The winter moth (Operophtera brumata) is a common pest of trees and shrubs in the UK. This article explains how to identify the winter moth, where it occurs, the damage caused by the caterpillars, and how to prevent and control infestations in gardens, orchards and green spaces.
In everyday use, the pest is called the winter moth, while its larvae are often referred to as caterpillars, loopers or inchworms, depending on the host plant and time of year.
Identification
What do winter moths and their caterpillars look like?
The adult winter moth is a small, brownish moth active late in the year. Males have fully developed wings and can fly, typically from October to November. Females are wingless and crawl up tree trunks to mate and lay eggs.
The caterpillars are slender, green and grow up to about 2.5 cm long. They move in a characteristic “looping” or “measuring” motion, arching their bodies as they crawl, which gives rise to the common name inchworm.
Habitat and Distribution
Where are winter moths found in the UK?
Winter moths are widespread throughout the UK. They are most common in areas with deciduous trees and shrubs, particularly oak, beech and fruit trees such as apple and pear.
Typical habitats include:
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Apple and pear trees in private gardens
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Orchards and small fruit plantations
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Deciduous woodland and parkland
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Ornamental shrubs and hedges
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Woodland edges and shelter belts
Signs of Infestation
How can winter moth caterpillar damage be recognised?
Caterpillars hatch early in spring, usually from April to May. Damage is often most noticeable in the upper parts of trees.
Common signs include:
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Trees with sparse foliage or delayed leaf growth in spring
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Chewed leaves and damaged flower buds
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Holes in newly emerged leaves
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Reduced flowering and fruit set
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Fine webbing in the canopy during heavy infestations
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Caterpillars hanging on silk threads from branches
In fruit trees, repeated attacks can weaken trees and significantly reduce harvests.
Life Cycle
What is the life cycle of the winter moth?
The winter moth has one generation per year and follows this cycle:
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Eggs: Laid in November–December in cracks and crevices of bark
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Larvae: Hatch in April and feed on buds and leaves for 4–6 weeks
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Pupae: Caterpillars pupate in the soil in June
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Adults: Males fly in October–November; wingless females climb tree trunks
The eggs overwinter and are highly resistant to cold, which is reflected in the species’ name.
Prevention
How can winter moth infestations be prevented?
Use sticky bands on tree trunks
Apply sticky bands to fruit trees in October to trap wingless females before they can lay eggs. Check and renew bands regularly.
Prune dense canopies
An open canopy makes it harder for caterpillars to hide and easier to spot early damage.
Remove fallen leaves and debris
Pupae may be present in leaf litter around the base of trees. Keeping the area tidy reduces overwintering success.
Encourage birds
Tits, especially blue tits, feed readily on caterpillars. Install nest boxes and avoid pesticides that harm beneficial wildlife.
Avoid excessive fertilisation
Lush, soft growth is more attractive to caterpillars and other pests.
Control Measures
How can winter moths be controlled?
Manual removal
In light infestations, caterpillars can be picked off by hand or shaken from branches onto a sheet placed beneath the tree.
Biological control
Spraying with Bacillus thuringiensis (Bt) during the early caterpillar stage is effective and selective, causing minimal harm to beneficial insects. Apply in dry weather.
Soil cultivation
Light cultivation of soil around the base of trees in late summer can disturb pupae and reduce numbers the following year.
Monitoring with pheromone traps
Pheromone traps can be used, particularly in orchards, to monitor adult male activity and assess infestation risk.
Avoid chemical insecticides
Chemical treatments should be a last resort and are generally discouraged in home gardens, where natural predators can provide effective control.
Occurrence in the UK
Where in the UK is the winter moth most common?
Winter moths occur throughout the UK but are especially common:
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In older gardens with mature apple and pear trees
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In orchards with limited monitoring
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In woodlands with dense deciduous tree cover
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In hedgerows and small woodland areas near farmland and gardens
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After mild winters, when high numbers of eggs survive
By combining preventive measures with biological control and encouraging natural predators, winter moth populations can usually be kept at manageable levels, protecting both fruit trees and ornamental deciduous trees from severe leaf and flower damage.