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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
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:
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 webbers, brown tail moth or oak processionary moth.
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.
Due to the gregarious nature of these caterpillars it is sometimes possible to hand-pick or prune out infested shoots.
Pesticides for gardeners (Adobe Acrobat pdf document outlining pesticides available to gardeners)
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