Oak Processionary Moth (Thaumetopoea processionea)

Oak Processionary Moth (Thaumetopoea processionea) by Trevor Morgan

The Oak Processionary Moth has established itself in London the South East of England since 2005. It was introduced by imported oak trees from Southern Europe.  The moth is a danger to its plant hosts. The caterpillars can strip the leaves off an oak to endanger the life of the tree. The caterpillars also represent a threat to humans, our pets and livestock. The caterpillars also represent a threat to wild mammals.

They are not common in the London area, but they have established colonies in Bromley in the near past and they are present in Bexley and west London now. High Elms park is on high alert; and there are plenty of oak trees in Darrick wood, so our park is vulnerable to infestation. If you have oak trees in or near your garden they are vulnerable too.  The adult moth can easily spread their dangerous caterpillars. Please be on the alert.

The caterpillars hatch out from eggs in March and April. They then make a nest of fine silk on either the trunk or branch of an oak tree. During the late spring and summer, the caterpillars leave their nests to head out into the foliage at dawn and dusk to feed on leaves. They move around nose to tail in a procession, hence their name. The procession leaves a silken thread behind which wends its way up the trunk of the tree and across branches.

It is relatively easy to identify the caterpillars which break out of, and return to, their nests made of fine silk webbing. The dark hairy caterpillars are about 25 mm long and it is the hair or bristles which produce inflammatory toxins (thaumetopoein and closely related compounds). which can damage your skin, lips and lungs.

https://www.royalparks.org.uk/parks/richmond-park/visitor-information/oak-processionary-moth

https://www.rhs.org.uk/advice/profile?PID=902

Apart from the damage to oak trees, the caterpillars and their nests represent a threat to public health and to the health of both domesticated and wild animals. So, it is important that you and your children and pets do not touch or even go near the caterpillars.

In the UK there are few natural predators of the moths such as the praying mantis. So, where there are infestations they must be cleared away by manual intervention using pesticides. If you see this moth’s nest or caterpillars report it to the Forestry Commission.

https://www.forestry.gov.uk/opm

 

You are best advised to not to tackle the caterpillars or nests yourself. The hairs of the caterpillar can blow around in the air. The nests and caterpillars need to be eliminated by professionals wearing protective clothing.

The symptoms vary from person to person. Some people do not respond to a mild exposure to the hairs but others, who are more sensitive, may develop a skin rash. It is almost certain that everyone will be affected by direct contact with the caterpillars to produce a skin rash or even cause asthma if the hairs are breathed in. The toxin can also cause inflammation to the lips, throat and eyes. In rare cases, the symptoms can be so severe that urgent medical attention is required. The toxin is even light sensitive and skin rashes can recur after the initial symptoms have disappeared. Mild rashes can be treated with ant-histamine cream.

 

It is difficult if not impossible to remove all the hairs and bristles of the moth by washing affected cloths which cannot be used again and are best incinerated.

Dogs and cats and livestock can develop similar symptoms to human beings but of course they cannot tell you where they have been to help identify a cause. It would be far better if we could rid ourselves of the moths altogether.

In southern Europe there is a similar species, the Pine Processionary Moth – (Thaumetopoea pityocampa). This moth makes similar nests and the caterpillars look the same and produce the same toxins. My wife and I came across their nests whilst walking in a pine forest near Bordeaux, curiosity did not get the better of us and we instinctively kept away from them. It was only researching this article that alerted me to what had seen. The nests were in trees all around us. The Pine Processionary Moth has not reached the UK yet and let’s hope that it never does to add to the problem.