Box tree caterpillar
Increasingly common in gardens, box caterpillar can completely defoliate box plants. Though relatively new to Britain, it has spread widely across England – particularly London and surrounding areas – and has reached the rest of the UK and Ireland.
Scientific name Cydalima perspectalis
Plants affected Box (Buxus)
Main symptoms Foliage is eaten and leaves webbed together
Most active April-October
What is box tree caterpillar?
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
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.
- 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)
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.We advising managing box tree caterpillar using the information above as your first course of action.
Pesticide treatments are likely to kill natural enemies and so reduce the likelihood of natural control and can lead to resurgence of the target animal.
The shorter persistence products (that are usually certified for organic growing) are likely to be less damaging to non-target wildlife.
The pesticides listed are legally available in the UK. This information is provided to avoid misuse of legal products and the use of unauthorised and untested products, which potentially has more serious consequences for the environment and wildlife than when products are used legally.
Always follow the instructions on the products.
Homemade products are not recommended as they are unregulated and usually untested.
Be aware that products such as Xentari are not registered for use in the UK and we cannot advise on their use.
Plants in flower should not be sprayed due to the danger to pollinating insects.
- 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
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).
Privacy notice: Submissions to our surveys are stored permanently in an anonymised form in order to monitor the spread of the insect or disease. We may contact you within 2 months of your submission in order to verify your sighting but your personal data will not be permanently stored in connection with your submission and will be deleted after 1 year. We publish and share only non-identifiable data from survey submissions (such as a six figure grid reference) with third parties and the public for the purposes of scientific research and advancing understanding among gardeners.
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.
Choose alternatives to box
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.
Box tree moth overwinters as small caterpillars, hidden between box leaves that have been webbed together in late autumn. These caterpillars begin to become active as the weather warms in the spring – they have been observed feeding as early as February on particularly warm days. By June, caterpillars will have finished feeding, pupated and emerged as adult moths.
There is then a second emergence of adults in late July/early August as the next generation of box tree moths emerge, looking for mates. During summer overlapping of generations has been observed, with multiple life stages of the moth present at the same time. However, by late September/October the majority of the population are early instar caterpillars.
The adult moths are good flyers and are attracted to light.
The first occurrance of larvae of the box tree moth Cydalima perspectalis (Lepidoptera: Crambidae) in private gardens in the UK (Adobe Acrobat pdf document)
The box-tree moth Cydalima perspectalis (Walker, 1859) in Britain: an overview of its spread and current status (Adobe Acrobat pdf document)
First records of two natural enemies of box tree moth, Cydalima perspectalis (Lepidoptera: Crambidae), in Britain (Adobe Acrobat pdf document)
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