Western Tussock Moth caterpillar activity

Published on March 30, 2026

Caterpillars

Menlo Park is experiencing a seasonal increase in Western Tussock Moth caterpillars affecting coast live oaks. These native insects typically appear during the spring and summer and, while noticeable, are a temporary occurrence that resolves naturally. 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 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

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