skin similar to insect bites and slight swelling ( red bumps)
  • Itching and burning of the affected area
  • Pimple
  • Wheels, i.e. itchy swollen areas, possibly all over the body: Thin areas of skin are particularly affected, such as on the neck, face or the inside of the elbow


  1. Respiratory symptoms from inhaling hair

Respiratory symptoms include:

  • Irritations in the mouth and nose
  • Swelling and inflammation of the mucous membranes
  • Sore throat
  • painful cough
  • mucous sputum
  • Asthma attacks (in people who are prone to them)
  1. Symptoms caused by the penetration of the stinging hairs into the eyes

The following symptoms can occur in the eye area:

  • Conjunctivitis with pain and itching
  • Redness of the eyes and swelling of the eyelids
  • In rare cases, penetration is so deep that the hairs have to be surgically removed
  1. Other symptoms

Other symptoms can also occur:


How long does it take for the rash to go away?

The above skin irritations appear within eight hours of contact with the caterpillar hairs. It can take up to two weeks for the rash, known as caterpillar dermatitis, to disappear.

The other symptoms can also last several days to weeks if left untreated.

Is it possible to have an allergic reaction to caterpillar hair?

The typical skin rash that develops on contact with the hair of the caterpillar is believed by many to be an allergy but is a normal reaction to the venom. However, a few people also develop allergic reactions the second time they come into contact with the hairs of the caterpillars. This is not possible on the first contact since the body’s immune system must first have come into contact with the nettle toxin thaumetopoein contained in the stinging hairs before it can react to it with an allergy the next time.

The allergic reaction occurs quickly, within half an hour after contact. It can also manifest through reddening skin, wheals, itching and pain in the affected skin area. In addition, hay fever-like symptoms can occur, which can manifest themselves in severe sneezing and itching as well as burning and tearing of the eyes. General symptoms, such as those mentioned above, can also occur as part of the allergic reaction.

Very rarely, it can also lead to severe courses that can lead to cardiac arrhythmia or classic allergic shock. In addition to extensive skin reddening, this can lead to a massive drop in blood pressure in the affected person. The result is shortness of breath, dizziness, weakness, and an accelerated heartbeat.

Can you die from oak processionary moths?

Allergic shock, such as that caused by caterpillar hairs, can lead to death. If the above signs, i.e. a widespread skin rash with wheals and itching in combination with shortness of breath and dizziness, occur, medical help should be sought immediately.


What should you do after contact with oak processionary moths?

If you spot the hairs of the caterpillar on your clothing or have come into contact with them or a nest of the oak processionary moth, the following measures are recommended:

  1. Change worn clothes and shoes. Ensure you remove the clothing you have worn outside and not in the living area.
  2. Wash clothes at 60 °C.
  3.  Wash your body, including your hair, with soap . Avoid getting the shower water in your eyes.
  4. Do not scratch; this could allow the hairs to penetrate the deeper skin layers.
  5. If the eyes are affected, you should rinse them with water.
  6. Do not rub your eyes with your fingers.

What helps against the rash caused by oak processionary moths?

If the skin is already reddened, it is advisable to apply cooling compresses to the affected areas. This home remedy can reduce the itching and swelling that may occur.

Treatment with creams or ointments containing cortisone can also help to relieve the symptoms. Such creams, which contain hydrocortisone, for example, can be obtained from pharmacies without a prescription.

If the itching is severe, taking medicines that help against allergies, such as cetirizine or antihistamines, is advisable. This is also available in pharmacies without a prescription.

Breathing sprays are also used for asthma and are recommended for respiratory problems.

When should you seek medical help?

A visit to the family doctor is recommended if the symptoms, such as itching, are severely detrimental or if those affected suffer from breathing difficulties or severe swelling. With superficial redness and minor rashes, you can try to treat them yourself with the abovementioned remedies.


What to do against oak processionary moths?

Since the moths pose a health risk, they are controlled in some areas with the help of vacuum cleaners and insecticides.

To enable control in the first place, it is essential to report the sighting of the dangerous caterpillars of the moth or the nests in oaks and other trees to a responsible city or community office. The town hall, the regulatory office, the health department or the green space office are the main places to be considered.

There is no obligation to report this, but the authorities can counteract a massive infestation with the processionary moth and warn other area residents about the caterpillars. Residents can thus avoid the affected areas.

The sighting should be reported particularly urgently if the caterpillars were found in public places, such as playgrounds or parks. Under no circumstances should you try to remove a nest with the caterpillars of the oak processionary moth yourself – in the event of an infestation with the animals in your garden, leave the fight to professionals in the field of pest control.

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