Western Tussock Moth Caterpillar Activity

Western Tussock Moth Caterpillar Activity

Published on March 30, 2026

The City of Menlo Park is experiencing a seasonal increase in Western Tussock Moth caterpillars affecting coast live oaks. These native insects appear periodically - especially in spring and early summer - and, while noticeable, are a temporary and natural occurrence that typically resolves on its own. While these caterpillars can cause temporary defoliation of oak trees, healthy coast live oaks are generally able to recover without long-term impacts.

Recent warm weather has accelerated their activity. In response, the Public Works Department is prioritizing treatment in parks and other high-traffic areas. Crews will then shift to City-maintained street trees where severe infestations have been reported. This phased approach addresses areas of highest public impact first while continuing to respond to service requests.

What to know

• Western Tussock Moth caterpillars are not dangerous, but their tiny hairs can cause skin irritation in some individuals.
• They are commonly found on trees and shrubs, where they feed on leaves.
• Outbreaks are cyclical and usually decline naturally due to weather and natural predators.

What the City is doing

The City is uses non-chemical management methods, including:

• Manual removal of caterpillars in high-use areas such as parks, playgrounds and downtown corridors.
• Targeted pruning of heavily affected branches where appropriate.
• Water spray treatments to safely reduce caterpillar presence on accessible vegetation.
• Monitoring and coordination with maintenance crews to address priority locations.

These methods are effective in reducing impacts while protecting beneficial insects, wildlife and the broader environment.

What residents can do

• Avoid direct contact with caterpillars.
• Wear gloves and long sleeves if working in areas where they are present.
• Keep pets and children from handling caterpillars.
• If contact occurs, wash the area with soap and water.
• Stay on designated paths and trails when visiting parks.

For more information

• Report an issue to menlopark.gov/ACT.
• Email [email protected].
• Call 650-330-6780.

• Announcements