The caterpillars of the oak processionary moth actually seem quite harmless. But the impression is very deceptive: Not only can the animals' poisonous stinging hairs cause a severe allergic reaction in humans and animals, the caterpillars are threatening oaks and other trees due to their large-scale appearance in recent years.
Why is the oak processionary moth so dangerous to humans?
Oak processionary moths can cause severe rashes in humans. It's not just villagers whose houses are near forests who are particularly affected. Other groups of people and people who frequently spend time in certain places are also at risk:
| Affected locations and areas | Affected groups of people |
|---|---|
| Kindergartens, schools and playgrounds | Children and adults in appropriate facilities |
| Sports fields and other outdoor sports facilities, outdoor swimming pools, campsites | Those seeking relaxation, visitors to sports and other leisure facilities |
| Parks and other public green spaces, wooded cemeteries | Those seeking relaxation, walkers, hikers, residents |
| wooded recreational areas | Employees and workers in gardening and landscaping, from parks and cemetery authorities, road maintenance departments, forestry workers, construction workers, etc. |
| Roads, highways and rest stops, parking spaces (through street trees and avenues) | Car drivers, cyclists, pedestrians |
The following video explains and shows very well what the oak processionary moth's stinging hairs can do to humans:
Symptoms are similar to an allergy
The symptoms, which are quite similar to an allergic reaction, occur after contact with the caterpillar's poisonous stinging hairs. You don't even have to have touched the animal directly, because the easily broken hairs also float in the air - especially on windy days. The hairs contain a contact poison, which can lead to the following symptoms in humans and animals:
- severe itching
- red skin
- Formation of wheals, nodules and pus blisters
- Conjunctivitis when the hairs come into contact with the eyes
- Inflammation of the respiratory tract if the hairs were inhaled
In severe cases, acute shortness of breath can also occur, in which case you must definitely call an emergency doctor! If you come into contact with the oak processionary moth not just once but more often, a real allergy can develop.
The symptoms typically only appear a few hours after contact with the toxic hairs, so many people do not initially make a connection between their discomfort, the rash and yesterday's walk in the forest.
When do you have to go to the doctor?
You should definitely visit your family doctor or a dermatologist and have them prescribe antihistamines and anti-inflammatory creams to combat the often very severe itching. In the event of conjunctivitis and shortness of breath, further medication is necessary as quickly as possible to prevent worse consequences and inflammation.
Touched the caterpillar? This is what you have to do now
If you were traveling in a contaminated area or even touched a caterpillar or web, you can mitigate the bad consequences by taking the following measures:
- take off worn clothing and wash at 60 degrees Celsius
- take a shower immediately, lather and rinse skin and hair several times
- rinse your eyes, nose and mouth in particular with clean water
- Get advice from the pharmacy and get an antihistamine ointment as a precaution
Then you have to wait and see, because the first symptoms only appear after a few hours or even the next morning. In the event of a severe reaction, these can also be accompanied by fever, dizziness and fatigue.
Prevention and defense
Anyone who discovers an infestation of oak processionary moths should keep their distance if possible
Of course it is best if there is no close contact with the oak processionary moth and thus no he alth problems. How to prevent:
- Do not touch caterpillars and webs under any circumstances
- instead keep your distance and don't sit on the ground nearby
- If infested areas are known: do not enter them
- the fine hairs also fly around in the air
- When taking a walk in the forest, protect uncovered body parts (arms and legs, neck, neck) with suitable clothing
- Infested areas should only be entered if absolutely necessary and with full protective clothing (e.g. for professional reasons)
Oak processionary moth in the garden
If you have found the caterpillars and their web nest in your garden, under no circumstances should you remove them yourself! Instead, hire a pest controller or an experienced arborist. Do not spray the caterpillar nests with a jet of water or flame them: this will stir up the fine poisonous hairs and spread them around the area.
Fighting oak processionary moths
You should under no circumstances take on the fight against the oak processionary moth yourself, but rather leave it to the trained professionals. As a rule, these appear very quickly in populated areas, but in the forest, control measures are only necessary if there is a severe infestation.
Found caterpillars? You should report your find here
Due to the high level of he alth risk to humans, animals and nature, you are required to report if you have discovered oak processionary moths or a web nest. The municipalities are trying to kill the pest using methods such as vacuuming or burning or by applying insecticides, if possible before the third instar caterpillars develop. In the event of a discovery, you can contact the responsible he alth or public order office.
Many regions and cities in North Rhine-Westphalia are heavily infested with the oak processionary moth this year - including Münster. In the Hiltrup district, the caterpillars and webs were vacuumed up this morning. ??
A post shared by Wochenblatt.com (@wochenblatt_com) on Jun 12, 2019 at 6:55am PDT
Natural enemies
Fortunately, the oak processionary moth has many natural enemies that are immune to its poison and like to eat the caterpillars instead. Bird species such as the cuckoo and the strikingly colored oriole are included, as are these parasites and predatory beetles:
- Bugs
- Caterpillar flies
- Parasitic wasps
- Big and Little Doll Robber
However, the natural predators cannot fight the population alone if they occur in large numbers, especially since only a few bird species dare to attack the poisonous caterpillars. However, settling these animals in the garden helps to prevent or keep any infestation at bay.
Control methods
To combat the oak processionary moth, professionals use various methods, some of which are controversial, especially among environmental protection associations.
Mechanical and thermal
There are three different mechanical or thermal methods to combat the caterpillar, all of which are used from around the end of May:
| Procedure | Implementation | Pro | Contra |
|---|---|---|---|
| Suction | Suction of caterpillars, webs and their contents using special devices | residue-free, gentle on the surrounding nature | cumbersome, not very suitable for mass infestations |
| Burn down | Burning down the caterpillars and web nests using a gas burner | complete destruction of organic material | Churning up the poisonous hairs, damaging the tree, risk of fire |
| Collect | Gluing the web nests together with the caterpillars using suitable preparations and then removing them | residue-free, gentle on the surrounding nature | inconvenient, not very suitable for mass infestations, danger to those carrying out the work |
The resulting biological waste is considered corrosive operational waste and is completely disposed of in a special incineration plant.
Chemical and biological
Many municipalities combat the mass occurrence of the oak processionary moth by applying chemical pesticides or a spray mixture enriched with the bacterium Bacillus thuringiensis, which are sprayed using helicopters over large areas or on individual trees on the leaves of trees that are infested or threatened with infestation. These methods are effective, but also pose massive risks to the environment. Not only the caterpillars of the oak processionary moth, but also other butterfly caterpillars and breeding birds die from it - the latter not only because of the toxins, but above all because of the subsequent lack of food. Environmental associations therefore advocate more gentle methods such as suction.
Features
The oak processionary moth (lat. Thaumetopoea processionea) is a nocturnal butterfly from the tooth moth family (lat. Notodontidae). The adult butterfly is quite inconspicuous, but can be easily recognized by the following features:
| Body Feature/Gender | Male butterfly | Female butterfly |
|---|---|---|
| Wingspan | 25 to 32 mm | 30 to 36 mm |
| Coloring forewings | glossy ash to brown-gray with two dark, whitish-edged crossbands | darker colored than the male with little to no markings |
| Coloration of hindwings | yellowish-white with brownish arch line and dark spot, fringed | grey-white, fringed |
| Abdomen | gray-black hairy | gray-black hairy, blunt end |
| Special features | Wings can be very dark and without markings | Wings can be very dark and without markings |
The adults fly between the end of July and the end of August. The caterpillars, on the other hand, look quite different depending on the stage. They go through a total of six different stages before pupation, but right from the start they have long, poisonous hairs that break easily. The animals hatch between April and early May and migrate to the treetops every evening to feed at night. Entire processions up to ten meters long – hence the German name – can be formed with up to 30 animals next to each other.
Excursus
Danger of confusion with the harmless web moth
The white webs of the oak processionary moth, which are often found on tree trunks or in the forks of branches, are similar to the white nests of the various web moths. However, in contrast to the oak processionary moth, these are completely harmless. You can recognize a web moth nest by these features:
- Spreading: Web covers entire trees and bushes
- Preferred trees: bird cherries, willows, poplars, hawthorns, poplars, sometimes fruit trees
- Appearance of the caterpillars: yellowish with black dots, completely hairless
- Danger: infected trees sprout again in the same summer due to rapid pupation
The nests of the oak processionary moth, on the other hand, are locally limited to the trunk of the affected tree, and other tree species are usually affected than those of the web moths.
Distribution and habitat
Climate change is to blame for the massive proliferation of the oak processionary moth. Originally native to southern Europe, the dangerous caterpillars have now reached northern Germany.
The oak processionary moth is originally native to the Iberian Peninsula, i.e. in Spain and Portugal, from where it began its campaign of conquest across southern and central Europe to the south of Russia and even northern Europe several decades ago. Caterpillars and butterflies are now even native to northern Germany and southern Sweden.
In Germany, all federal states are affected, but wooded lowland regions in Berlin and Brandenburg, Baden-Württemberg, Bavaria, North Rhine-Westphalia and Saxony-Anh alt are particularly characterized by a mass occurrence. The animals prefer forests rich in oak, especially pine forests with oak trees and oak-hornbeam forests. But they also occur on individual trees, for example in parks, on roadsides or on avenue trees. The oak processionary moth prefers dry and sunny locations.
Biology and lifestyle
The inconspicuous, small butterfly mainly swarms between July and August, but can also appear in September. Then, within a few days, the females lay up to 300 eggs, preferably on branches in the crown area of the trees on the warm south side. The so-called egg caterpillar overwinters here, easily surviving frosts down to minus 29 degrees Celsius. The eggs, which are approximately one millimeter in size, are well camouflaged by a brownish glandular secretion.
Hatching period of the larvae
As soon as the oak leaves emerge in April and May of the following year and the spring is warm and dry, the caterpillars hatch. These are initially brown-yellow in color, but as development progresses, their color changes to gray-black. In total, the caterpillars of the oak processionary moth complete six different larval stages within the nine to twelve weeks until pupation.
Young caterpillars in the first and second instars do not yet have any dangerous stinging hairs, as these only develop in the third larval phase. From this point on, the caterpillars can be easily recognized by the long caterpillar hairs sticking out in bundles. However, these are non-toxic for humans and animals because the actually poisonous stinging hairs are very short and only 0.1 to 0.2 millimeters thin. They are only repelled when threatened. A single fully developed oak processionary moth caterpillar has up to half a million of these poisonous stinging hairs.
These caterpillars love it warm and dry! That's why the oak processionary moths are currently spreading along many forest edges, in gardens and parks in Germany. The hairy caterpillar actually looks quite funny. But their hair is a problem: it can be the cause of nasty itching, rashes or even coughing. So: Don't touch the funny animals and keep your distance. If you accidentally touch them: quickly take a shower and wash your hair and clothes! You can find out more about this on logo.de and in the logo! show - today at 7:25 p.m. with @go.to.joe ZDFlogo
A post shared by logo! (@zdflogo) on Jul 5, 2019 at 9:11am PDT
Nest building
Finally, in June, the caterpillars of the oak processionary moth build their typical web nests. These are mostly found on the trunks of oak trees, but sometimes also in the forks of branches. The animals need the nests for their molt. Over time, the caterpillar nests fill up more and more with old larval skins and feces and can eventually grow up to one and a half meters in size.
However, the caterpillars do not stay there permanently, but instead migrate in columns in several rows to the treetop in the evening and at night, where they feed all night long and finally return to their nests at sunrise.
Pupation
If the animals have eaten enough from the end of June / beginning of July, the pupation process begins. This also takes place in the web nests and lasts between 20 and 35 days. However, the poisonous stinging hairs of the caterpillars remain in the nests, which is why they can be dangerous for people and animals even after years without caterpillars.
Hatching time of the butterflies
The adult moths of the oak processionary moth finally hatch in mid-August. The differently colored male and female animals immediately begin their nuptial flight, at the end of which the females finally lay their eggs. The butterfly itself only has a very short life expectancy and dies in the fall.
Background
Warm and dry climate favors mass occurrence
The oak processionary moth needs a warm and dry climate to develop, which is why it appears in large numbers in years with corresponding springs and summers as well as after subsequent mild winters.
Oak trees dying due to mass caterpillar damage
Until about 30 years ago, the oak processionary moth only appeared sporadically in Germany, which is why feeding damage was only minor and the affected trees were also able to regenerate well thanks to their strong St. John's shoots. From the 1990s onwards, however, this changed, as the pest now appeared in large numbers in years with favorable climatic conditions.
A one-time denudation is actually not that dramatic for the trees in question, as they will sprout again. However, it becomes problematic if the oak processionary moth appears strongly for several years in a row. In this case, the trees' ability to regenerate suffers, they become weakened and susceptible to other pests and diseases such as the oak beetle or powdery mildew. As a result, the affected trees no longer grow or only show stunted growth, no longer produce acorns and ultimately die.
food plants
As its name suggests, the oak processionary moth feeds primarily on oak leaves. The pest can generally be found on all types of oak, regardless of whether it is a native sessile or pedunculate oak or the red oak from the USA. In exceptional cases, however, other deciduous trees and occasionally conifers (such as pines) are also attacked.
Frequently asked questions
Can the oak processionary moth also be dangerous to pets?
Dogs in particular are at risk from the caterpillars of the oak processionary moth, as the animals run through the bushes while running freely and come into direct contact with the poisonous hairs. Although the dog's body is largely protected by its fur, uncovered areas of skin such as the muzzle and the oral mucosa are at risk - the latter from licking itchy parts of the body. The same also applies to cats. Basically, the same symptoms can occur as in humans, and the treatment is the same: Wash your pet thoroughly (e.g. in the bathtub or with the garden hose, if necessary let it swim in a lake or stream) and find one Vet up.
There is a warning sign in our city park. Why should you avoid entering an area infested with caterpillars?
These warning signs identify areas contaminated with oak processionary moth caterpillars that should, if possible, not be entered. The reason lies in the animals' poisonous hairs, which can fly for kilometers through the air in windy weather and can therefore be inhaled.
Tip
Nematodes of the type Steinernema feltiae are also effective against the oak processionary moth as long as they are applied in favorable weather and during the second larval stage.
