As It Happens

Toxic caterpillars from mainland Europe descend on British capital

Before reaching adulthood, the oak processionary moth develops as a hairy caterpillar that can cause skin rashes and more severe allergic conditions in humans.

Officials in London warn of an influx of hairy caterpillars that can cause severe allergic reactions

Oak processionary moths have been in London in their caterpillar form. (U.K. Forestry Commission)
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When you hear about dangerous animals in their natural habitat, chances are Wild Kingdom springs to mind before United Kingdom.

But that may be changing, as the city of London is under siege by a foreign species of creepy crawlies. 

Oak processionary moths have been spotted in their caterpillar form in the British capital over the past few weeks — and the public have been warned to stay away.

James Mallet, an entomologist at Harvard University, told As It Happens host Carol Off about the phenomenon.

Here is part of that conversation. 

What dangers do these caterpillars pose to people?

The hairs can detach, and they can stick into you and cause allergies.

They'll cause some irritation even in somebody who isn't allergic.

But to people who are allergic, it can be quite severe, and in some cases you might get anaphylactic shock resulting, which can lead to death.

So these caterpillars could actually kill people?

True, but that's true of a lot of other things as well that cause allergies in people.

Oak processionary caterpillars are seen in a nest on an oak tree in Zoetermeer, The Netherlands, in 2011. (Lex Van Lieshout/AFP/Getty Images)

Has there been a death from the hairs of these caterpillars?

I don't think in England. Somebody on the Internet had a picture of their dog that had very severe wheels on his nose.

In Europe is where you'd see that — these are European moths that seem to have been moved to the London area, centred in the Richmond area, and they're spreading out from there now.

Do you have to have contact with them, or is it airborne in any way?

If you brush against them, you may get the hairs. But they are also reported to be airborne. And people who live near trees may experience allergies, including respiratory allergies. The hairs do blow about. 

They crawl up the tree in a sort of procession, with everybody pressed with their head against the previous one's butt, to be technical. And for that reason they're called 'processionary'.- James Mallet, entomologist 

And they have quite a number of these hairs?

Something like 65,000 hairs.

They're called the oak processionary moth, which is a very regal sounding name. Why that name?

They're unusual in that they follow each other nose-to-tail.

They come down and rest on the ground or on tree trunks, and then they crawl up the tree in a sort of procession, with everybody pressed with their head against the previous one's butt, to be technical. And for that reason they're called "processionary".

It's called the oak processionary moth because they live on oak trees.

James Mallet, an entomologist at Harvard University, says the toxic caterpillar scare on London has been blown out of proportion. (Submitted by James Mallet)

It's an invasive species in the U.K., is that right?

Yeah, it's thought to have been transferred from Europe by somebody moving some tree seedlings or something like that.

They pretty much only feed on oaks — they will feed on other species of trees, but I don't think they'll affect that many trees in very urban areas.

My guess is that this danger is somewhat overblown. It's a typical British news story.

So what advice are authorities giving for how people should treat these creatures or avoid them?

The Forestry Commission would like to get rid of them — they're a forest pest. So they're advising people to call the Forestry Commission if they see an infestation, and they will come and try and destroy them or contain them in some way.

It may be be that there's a bit of global warming is involved, so that all of a sudden the normally cold and rainy shores of Great Britain are becoming more favourable for this particular moth.

What about in North America — Canada or the United States? Any sightings of the oak processionary moth over here?

I'm not an expert, but as far as I know, not. But you've got some nasty species — some of which are related — that can also cause rashes or more severe [conditions].

Like what, for instance?

The tiger moths, woollybear-type caterpillars. Usually hairy caterpillars are a problem. I've personally got rashes from spiky caterpillars as well.

Written by Kevin Ball. Interview produced by Mary Newman and Julian Uzielli. Q&A edited for length and clarity. 

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