Plant Problem Diagnostic
Box Tree Caterpillar: Identification and Control
The short answer
Box tree caterpillar is the larva of the box tree moth (Cydalima perspectalis) and has become the most reported pest to the RHS. Look for green-and-black caterpillars with black heads inside fine webbing among box (Buxus) foliage, along with pale patches and stripped, skeletonised leaves. The caterpillars often feed hidden inside the bush, so early damage is easy to miss.
The practical approach is to detect early and remove by hand. Pheromone traps tell you when adult moths are active in your area so you know to search for and pick off caterpillars before they cause serious damage. A mixed nematode biological control has some effect, and severe infestations may need repeated action. In the US and Canada the moth is a regulated pest under USDA APHIS and CFIA quarantines, so report suspected sightings to the authorities there.
How to recognise box tree caterpillar
Caterpillars are greenish-yellow with black and white markings and a black head, growing to around 4cm. They live within webbing spun over box foliage and stems, and their feeding causes pale patches, defoliation and skeletonised leaves. It is easy to confuse the damage with box blight (a fungal disease), so look for the caterpillars and webbing themselves.
- Green-and-black caterpillars with black heads inside fine webbing on box (Buxus)
- Pale patches, stripped leaves and bare stems, often starting deep inside the bush
- Distinguish from box blight, which causes leaf spots and dieback without caterpillars
Monitor and control
- 1Trap to monitor — Hang a box tree moth pheromone trap (sold by suppliers such as Agralan, Dragonfli and Solabiol) to show when moths are active in your area.
- 2Search and pick — When traps show activity, or from May onwards, check plants frequently and remove caterpillars and webbing by hand where practical.
- 3Consider biological control — A mixed nematode product sold for fruit and vegetable protection has some effect on the caterpillars; use it with care as nematodes can affect non-target insects.
- 4Repeat as needed — There can be several generations a year, so keep checking through the season and act before a population becomes damaging.
US and Canada: a regulated pest
Box tree moth was first found in North America in Toronto in 2018 and confirmed in New York State in 2021. USDA APHIS and the Canadian Food Inspection Agency (CFIA) run quarantines and import restrictions on boxwood (Buxus), spindle (Euonymus) and holly (Ilex) to slow its spread, with regulated areas in several US states. If you suspect box tree moth in North America, report it to APHIS or your local CFIA office rather than only treating it. See our guide on growing and pruning boxwood for keeping plants healthy.
⚠ In the US and Canada, box tree moth is a quarantine pest. Report suspected sightings to USDA APHIS or the CFIA; do not move boxwood plants that may be infested.
Sources
Reviewed 2026-07-18. We cite university Extension, government, and established horticultural sources — and never invent pesticide rates or dangerous treatments.
- RHS — Box tree caterpillar — Most reported pest to the RHS; caterpillars with webbing on box; pheromone traps (Agralan, Dragonfli, Solabiol) indicate moth activity; remove caterpillars by hand; mixed nematode biological control has some effect and should be used with care; monitor from May and early spring onwards.
- USDA APHIS — Box tree moth import requirements from Canada — APHIS restricts import of Buxus, Euonymus and Ilex from Canada to prevent introduction of box tree moth; federal quarantines cover impacted US counties.
- Invasive Species Centre (Canada) — Box Tree Moth — CFIA first detected box tree moth in Toronto in August 2018; encourages reporting samples to a local CFIA office.