Elm: Spiny elm caterpillar
Photo by: S.J. Collman
Biology
The spiny elm caterpillar is the larval stage of the mourningcloak butterfly. The adult is approximately 2 1/2″ across, with purplish brown to black wings bordered by a creamy yellow stripe and a row of blue spots.
The larvae are purplish black with white specks and have a row of orange to red spots along the back. They also have long forked spines on their bodies.
The caterpillars often feed in large groups and eat all the leaves on a branch before moving. Their feeding results in raggedly chewed leaves.
Spiny elm caterpillars also feed on willow and poplar trees. They are not a serious pest.
Management Options
See "Using Integrated Pest Management (IPM) in the Landscape" for successful problem management techniques.
Non-chemical Management
Select non-chemical management options as your first choice!
- Hand-pick and destroy caterpillars, if desired.
- Prune and destroy heavily infested branches.
Chemical Management
IMPORTANT: Always read and follow label directions when working with pesticides.
For more information on using pesticides visit :
- Apply when caterpillars first appear.
- If Bt is chosen, be sure to apply when insect is feeding.
- Best time is when caterpillars are young.
- Use a spreader-sticker with liquid Bt formulations.
- Homeowners should not make foliar applications to trees over 10 ft tall.
- Consult a commercial pesticide applicator for treatment of trees and shrubs over 10 ft. tall.
Approved Pesticides
If you choose to use a pesticide, some examples of products that are legal in Washington are listed below. Some products are labeled for just INDOOR or just OUTDOOR use, or may allow both uses. Be sure to choose a product appropriate for your situation. Always read and follow all label directions.
Additional Image
Photo by: S.J. Collman
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Evidence of noncompliance may be reported through your local Extension office.