Identify and report sightings of gypsy moth (Lymantria dispar)
The gypsy moth (Lymantria dispar) is an important defoliator of a wide range of trees and shrubs in mainland Europe, where it periodically reaches outbreak numbers. The original British population of the moth fed on bog-myrtle (Myrica gale) and creeping willow (Salix repens) in the eastern fens, but became extinct in the early 1900s. In 1995 a small colony of the polyphagous European population was discovered in northeast London. Since then the moth has spread and isolated breeding colonies have been found across a large part of south-east England, including in Buckinghamshire, Dorset, Essex, Berkshire and Hampshire. As the females are largely flightless, it is likely that moth eggs from mainland Europe were carried to the original London location on vehicles, wooden packaging or imported timber.
This page will help you to identify L. dispar and its life cycle stages.
- Full grown larvae (caterpillars) can be up to 70mm long
- Voracious appetite
- Feeds on leaves of broadleaf tree and shrub species
- Feeds on conifers when food is in short supply
- Extensive damage to foliage when population densities are high
- Repeated deforestation can cause tree death
Insect Life Cycle
Larvae (April to August)
Gypsy moth larvae hatch from eggs in spring, usually in April. Newly hatched larvae are 2mm long, uniformly dark in colour and very hairy.
- Easily dispersed on silk threads in the wind in a process known as ‘ballooning’
- Feed on foliage through spring and summer
- Body colour lightens as they grow to become brownish-yellow marked with black
- Yellow head is obvious from the front
- Develop a series of distinctly coloured ‘warty spots’ along their backs: 5 pairs of blue spots behind the head and 6 pairs of red spots to the rear
- Spots make caterpillars easy to distinguish from similar species
- Shed their skin a number of times to accommodate their growing bodies
- Grow to 60-70mm long by August
Pupae (June to September)
When fully grown the caterpillars find a suitable place to transform into adults (pupate).
- Anchor to leaves or bark with silk threads
- May anchor to a brick wall, wooden fence or shed if necessary
- Surround themselves in a silk case that hardens quickly
- Caterpillar tissues break down and adult structures form
- Transformation takes about 2 weeks
Adult moths (July to September)
Male and female adult gypsy moths appear quite different from one another; this is known as sexual dimorphism.
- Smaller than females with a wingspan of 3.5-4cm
- Greyish brown with darker brown transverse lines
- Can fly long distances
- Strongly attracted to females by a chemical scent (pheromone)
- Larger than males with a wingspan of 4.5-6cm
- White with a few transverse lines on the forewing
- Threadlike antennae
- Tend not to fly
Adult females lay eggs in batches of 50-800. Each batch is laid in an individual cluster that measures about 3-4cm by 1.5-2.0cm, covered with yellowish-brown hairs that have been deposited by the female moth. Normally these are laid in bark crevices, but in urban areas the eggs may be laid on any sheltered, slightly rough surface.
Newly laid eggs are bright yellow and firm to the touch; hatched eggs are soft and spongy.
If you suspect a Gypsy moth colony outside of the main distribution in London, you should report the sighting to Forest Research’s Tree Health and Diagnostic Advisory Serviceparticularly if the caterpillars are causing significant defoliation. There is no statutory requirement to report findings of gypsy moth, but the THDAS can advise on management and the information from sightings is crucial for monitoring spread and potential increases in damage.
Unlike the oak processionary moth, gypsy moth caterpillars are not a risk to human health.
Forest Research has used pheromones trapsto monitor this insect in the past in London and Aylesbury, but we no longer carry out regular surveys. We know gypsy moth is now widely but thinly spread across a large part of south-east England, but we continue to collate records and monitor population trends.