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Brown tail moth is an insect native to the UK that has hairy black caterpillars. The hairs are urticating (have an irritant effect) and can cause irritation if they come in contact with human skin. Although they can be a health problem plant damage is also possible.
Brown tail moth adults are white with conspicuous brown hairs on the end of their abdomens. They have a wingspan of approximately 40mm.
They emerge in July and August and lay batches of 150-250 eggs covered with brown hairs on suitable hosts. These are mainly in the Rosaceae family and include hawthorn, blackthorn, plum, cherry, rose and blackberry.
The caterpillars hatch after about three weeks and begin grazing the foliage and producing webbing. Little damage occurs in late summer as the young caterpillars soon spin dense silk hibernacula in which they overwinter. These shelters are often in exposed places such as at shoot tips and so are easily seen in the winter, especially as they invariably retain some dead leaves long after the others have fallen.
The caterpillars begin feeding again in April and may cause extensive webbing and defoliation. They are up to 30mm long, blackish with a white band along the sides. The body is covered with brownish hairs and at the rear end of the body there are two raised reddish tubercles. The hairs readily break off and can cause an intense irritation and rash on the skin. In some areas this moth is abundant and can be a public health problem, as well as having a severe impact on the growth of trees and shrubs. Pupation takes place inside silk cocoons on the host plant during June and July.
This moth is found mostly in Southern England and Wales and in some coastal regions further north.
In autumn and winter the most obvious signs of the presence of this moth are the overwintering silk hibernacula which can often be readily seen in the winter host plants have lost their leaves. In spring and early summer webbing is more extensive and the black and red caterpillars can cause some defoliation.
There are other species of moth that can cause webbing on a range of trees however brown tail moth is the only species which is black with brown hairs and two reddish raised tubercles.
A related species the oak processionary moth has become established in parts of London and areas of surrounding counties. The caterpillars of this moth also have urticating hairs but it is only found on oak trees. If you find oak processionary moth this should be reported, further details can be found on the Forestry Commissions webpages.
Brown tail moth caterpillars and there larval nests should not be handled without protection due to the covering or irritant (urticating) hairs. For this reason some local councils will take action against this insect.
Although infestations can be alarming infested plants will usually survive with only minor checks in growth
Due to the gregarious nature of brown tail moth caterpillars it is sometimes possible to prune out infested shoots. The silk shelters in which they overwinter can be easy to spot after the leaves have fallen. Rubber gloves should be worn to avoid contact with the caterpillars’ irritating hairs.
Pesticides for gardeners (Adobe Acrobat pdf document outlining pesticides available to gardeners)
Box tree caterpillar Cotoneaster webber caterpillarsOak processionary mothProtect your garden RHS statement on pesticides in horticulture Small ermine moths
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