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Small Ermine Moth

Yponomeuta spp.

Small Ermine Moth, Lesser Ermine Moth, Ermine Moth

A photograph of a Yponomeuta ermine moth on a leaf

Yponomeutidae - Yponomeuta sp..

by Hectonichus. CC BY-SA 3.0

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The small ermine moths are distinctively white with black dots, just like that of a dalmatian. These moths can be a pest on a variety of plants and they feed gregariously meaning they all feed at the same time in large numbers. There are roughly 103 species in the genus, where each is specifically adapted to infest one or two species of plant, used as the main larval food plant. For example, a common small ermine (Yponomeuta padella) feeds upon hawthorn, blackthorn and wild cherry; whereas a Willow small ermine (Y. rorrella) will only use Willow as a host. Despite their differences in food preferences, all these moths look very alike. For this reason, the best way to identify the species on your plant would be to note what plant they were found infesting.
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Traits

These caterpillars feed gregariously, meaning they feed at the same time in large numbers.
These moths provide a reliable source of food for local bird and bat populations.

Appearance

Adult moths in the genus range between 1-2cm. The wings are white marked with black spots. Larvae are creamy-white with black spots reaching 2cm in length. They often accumulate in large groups, producing protecting sheets of silken web that can cover branches of trees.

Symptoms

These moths may defoliate the plants they infest. Webbing may be evident in the plants infested by this moth.

Activity

Crepuscular

Personality

Order

Lepidoptera

Family

Yponomeutidae

Metamorphosis

Complete

Distribution

Worldwide.

Biological treatment

Defoliation is only severe when plants are young and unestablished. In most cases, vigour remains untouched. Caterpillars have many natural enemies including birds, bats, reptiles and predatory insects. If infestations cannot be tolerated the branches affected can be pruned. For small, lighter infestations caterpillars may be picked off plants with gloves and relocated.

Chemical treatment

To successfully target caterpillars through the webbing chemical sprays must be applied vigorously. Contact pyrethroid insecticides may be the best option for this kind of infestation. If sought, check with your local garden centre and please take care to follow the manufacturers' instructions. Check with your local regulating body for guidance on active ingredients and their authorisation for use. Plants in flower should not be sprayed due to the dangers posed to pollinating insects. Be mindful before spraying big plants. It can be difficult, if not impossible, to gain complete coverage of larger plants. In some cases, insect infestations can persist even when chemical sprays are applied.

Attracts

Each species of small ermine (Yponomeuta) has specialised in infesting a specific group, genus or species of plant. Here are a few examples of what the caterpillars may be found on:
Prunus avium cherry blossom

Wild Cherry

Prunus avium

A Prunus spinosa plant with green leaves and black purple berry fruits

Blackthorn

Prunus spinosa

Spindle Trees

Euonymus spp.

A large flowering Prunus padus tree in a park

Bird Cherry

Prunus padus

Willow

Salix spp.

Stonecrop

Sedum spp.

Braeburn Apple

Malus domestica 'Braeburn'

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