Western Tussock Moth caterpillar activity
Published on March 30, 2026
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