Londoners Beware: These Toxic Caterpillars Cause Rashes and Asthma

The caterpillars were accidentally introduced to Britain in 2005

Thaumetopoea_processionea OPM.JPG
Each caterpillar of the oak processionary moth have about 62,000 hairs that contain a protein called thaumetopoein, which causes rashes, asthma attacks and vomiting. Kleuske/Wikimedia Commons

Officials are warning Londoners of a toxic caterpillar that causes asthma attacks, nausea and rashes.

According to the British Forestry Commission, caterpillars of the oak processionary moth (OPM), which live in and feed on oak trees, have been seen emerging from eggs since mid-April.

Native to southern Europe, OPM was accidentally introduced to Britain in 2005. The caterpillars can be easily recognized because they move around in “nose-to-tail processions” in late spring and early summer and because of their “distinctive white, silken webbing nests” left on tree trunks and branches.

Mature caterpillars’ bodies are dark on top, pale on the sides and covered in hairs and orange spots, The New York Times’ Jeffery C. Mays reports.

And while they might look harmless, it’s the caterpillars’ thousands of hairs that are the problem. As the Associated Press reports, the hairs contain a protein called thaumetopoein, which is what causes rashes, sore throats, as well as eye and breathing problems. They can also cause general illness, including nausea, fever and malaise.

Each OPM has more than 62,000 hairs. And hairs that fall off or are left behind in webbing nests can still cause problems for up to five years.

How to identify Oak Processionary Moth in woodlands, parks and gardens

“At best, you can get contact dermatitis. At worst, you can die,” Jason J. Dombroskie, manager of the Cornell University Insect Collection, tells Mays. “You can go into anaphylactic shock and have your airways close up. The airborne hairs set up a whole different ball game.”

While the Forestry Commission has told locals not to touch the caterpillars, the organization says that they don’t expect them to come down from trees towards the ground or even be large enough to be seen by the public until at least mid-May.

Some trees have already been treated with a biopesticide, the organization writes on its website. Oak trees at more than 600 sites around London, many of which were infested with OPM for the last several years, will continue to be treated through June.

Unfortunately, it’s not just people that are susceptible to the toxic hairs. An infestation of these caterpillars can destroy oak trees and leave them vulnerable to pests, diseases, floods and droughts, the Forestry Commission says.

While the caterpillar isn’t found in the U.S., it theoretically could make its way via an infested nursery, Mays writes.

Several outlets report that there have been no reports of serious illness linked to the caterpillar so far. But one gardener tells BBC News that she became violently sick and developed a rash after clearing overgrown weeds beneath her oak tree.

"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,” she says. Her doctor confirmed it was a reaction to OPM.

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