Oak Processionary Moth Tree Surveys & Reports

Oak Processionary Moth Survey & Reporting

tree pruning services by peter yeates arboriculture

What is the Oak processionary moth?

The Oak processionary moth (Thaumetopoea processionea) is a fairly large moth with an average wingspan of 3.5cm in adult form while the caterpillars are up to 30mm in length. Adult moths are brown with a faint mottled appearance.

They are most active at night and are most commonly found in groups of up to thirty on the trunk and branches of the host plant. The caterpillars feed by spraying a corrosive solution from the tips of the setae (bristles).

It has a very distinct, at times alarming appearance. Its caterpillars are also quite distinctive and are covered in hairs that contain thaumetopoea, a toxin that can cause symptoms that range from mild itching to, in extreme cases, anaphylactic shock, which in some cases has proven fatal.

The moth is a native of the Mediterranean region and parts of Asia, but has been found in Britain, continental Europe, and Australia.

The Oak processionary moth, also known as the Oak processionary caterpillar, is a distinctive moth found in the UK, that causes skin irritation. The Oak processionary moth caterpillars can, when disturbed, inflict painful stings and severe blistering upon contact with human skin. They feed on oak trees, and all stages of the Oak processionary moth life cycle can be found on the trees. The moths life cycle is two years long, and the Oak processionary moths will congregate around oak trees during the winter.

is an invasive moth that has recently found its way into the UK. It is native to southern Europe, mainly southern France and Italy, but has spread to a number of other European countries. It is the larva that is the main problem, as they are highly destructive to oak trees.

Oak Processionary Moth Surveys & Statistics

Oak Processionary Moth Surveys

In the UK, oak processionary moths (OPM), the larvae of a small moth, are the most serious problem facing the trees. These caterpillar grow from 1cm to almost 5cm in the space of just a few weeks. They are most commonly found in the middle of the summer when they are in their final stage. They are easily recognised by a black tail with a white stripe.

The Oak Processionary Moth is only the second species in the UK to be classed as a Notifiable Pest in the UK (the first to be a native species).   It sits in the same category as the Emerald Ash Borer beetle, which has caused so much damage to ash trees in the UK.

Entomologists have already assessed over 280 sites in the UK for OPM infestation. Of these, 56% were found to be infested.

The moth defoliates the trees and can kill them by means of a disease it carries called "oak wilt" (also caused by the OPM). The moth is named for its habit of traveling in processions of hundreds or even thousands of moths, which it is able to do by producing a smelly, repellent trail that other moths can follow.

In the UK, the Oak Processionary Moth is a major concern for arboriculturalists due to its destructive feeding habits. (The moth prefers to live in older, neglected Oak trees, but it will also feed on the living bark of other trees, including other Oak varieties).

Are Oak Processionary Moths A Threat To Oak Trees?


If you are concerned about the health of your oak trees, there are a number of different health indicators used to diagnose their condition. As oaks are an important habitat for many species of wildlife, it is important that they are protected.  Oak trees are economically beneficial too as they support tourism, and the timber industry.

The oak processionary caterpillar (OPC) is a hairy caterpillar that feeds mainly on oak trees, such as the sessile oak (Quercus petraea) and the pedunculate oak (Quercus robur), but is found on a wide variety of deciduous trees including willow, birch, alder, beech, elm, apple, and pear.

If you have an Oak tree in your garden, or you work in domestic horticulture, you may have heard of the Oak Processionary Moth. It may also surprise you to know that you are likely to have one in your area. Another is the Ash Dieback which is a big problem in the UK. This moth is the most serious threat to the British Oak tree and if left to its own devices, could cause the demise of the iconic oak tree.

Are Oak Processionary Moths A Threat To People & Animals?

Are Oak Processionary Moths A Threat?

In a paper published in 2003, the oak processionary was named as the cause of an epidemic airborne disease because its hairs contain urticant chemicals that cause a violent skin reaction that lasts for a few days. The hairs that fall from the oak processionary caterpillars when they are molting are also irritating to the eyes and mucous membranes, and can cause conjunctivitis if they get in the eyes. The rash caused by the hairs is more severe on sensitive skin, such as children's skin, and in those who suffer from asthma, eczema or hay fever.

The Oak Processionary Moth is one of the most dangerous garden pests in the UK and one of its main characteristics is the irritating hairs that cover its body and legs.  If the hairs get on your skin, clothes, or even in your mouth, you will experience a swelling, red rash that can burn and cause itching for days afterwards.

The oak processionary caterpillar as the cause of an epidemic airborne disease due to the toxic reaction of its hairs which those who came into contact with it experienced a range of symptoms such as skin irritation, respiratory problems and asthma attacks. The hairs of the oak processionary caterpillar contain toxic chemicals and when airborne can cause irritation to the skin and eyes, coughing and wheezing.

The hairs are flaked off the caterpillar and float in the air like particles of dandruff. These hairs get into the air and are breathed in, causing a painful reaction in people with sensitive skin.

They can also leave milky poison droppings over their food source which can  cause a skin  irritant if they are touched.

Surveying for egg masses

January is the traditional time of year to start surveying for the Oak Processionary, the insect that can cause such destruction to our native oak trees in the UK and Ireland. Understanding exactly where and when the moths emerge and start to fly is essential to starting the survey at the right time.

Surveying for caterpillars


Given the problems that the Oak processionary moth can cause, you would think that it would be straightforward to survey for oak processionary moth in the UK, however, it is a tricky beast to identify and its life cycle is very different from other tree pests.  The Oak Processionary Moth is an invasive species and with our mild winters, the moth can now overwinter in the UK meaning that it is a pest year round.

Control of young larvae

These thin, elongated larvae are often found on oak trees in spring and early summer. Yellow and brown stripes on the body help to identify them. It is important to identify the larvae in order to ensure that they are not confused with other species which are harmless.  The larvae have a characteristic processional habit of moving in single file along branches and twigs.  Their habit of 'boiling' off tree trunks and branches to move upwards en-mass form large processions known as caterpillar storms.

Surveying for new nests and trails

A tree survey is a tree inspection - not a diagnosis. It is not a medical examination, and does not have the same connotations as such. It is an entirely objective view of the condition of an oak tree. The purpose of a tree survey is to provide information about a tree and its condition for a tree surgeon or arborist to use in forming an opinion about the condition of the tree, as well as to determine the potential causes of a problem.

Our local Oak trees have been around for many years, and as such are at risk of infestation by Oak Processionary Moth  (OPM). This is a problem not just for the oaks themselves, but also for us humans as we are at risk of being injured when the moth flight occurs.

Oak Processionary Moth (OPM), is a major threat to the UK’s native oak trees.  They have a voracious appetite and can consume entire branches, as well as leaving the trees themselves vulnerable to fungal infections.  Trees that are attacked by OPM are often left with unsightly scars; not only that, but they are also more susceptible to future attacks by OPM and other parasites.

Oak trees are a beautiful sight to behold and they stand tall producing oxygen and providing a habitat for birds and other animals, but they also provide a home and food for other creatures.

Oak Processionary Moth is a caterpillar that lives in acorns and oak leaves. These caterpillars are what we survey and remove at a property to ensure that they do not eat the host tree and cause damage to the tree.

This is one of the most destructive pests to attack our precious Oak trees.

Our surveyors are fully trained to survey around your trees safely, with the latest techniques. We can also give you the best solutions for protecting your trees.  If you would like to know more, then please contact us for more information.

Our Location & Coverage


Why Use Peter Yeates Oak Tree Surveys:

Fully Qualified Arboriculturists with full public and employers liability insurance to £10m.

When you hire Peter Yeates Arboriculture, you are also getting the expertise of Peter Yeates, who specialises in tree surgery & arboriculture, including oak tree reports.

He has been in the tree care field for over ten years and has been working with oak trees for most of his life, so he has a lot of knowledge to share.

Peter Yeates Arb offers tree surveying throughout Hampshire, including Winchester & Southampton.

We have been in business for over ten years, and have thousands of satisfied customers.

We take pride in our work, and know that a happy customer is the best form of advertising, so we aim to exceed our customers' expectations.

Our expert staff are highly trained to use a variety of equipment, which allows us to provide a fast and efficient service.

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Oak Processionary Moth & Oak Survey FAQs

Are oak processionary moths dangerous?

Oak processionary moths are a non-native species of moth that are becoming increasingly common in the UK. The caterpillars of these moths are covered in a very irritating urushiol. This urushiol is present on most of the body of the moths which means that they release it when they are touched or come into contact with clothing or skin. The urushiol is a potent toxin that can cause an allergic reaction in many people. The most common effect of the allergic reaction to urushiol is an itchy rash. The rashes that are caused by urushiol are very itchy and often result in pustules and blistering.

How can you tell an Oak processionary moth?

The oak processionary moth has a wingspan of around 20–25 mm (3/4 to 1 in) and as it approaches its final instar nymphal stage, its colour changes to predominantly grey with a red-brown head and prolegs.

How long does oak processionary moth live?

3-4 days

Where do oak processionary moths come from?

Southern Europe. Oak processionary moths are not native to the UK and their origin and migration pattern is not fully understood.

What do oak worms turn into?

Oak Processionary Moths

What does the processionary moth look like?

The adult moth is a medium sized moth, with a wingspan of 45-50 mm. The fore wings are brown with a white central stripe, consisting of a broad band running through the middle, and a narrower lunule on either side. The hind wings are greyish brown in color.

How do I get rid of oak worms?

If you've spotted any of the oak processionary moth caterpillars in your garden, it's time to get them under control. Contact us for professional advice.

How do you kill a processionary caterpillar?

We get asked frequently about how to kill a processionary caterpillar. It is a little more complicated than a simple pesticide application. The treatment for processionary caterpillars must be persistent and preventative in order to completely get rid of them. Specific treatments are required to kill the caterpillars while not harming other animals or plants in the process.

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