Box tree caterpillars are the larvae of a moth that feeds on box (Buxus) plants. It is native to East Asia and became established in Europe in 2007. Although the first adult moth arrived in Britain in 2007, followed by several moths to light traps in 2008, caterpillars were not found in private gardens until 2011 in the home counties. By the end of 2014 the moth had become established in parts of London and surrounding areas. For growers in the south-east of England, it is now a problem that is likely to ​reoccur repeatedly throughout the

The period of time when an individual plant is in active growth. This will depend on the local climate and light levels, and can vary between different plants, although it is broadly from spring to autumn.

Defoliation caused by box tree caterpillar

Gardeners are likely to become aware of box tree caterpillar when they notice defoliation or find webbing and caterpillars on box plants.

• The caterpillars eat box leaves and produce webbing over their feeding area. Plants may also show patches of dieback, which can be especially apparent on trimmed plants. This is not to be confused with the dieback caused by the disease known as box blight
• Newly hatched caterpillars are greenish-yellow, with black heads. Older caterpillars reach up to 4cm (1¼in) in length and have a greenish/yellow body with thick black and thin white stripes along the length of the body
• Caterpillars are also capable of stripping bark, which can result in girdling of affected sections
• The pupae are concealed in a cocoon of white webbing spun among leaves and twigs
• The adult moth usually has white wings with a faintly iridescent brown border, although the wings can be completely brown or clear. The moth has a wingspan of around 4cm (1¼in)
• The pale yellow, flattish eggs are laid sheet-like, overlapping each other, on box leaves. These are very difficult to find

Check box plants frequently from early spring onwards so action can be taken before a damaging population has developed. When choosing control options you can minimise harm to non-target animals by using the methods in the non-pesticide section below. Pesticide treatments are likely to kill natural enemies and are only likely to be successful if the entire plant can be reached.
 

Non-pesticide

• Where practical, caterpillars should be removed by hand
• Pheromone traps, can indicate whether there are moths in the area and their level of activity. These are available from several suppliers including Agralan, Dragonfli and Solabiol
• The mixed nematode biological control sold as Fruit and Vegetable Protection has some effect on the caterpillars
• The caterpillars have a range of natural enemies, including parasitoid flies, parasitoid wasps, social wasps, spiders and ants
• There have been reports of garden birds including blackbirds, starlings, magpies and tits feeding on the caterpillars in some locations. It is not yet clear if this predation will result in a reduction of box tree moth numbers
• Consider choosing alternatives to box plants (see below)

Pesticides

The RHS recommends that you don't use pesticides. Most pesticides (including organic types) reduce biodiversity, including natural enemies, impact soil health and have wider adverse environmental effects.

• Extensive populations can be treated with an insecticide. Thorough spray coverage is required if control is to be achieved
• Forceful spraying is needed to penetrate into the interior of box plants through the webbed-together leaves
• Organic contact insecticides containing natural pyrethrins include Bug Clear Ultra 2, Neudorff Bug Free Bug and Larvae Killer. Several applications of these short persistence products may be necessary to give good control
• Further information about the use of pesticides available for management of box tree caterpillar is available on the pesticides for gardeners leaflet 
   

• Pesticides available to gardeners (Adobe Acrobat pdf document)
• Biological control suppliers (Adobe Acrobat pdf document)

Have you seen box tree moth? We would like to know.

As part of our research, the RHS would like to know where box tree moth has been seen. Please submit your records via our box tree moth survey (expected time to complete survey = two minutes).

Between 2015 and 2016, over 800 records of the moth were received. This jumped to over 3000 in 2017 and since 2018 have remained at more than 5 000 a year. The box tree moth is now considered to be a “common resident”, being widely distributed across England, particularly the south-east. It is also present in Wales, Scotland, Ireland and Northern Ireland.

Thank you to everyone who has submitted records so far.

• Watch an animated map of the results from the box tree caterpillar survey (links to YouTube)
• See all sightings you can submit to help our research

If you are looking for an alternative to box then there are plenty of shrubs that lend themselves similarly well to clipping.

Where it has become impractical to control box tree caterpillar, consider using a different hedge or topiary plant. Read our guide to choosing box alternatives, and then browse our box alternatives selection page to find a plant that works for you.

Read more about our ongoing Box alternatives trial where a range of compact evergreen shrubs are being grown at RHS Garden Wisley. The trial is situated in the Walled Garden at the end of the Jellicoe Canal in front of The Old Laboratory building. No box alternative has all the attributes of box, however, several of the shrubs are promising options; there are alternatives with small leaves that can be clipped into formal hedging styles.