Box tree moth caterpillar damage: how to spot it and what to do

What the damage actually looks like

The caterpillars eat box leaves and spin webbing over the area they're feeding on, so the first sign is often patchy, papery-looking foliage with fine webbing rather than obvious holes. Newly hatched caterpillars are greenish-yellow with black heads. Mature caterpillars grow to around 4cm, with a greenish-yellow body marked with thick black and thin white stripes, easy to spot once you know what you're looking for.

Left unchecked, caterpillars can also strip bark from stems, which can girdle and kill whole sections of the plant, not just the leaves.

When to start checking

The RHS recommends regular inspection from early spring, with checks stepping up from May onward as moth activity increases. Catching an infestation early, before it's stripped a section of hedge bare, makes a real difference to how much of the plant survives.

What the RHS actually recommends

Where it's practical, the RHS's first suggestion is simply removing caterpillars by hand. For monitoring adult moth activity, pheromone traps (RHS names Agralan, Dragonfli and Solabiol as suppliers) help track when moths are active so you know when to check more closely.

For treatment, a nematode-based product is the RHS's recommended biological control, though they flag it needs some caution around effects on non-target insects. Some trade sources also point to Bacillus thuringiensis (Btk) sprays, which aren't the RHS's own headline recommendation but are widely used and reportedly effective when caterpillars are actively feeding, worth checking product labelling rather than assuming any one product is a like-for-like swap.

If an infestation keeps coming back year after year or a hedge is already heavily defoliated, the RHS's own fallback is honest: consider a different hedge or topiary species if control stops being practical.

What this means for a Kent garden

Box hedging and topiary are common in Sandwich, Deal and the surrounding villages, especially in older, formal gardens, so this isn't a rare problem here. A spring check before growth really gets going, and another through May and June, catches most infestations before they do serious damage.

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