Yponomeuta cagnagella

Euonymus caterpillars. (Photo: Tawny Simisky)
Scientific Name: 
Yponomeuta cagnagella
Common Name: 
Euonymus Caterpillar
Growing Degree Days (GDD's): 
95–600 GDD's, Base 50F, March 1st Start Date. (Source: Robert Childs, UMass Extension.)
Host Plant(s) Common Name (Scientific Name): 
European spindle tree (Euonymus europaea) *Preferred host.
Japanese euonymus (Euonymus japonicus)
Spreading euonymus (Euonymus kiautschovicus)
Winged euonymus (Euonymus alatus)
Insect Description: 

The euonymus caterpillar is the larval form of what is also sometimes referred to as the spindle ermine moth. This is a species of European origin that is now relatively widespread in the United States following its first detection in the Canadian province of Ontario in 1967. Female moths lay eggs in mid to late July, typically on the twigs, branches, and near buds of its hosts. Eggs are covered by the females with a gummy secretion that eventually hardens and makes the eggs difficult to see. Eggs are said to hatch by August and the tiny, immature larvae spend the winter hidden within the eggshells. These larvae are inactive until the following year, when caterpillars group together to feed on newly emerging leaves, creating a mess of webs as they feed. Mature caterpillars are just under an inch in length, creamy yellow-gray in color with black spots and a black head capsule. By late June, these larvae pupate in white, oval-shaped cocoons which are typically oriented together vertically either on host plants or non-hosts in the area. Cocoons can be found in cracks and crevices, or webbed together leaves. The adult moth emerges in late June in most locations. Adult spindle ermine moths are white with black spots and a wingspan of approximately just under one inch. There is one generation per year. (Two other very closely related species in this same genus feed on hawthorn and/or apple.) 

For video footage of the life stages and life cycle of this insect, visit: InsectXaminer.

Damage to Host: 

Caterpillars primarily feed on the foliage of the tree form of euonymus (E. europaea) but will defoliate others. Make silken webs around the foliage as the larvae feed in groups. Plants may be partially or entirely defoliated. In heavy infestations, the webbing from these insects will coat the entire host plant, as well as the ground and/or turf below. Caterpillars also use particularly strong strands of webbing to drop from their host. 

Monitoring: 

Search for caterpillars feeding on newly emerged foliage in the spring, growing larger and more noticeable by the end of May and the beginning of June. Scout for caterpillars while webbing and feeding is still small and limited. 

Cultural Management: 

Avoid planting Euonymus spp., many of which are also considered to be invasive plants with the tendency to outcompete native species and disturb native ecosystems. 

Natural Enemies & Biological Control: 

Various parasitoid wasp species and a predator of the spindle ermine moth are listed on the Invasive Species Compendium (ISC). The extent to which they manage euonymus caterpillar populations in Massachusetts is not currently understood. 

Chemical Management: 

Abamectin (NL)

Acephate (NL)

Acetamiprid (L)

Azadirachtin (NL)

Bacillus thuringiensis subsp. kurstaki (NL)

Beauveria bassiana (NL)

Bifenthrin (NL)

Chlorantraniliprole (NL)

Chlorpyrifos (N)

Cyantraniliprole (NL)

Flonicamid + cyclaniliprole (N)

Horticultural oil (L)

Indoxacarb (L)

Insecticidal soap (NL)

Malathion (L)

Methoxyfenozide (NL)

Neem oil (NL)

Pyrethrin+sulfur (NL)

Spinosad (NL)

Tebufenozide (NL)

Notes: 

Active ingredients that may be applied systemically include: acetamiprid (injection), chlorantraniliprole (soil drench), cyantraniliprole (soil drench, soil injection), and neem oil (soil drench).

Make insecticide applications after bloom to protect pollinators. Applications at times of the day and temperatures when pollinators are less likely to be active can also reduce the risk of impacting their populations.

Note: Beginning July 1, 2022, neonicotinoid insecticides are classified as state restricted use for use on tree and shrub insect pests in Massachusetts. For more information, visit the MA Department of Agricultural Resources Pesticide Program.

Read and follow all label instructions for safety and proper use. If this guide contradicts language on the label, follow the most up-to-date instructions on the product label. Always confirm that the site you wish to treat and the pest you wish to manage are on the label before using any pesticide. Read the full disclaimer. Active ingredients labeled "L" indicate some products containing the active ingredient are labeled for landscape uses on trees or shrubs. Active ingredients labeled "N" indicate some products containing the active ingredient are labeled for use in nurseries. Always confirm allowable uses on product labels. This active ingredient list is based on what was registered for use in Massachusetts at the time of publication. This information changes rapidly and may not be up to date. If you are viewing this information from another state, check with your local Extension Service and State Pesticide Program for local uses and regulations. Active ingredient lists were last updated: January 2024. To check current product registrations in Massachusetts, please visit: https://www.mass.gov/pesticide-product-registration .