Infestation of Brown-tail moths on Spurn

Recent visitors to Spurn will have no doubt seen the warning notices put up by the Yorkshire Wildlife Trust warning them of the presence of the Brown-tail moth caterpillars which this year are infesting Spurn peninsula especially south of the narrows. Indeed no visitor can have failed to notice the thousands of marauding caterpillars marching here and there, along paths, on the road, on stiles and fences, and even on the beach, in their desperate quest to find food. Prominent, too, on almost every branch of every sea-buckthorn bush are the characteristic silken webs or tents formed by the caterpillars for their protection, and in which they have over-wintered. The first major infestation of this moth on Spurn occurred only last year when several thousand webs were present but their numbers, though unprecedented, have been totally eclipsed by the tens of thousands which now infest the peninsula.

Brown-tail larvae in web
Brown-tail larvae in web (Photograph P.A. Crowther)

The Brown-tail moth (scientific name — Euproctis chrysorrhoea) is a member of the Lymantriidae family of Tussock moths. The adult imago is a silky white colour except for the tip of the abdomen, which is a deep chocolate brown. The flight period of the moth is from approximately July to August but sometimes there is a small partial second generation around mid-October. The caterpillars are hatched from about August and overwinter as very small larvae in the protected webs that they have spun, and in early spring they begin to feed on the new growth of a wide variety of foodplants until they are fully grown around the end of May or early June when they pupate ready to emerge as adult moths in July.

Brown-tail larva
Brown-tail larva (Photograph P. Martin)

The species is well established in the south of England and further down the east coast from Hampshire to Suffolk and in the Thames valley but although it has occurred sporadically further north it is only in the last few years that it has occurred regularly further north a s far as Yorkshire and become sufficiently numerous to establish resident colonies. It was first recorded at Spurn in 1973 with just three individuals and not again until 1980 and then only in occasional years in single figures for the next two decades. It was thought that all these moths were immigrants from the continent and there was no evidence of breeding. It was not until the present millennium that Brown-tails were recorded in double figures, and 2004 when they reached treble figures and established themselves as a breeding colony. The rest, as they say, is history!

Adult Brown-tail moth
Adult Brown-tail moth (Photograph P.A. Crowther)

The Brown-tail moth is a pest species, not only because in large numbers it can strip trees and shrubs of their foliage (as it has done this year to the sea-buckthorn on Spurn) but also because the barbed hairs of the larvae break off and cause a painful irritation when they come in contact with the skin. People vary in their reaction to the larval hairs but those who are particularly sensitive can suffer a type of asthmatic reaction so should be careful to avoid all contact with the caterpillars. Indeed it is best to avoid contact with any stage of the moth, whether the larva, pupa, or adult insect. Minor skin irritations should be washed immediately or as soon as possible with hot soapy water and treated with calamine lotion applied as necessary. Serious or persistent symptoms, for example hairs penetrating the eyes or inhaled require medical treatment, but prevention by avoidance of close contact is the best course of action for everyone.

Brown-tail larva inspecting warning notice
Brown-tail larva inspecting warning notice (Photograph P.A. Crowther)

There is very little that can be done in practice to deal with a major infestation such as the one currently affecting Spurn this year because of the sheer numbers of caterpillars and webs involved. Treatment consists of snipping off each individual web or tent and removing it for subsequent burning. While this may be a practical solution where only hundreds of webs are involved it would take a whole army of trained operatives in protective clothing to deal with the literally tens of thousands of webs which are currently infesting Spurn peninsula. The only real hope is that nature herself will restore the balance as happened here with the recent population explosions of Garden Tiger moths and earlier to the Holly Blue butterfly. Many moth species have their own particular parasite which acts as a check on their population — usually one of the ichneumon or tachinid flies. It may be that the Brown-tail’s sudden incursion here has outstripped the parasite which would normally keep its numbers in control but only time will tell.

Note: the opinions expressed here are those of the author and not SKEALS

P. A. Crowther (May 2007)