The caterpillars emerge in spring and begin to eat the buds and leaves of many species of tree and shrub, in severe cases causing total defoliation before they move to other plants to continue feeding.

The caterpillars carry up to two million spiked and barbed hairs, which can penetrate skins, causing an irritant reaction. For asthmatics and hay fever sufferers, it is important that the hairs are not inhaled as these may cause breathing difficulties.

A good time to note if the caterpillars are present is in the winter after leaf fall. It may be noticed that silken tents are attached to small branches in the crown of your tree and in which up to 2000 caterpillars may be sheltering. It is at this time that prunings out the tents and burning them can be the safest and most effective form of control.

From spring the caterpillars become active and may be seen on the branches of trees and shrubs. These are between 7mm and 38mm in length (depending on age) and are dark brown in colour with a distinct white line down each side. The whole body is covered in tufts of brown hairs and two distinct orange/ red dots are noticeable on the caterpillars back towards the tail.

• Great care should be taken to avoid touching the caterpillars. In cases of large infestations, it would be wise to keep the windows closed to prevent them entering into your house.
• The only certain way of eliminating any infestation is by pruning out and burning the tents during the autumn/ winter period when the caterpillars are sheltered within.
• During the summer months when they are most active, contact chemical sprays may give some immediate control, but as only 10% of the caterpillars leave the tents at most times, it is not effective overall.

Yes, but there is a risk of doing so and precautions that must be taken. Many of the irritant hairs from the caterpillars are bound up in the tents and can become detached when they are pruned out.

More guidance on pruning out winter tents (PDF 37KB)

You are strongly advised not to attempt to deal with an infestation if you;

• are asthmatic
• suffer from hayfever
• have sensitive skin
• suffer from eczema
• do not have adequate protective clothing
• are not comfortable working at heights.

Avoidance is far better than cure and following recommendations will help to ensure that you are not affected. If you are unfortunate enough to be affected, you can expect a rash together with irritation similar to a severe nettle rash. Normally this will give a few hours of localised discomfort, and a warm bath and application of calamine lotion or antihistamine creams may ease the itching.

If any other symptoms are experienced or the irritation persists, medical advice should be sought without delay.