Toxic Caterpillars Will Invade London This Spring

October 21, 2018

Invasive caterpillars carrying highly venomous hairs could soon be marching through London, threatening oak trees and humans.

The London Borough of Bexley issued a warning earlier this month asking residents to be on the lookout for oak marching moths (Thaumetopoea processionea) after their larvae were spotted coming out of eggs high in the trees.

The moths themselves are not the problem. Rather, it’s what came before them: the caterpillars.

The body of the Oak Parade Moth caterpillar is covered with more than 62,000 tiny white hairs that contain a protein called tametropine. If people come into contact with this protein, it can cause rashes, itchy skin, and in some cases, sore throats, itchy eyes and difficulty breathing. In some cases, it can even cause anaphylaxis, a life-threatening allergic reaction, according to the New York Times.

What’s more, the caterpillar’s hairs can remain toxic for up to five years, according to the Times. This means that contact with stray hairs, such as those found in their nests, should be avoided at all costs, the UK Forestry Commission warns. Even coming into contact with a single windblown hair of these caterpillars can lead to health problems.

However, London residents still have time to prepare for the arrival of the caterpillars. With the arrival of spring, these creepy crawlies will break free from their eggs high up in trees. According to the Forestry Commission, as the caterpillars grow, they begin to descend trees to nest and gnaw on leaves – and grow poisonous hairs. But the commission expects the bugs won’t start descending into trees until mid-May, thus making their way into human life. At that time, the caterpillars will be easiest to spot when they march in a “nose-to-tail” fashion, as their name (oak moths in motion) suggests.

Caterpillars can also threaten oaks, but not because of their poisonous hairs. For oaks, the caterpillars’ appetite is more worrisome. According to the Forestry Commission, they devour the leaves of trees, sometimes leaving them exposed and unable to withstand pests, disease and environmental stresses such as drought and flooding).

According to the commission, efforts are underway to kill the caterpillars with insecticides, once they emerge from their silky nests.

The advance of the caterpillars
Oak march moths are not native to the UK, they are an invasive species. According to the Forestry Commission, they first appeared 13 years ago and are likely to be eggs hidden in oak trees brought in from mainland Europe. Given that this southern European species has been climbing north through Germany and the Netherlands for the past 20 years, what are the chances that the moths could have made it much further and ended up in our American backyard?

“It’s relatively unlikely,” said Mark Wright, an entomology professor at the University of Hawaii at Manoa who studies invasive species.” It’s less likely than, say, a fruit pest or something else that could easily move around on something we transport around the world.”

A live oak tree, on the other hand, isn’t really something we move around the world, Wright told Live Science. but if the poisonous critters somehow worm their way into a transcontinental cargo, they’ll be the least conspicuous as eggs, he said. Once they become caterpillars, however, they gather and move around, making it unlikely that agencies such as the U.S. Department of Agriculture’s Animal and Plant Health Inspection Service would miss them, he added.

According to Wright, there are other noxious caterpillars in the U.S., some of which are invasive.” We have a huge invasive species problem in the U.S., usually because of tourists transshipping goods,” he said. While the chances of this particular species entering the U.S. are slim, “that’s not to say it shouldn’t be watched.”