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Toxic Caterpillars Are Invading England. Here's What You Should Do If You Spot One

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Warnings are being issued about a species of toxic caterpillar that has been spotted across London and the southeast of England. 

They’re the young of the oak processionary moth, and each caterpillar is covered in more than 62,000 long, white, toxic hairs.

The hairs can trigger allergic reactions, and can spark problems such as asthma attacks, skin and eye irritation, vomiting, and at worst, anaphylactic shock and death. 

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Less serious reasons can include itching, rashes, and, less commonly, sore throats, according to the Forestry Commission, which oversees forests in England and Scotland. 

The caterpillars can release the hairs — which contain an irritating protein called thaumetopoein — as a self-defence mechanism, or they can be carried in the wind if a caterpillar has shed them. Even once they’ve been shed, the hair can remain “active” for up to five years. 

Luckily, with their hairy bodies, the caterpillars are fairly distinctive. 

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Other things to look out for are their nests, which are described by the Forestry Commission as “white, silken webbing nests,” and which tend to be built on the trunks or branches of oak trees. 

The caterpillars also tend to move around in noticeable processions — which is how they got their name — creating nose-to-tail chains when they move from tree to tree. 

If you see one, you definitely shouldn’t touch it, or allow your pets or children to touch it. Instead, what you should do is call the Forestry Commission and report the sighting to them. You can find contact details and information about how to report sightings here

If you spot a caterpillar nest you also shouldn’t touch that, as the nests are generally full of left-behind hairs. 

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The caterpillars have been spotted in Croydon, Twickenham, Epping Forest, Watford, Ealing, and several London suburbs, as well as Bracknell Forest, Slough, and Guildford, according to the Guardian

While there haven’t yet been any reports of serious illness as a result of the UK outbreak, one gardener described her “severe symptoms” to the BBC, after she came into contact with the caterpillars in an allotment. 

“My first symptom was a rash on my tummy,” said the unnamed gardener. “I was unaware of what it was at thought at first it was a heat rash.” 

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“During this time I had spells of feeling violently sick,” she continued. “I thought I might have shingles. The rash got worse and the left side of my face became covered in this sore irritating rash. My left eye became very sore and weepy.” 


What you should do, according to the Forestry Commission: 
  • Teach children not to touch or approach the nests or caterpillars
  • Train or restrain pets so they don’t touch them
  • Keep horses and livestock a safe distance from infested oak trees
  • See a pharmacist if you experience symptoms after suspected contact
  • If you think you or someone in your care has had a serious allergic reaction, call NHS111 or a doctor
  • Consult a vet if you think your pet or livestock has been seriously affected 
  • Call in a pest control expert to remove infestations in your own trees
  • Report any sightings to the Forestry Commission


The caterpillars were first spotted emerging from eggs in mid-April, and trees were treated from April 23. The Forestry Commission will be treating trees with biopesticides at more than 600 sites, according to the New York Times

“The treatment programme is expected to continue until late May or early June,” said a spokesperson from the Forestry Commission. “After that the caterpillars will be too large to be affected by our preferred treatment product.”

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As well as the risk they can pose to humans, the caterpillars can also cause damage to trees.

“Large populations can defoliate, or strip bare, large parts of oak trees, leaving them vulnerable to attack by other pests and diseases, and less able to withstand stresses such as drought and flood,” according to the Forestry Commission. “They all only feed on other trees if they run short of oak leaves to eat, and have been seen on hornbeam, hazel, beech, sweet chestnut, and birch trees.”

The caterpillar, which originally comes from southern Europe, was accidentally introduced to Britain in 2005 when oak trees were imported from Europe that contained their eggs. According to the Guardian, it has now become established as far north as the Netherlands and northern Germany.

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