Brown-tail (caterpillars) - Stuart Read

In recent years, and particularly in 2019, Brown-tail Moth caterpillars have been seen in huge numbers in our towns and cities, and across the countryside, in much of southern England and East Anglia.

We see the caterpillars in spring and they strip the leaves of trees and bushes and march off in search of something else to eat, and it is then that they come in contact with us humans. Each caterpillar bears a mass of tiny barbed hairs. The hairs get under our skin, literally, causing a nettle-like rash with it comes an irresistible urge to scratch.

So, what does the Brown-tail Moth look like?

The caterpillar lives with its fellows in a communal tent made of whitish silk, usually on the sunny side or at the tops of trees and bushes. When large, the caterpillars are dark brown with orangey brown hairs, with white tufts down their sides and two characteristic orange warts on the back. The adult moth is all white with a brown tuft of hairs at the end of the abdomen, hence the name.

Why the outbreaks now?

Brown-tail Moth populations explode occasionally, and have been doing so for hundreds of years. The first recorded outbreak was in 1720, near Kew outside London. Around 1900 the moth was so rare that some people thought it might disappear. These days outbreaks seem to be getting more frequent and the moth is spreading inland and northwards. We don’t know, but global heating may be partly to blame.

What should you do if you see the caterpillars?

Don’t panic. Leave them alone, don’t touch and try to stay away from areas where there are lots of them. The caterpillars are a problem in May and early June, much less so at other times. If they are in the house or on the garden furniture, put on vinyl gloves, pick them up and drop them in a bucket of soapy and salty water.

What should I do if I get the itchy rash?

If you get the rash, which is often on the hands, arms and neck, apply antihistamine cream or calamine lotion. Symptoms should subside after a few hours, but seek medical help if you are unsure, or the reaction doesn’t lessen.

Can we stop the outbreaks happening?

Not really, we’re going to have to learn to live with the increased frequency of outbreaks. But there are things we can do in the autumn and winter. The young caterpillars hatch from eggs in late summer, feed on leaves, and start making a small silk tent in which they spend the winter, exposed at the tops of trees and bushes. These tents are easy to spot when the leaves fall, and can be safely clipped off bushes and burned in a garden incinerator. Alternatively, if they are in areas you can’t reach, let your local authority know so they can hopefully map where outbreaks are happening and decide if action if needed. Identifying infestations during the winter and dealing with them before spring can be very effective. Once spring comes and caterpillars are on the march, it is nearly impossible to do anything about them.

Other caterpillars that make silk tents

There are other caterpillars that make silk tents in the spring but they look quite different to the Brown-tail Moth. Commonest is the Lackey, with its long, stripy blue-grey caterpillars, and much rare is Small Eggar with its jet black caterpillars sitting on a bright white nest. These species are comparatively harmless and just two of 2,500 species of moths that this in this country.