Gypsy moth

The brownish yellow and black, hairy caterpillars of this moth can defoliate large areas of a wide variety of trees and shrubs. Since the mid 1990s the European strain of this moth has become established in London and a few surrounding areas.

Gypsy moth caterpillar RHS / Sian Tyrrell

Gypsy moth caterpillar RHS / Sian Tyrrell

Quick facts

Common name Gypsy moth
Scientific name Lymantria dispar
Plants affected A wide variety of trees and shrubs
Main symptoms Large (up to 7cm long) brownish yellow, hairy caterpillars
Most active April to August

What is Gypsy moth?

Gypsy moth is a moth which has caterpillars that can defoliate trees and shrubs, the European strain of this moth has become established in London and surrounds. The adults are sexually dimorphic (the sexes have different appearances); males have a wingspan of 3.5-4cm and are greyish brown, females have a wingspan of 4.5-6cm and are white with a few darker markings.

It is the caterpillars that are often noticed in gardens as they are up to 7cm long and have yellowish heads with hairy brownish yellow and black bodies. There are also a series of 5 pairs of blue spots and 6 pairs of red spots along the body. Numbers of caterpillars can reach high densities and trees and shrubs can be stripped of foliage.   

Symptoms

Large (up to 7cm long) brownish yellow and black hairy caterpillars, with red and blue markings causing defoliation of large parts of  a wide variety of trees or shrubs.

Gypsy moth should not be confused with oak processionary moth, which has dark coloured caterpillars with fine white hairs and is usually only found on oak. Hairs from the gypsy moth do not usually cause as much irritation as those from oak processionary moth.

The caterpillars of gypsy moth are present from April to August and when fully grown pupate on a surface such as the bark of a tree, brick wall or other vertical surface. The pupal stage lasts about two weeks and emerging adult moths are active from July to September. Eggs are laid in clusters of 50-800 on the bark of host plants These clusters are covered in hairs and measure up to 4cm in diameter; the eggs hatch the following spring.

The moth is most prevalent in London and a few surrounding areas. If  you should find gypsy moth outside of these areas please report it to Forest Research.

Control

Defoliation is most severe on small host plants, and whilst a single defoliation even early in the season should not affect the vigour of a host plant, repeated defoliations can have an adverse effect. 

Non-pesticide control

Where plants are small enough to reach the caterpillars can be removed by hand. Although the hairs on this caterpillar should not be irritant, it is advisable to use gloves when handling hairy caterpillars.

Pesticide control

  • If necessary and the plants affected are small enough to be given a complete coverage of a spray the caterpillars can be treated with an insecticide.  
  • Organic contact insecticides containing natural pyrethrins (e.g. Bug Clear Gun for Fruit & Veg, Ecofective Bug Killer). Several applications of these short persistence products may be necessary to give good control
  • More persistent contact insecticides include the synthetic pyrethroids lambda-cyhalothrin (e.g. Westland Resolva Pest Killer), deltamethrin (e.g. Provanto Ultimate Fruit & Vegetable Bug Killer) and cypermethrin (e.g. Py Bug Killer)
  • The systemic neonicotinoid insecticide acetamiprid (e.g. Bug Clear Ultra) is also available
  • Follow label instructions when using pesticides
  • Small larvae are more susceptible to insecticides than older caterpillars
  • Plants in flower should not be sprayed due to the danger to pollinating insects
  • Inclusion of a pesticide product does not indicate a recommendation or endorsement by the RHS. It is a list of products currently available to the home gardener

Downloads

Pesticides for gardeners (Adobe Acrobat pdf document outlining pesticides available to gardeners)

Biology

The native UK strain of gypsy moth which fed on bog-myrtle (Myrica gale) and creeping willow (Salix repens) went extinct in the early 1900s. However, the European form of the insect became established in London during the 1990s. It can feed on a wide variety of trees and shrubs. Large numbers of the caterpillars cause significant defoliation and in North America, where it is also a non-native, the moth can be a serious problem in woodlands and forests. 

Adult moths emerge from pupae during the summer months. Females release a sex pheromone which attracts the males. Eggs are laid in clusters of up to 800 under a layer of hairs. The eggs hatch in spring. Hatchling larvae are 2mm long hairy and dark, as they grow they remain hairy become brownish yellow with red and blue markings, the head is a dirty yellow colour. The caterpillars can reach 7cm long before finding a place to pupate in mid to late summer. The pupae are anchored to vertical surfaces such as tree bark and walls. After two weeks adult moths emerge.


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