Warning issued to homeowners as caterpillar destroys gardens

South Wales Guardian

17-07-2025

Homeowners are being urged to keep an eye on their gardens this summer as experts warn of an expected surge in damage caused by a fast-spreading invasive pest – the box tree moth caterpillar.
Ecology specialists at Arbtech have raised the alarm over the caterpillars as they are a species that's wreaking havoc on box hedging and topiary plants across the UK.
The caterpillars, which are the larvae of the box tree moth, feed on box leaves and bark, often leaving once-pristine shrubs brown, bare, and beyond saving in a matter of days.
This species of caterpillar can easily destroy plants (Image: Getty)
These caterpillars don't pose a direct threat to humans or pets, but they are said to be a nightmare for avid gardeners, especially those with ornamental hedges or neatly clipped box borders.
First spotted in the UK in 2007, box tree moths have spread rapidly, with sightings now common in gardens across southern and central England.
Numbers typically spike between April and October, with multiple generations hatching during the warmer months, leading to new waves of hungry caterpillars.
Activity is particularly high in July and August, and if left untreated, infestations can be devastating, with heavily infested plants often needing to be removed and replaced altogether.
An ecologist from Arbtech said: 'Box tree moth caterpillars might look harmless, but they're an invasive species that can strip a healthy plant in no time - and because they often feed from the inside out, many people don't realise there's a problem until it's too late.
'Box hedging is hugely popular in British gardens, so this species is having a serious impact not just aesthetically, but financially too.
'We're urging homeowners to check their plants regularly over the summer months. Look for tell-tale signs like webbing, leaf loss, or green-and-black striped caterpillars.'
Describing the caterpillars, the Royal Horticultural Society (RHS) said: '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.'
The team at Arbtech have shared some tips to help you prevent the box tree moth caterpillar from damaging your garden.
Look for chewed leaves, sudden browning or thinning patches in your plants as they could be caused by these caterpillars (Image: Getty)
Regular checks are the best way to catch an infestation early. Box tree caterpillars often start feeding from inside the plant, so damage might not be obvious straight away.
Look for chewed leaves, sudden browning or thinning patches. Webbing in the centre of the plant, often mistaken for spider silk, is a common sign.
You may also spot black pellets (droppings) around the base or within the foliage.
Box tree caterpillars are bright green with black heads and thick black and white stripes running down their bodies. Most are around 2-4cm long.
You'll often find them hidden deep inside the plant, especially on the underside of leaves or in sheltered spots. As numbers grow, they may spread outwards and become more visible.
If you spot one, it's likely there are more nearby. Catching them early is key to avoiding serious damage to your box plants.
For small infestations, you can remove caterpillars by hand - just make sure to wear gloves.
The earlier you treat the problem, the more likely you are to save the plant. Timing is crucial - aim to treat when the caterpillars are actively feeding, typically in late spring and again in late summer.
If you prune or remove an infested plant, dispose of the clippings responsibly. Don't compost them at home, as eggs or larvae could survive and spread.
Instead, bag up the waste and take it to a local recycling centre that handles green waste or follow your council's guidance.
It's also a good idea to clean your tools afterwards to prevent spreading the caterpillars or their eggs to healthy plants.
Careful disposal plays a big role in limiting the spread of the box tree moth - especially in areas where it's already established, the specialists at Arbtech explain.
Pruning stimulates new, soft growth, which is exactly what box tree caterpillars love to eat.
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To avoid attracting them, try not to prune during peak activity months (usually April to September).
If trimming is needed, do it in late autumn or winter when caterpillars are inactive. Over-pruning in summer not only weakens the plant but also makes it more attractive to egg-laying moths.
Keeping your box plants in good shape without excessive cutting will help reduce their vulnerability to infestations and keep your garden looking healthier for longer.