Small ermine moths

Several species of small ermine moth have caterpillars that live gregariously within sheets of extensive webbing on plants. The caterpillars are creamy white with black spots.

Apple small ermine moth ( Yponomeuta malinellus ) on apple

Apple small ermine moth (Yponomeuta malinellus) on apple

Quick facts

Common name: Small ermine moths
Scientific name: Yponomeuta spp
Plants affected: Hawthorn (Crataegus), apple, Sedum, bird cherry (Prunus padus), Prunus spp, Euonymus
Main symptoms: Defoliation and webbing 
Most active: April to July

What are small ermine moths?

Small ermine moths are white with black markings, they have a wingspan of approximately 20mm and belong to the moth family Yponomeutidae. The creamy white, black marked larvae reach 20mm in length and feed gregariously under the cover of a dense silk webbing. There are several species that are often found in gardens, these include:

  • The common small ermine, Yponomeuta padella. Found on hawthorn, blackthorn and wild cherry, but not bird cherry (Prunus padus)
  • Euonymus small ermines, Y. cagnagella and Y. plumbella. Found on Euonymus
  • Bird cherry small ermine, Y. evonymella.  Found on bird cherry, Prunus padus. This species can cause complete defoliation and spectacular webbing during the later spring and early summer
  • Willow small ermine Y. rorrella. Found on willow, Salix
  • Sedum small ermine, Y. sedella. Found on Sedum
  • Apple Ermine Y. malinellus. Found on ornamental and fruiting apple

Symptoms

Most small ermine moths emerge as adults in July or August, and soon mate an lay eggs. Larvae hatch from late August and overwinter whilst still small. They begin feeding again in spring and are fully grown by June. They can cause extensive defoliation - this and the extensive silk webbing produced whilst feeding make can cause alarm. The caterpillars pupate within the webbing.

The sedum small ermine can have two generations a year with active caterpillars in June-July and September-October.

These caterpillars should not be confused with the webbing caused by box tree caterpillar, cotoneaster webbersbrown tail moth  or oak processionary moth.

Control

Defoliation is most severe on small trees and plants and the webbing can cause alarm, however it should not affect the long term health or vigour of host plants and where possible can be tolerated.

Non-chemical control

Due to the gregarious nature of these caterpillars it is sometimes possible to hand-pick or prune out infested shoots.

Chemical control 

  • Extensive infestations can be treated with an insecticide. Thorough spray coverage is required if control is to be achieved
  • Forceful spraying is needed to penetrate webbing
  • The contact pyrethroid insecticides pyrethrum (considered organic e.g. Bug Clear Gun for Fruit and Veg or Defenders Bug Killer,), deltamethrin (e.g. Provado Ultimate Fruit & Vegetable Bug Killer, Sprayday Greenfly Killer), lambda-cyhalothrin (e.g. Westland Resolva Bug Killer) may have some effect
  • The systemic neonicotinoid insecticide acetamiprid (e.g. Bug Clear Ultra) can also be used
  • 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

Download

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


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