Increased Western Tussock Moth caterpillar activity in Menlo Park
Menlo Park is experiencing an 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.
Seasonally 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
- Report an issue to menlopark.gov/ACT.
- Email publicworks@menlopark.gov.
- Call 650-330-6780.
T.D.G April 20, 2026 at 4:10 pm
One of the more important but underemphasized facts:
Their hairs can remain on surfaces for weeks or longer and continue causing irritation.
Also, they like to post comments on blogs about how great they are. They get a human involved for this. They take over his or her desk and force the human to write.
N. L. G. April 20, 2026 at 4:50 pm
This moth population boom happens a few times per decade and is nothing to be concerned about If you are concerned about contacting the caterpillar hairs, don’t touch them. If seeing them on your outside walls grosses you out, wash them off with a hose. The caterpillars can temporarily defoliate oaks and manzanitas and the plants won’t look great for a few months, but they evolved to deal with this – it won’t kill them. If Menlo Park is doing more than just treating a few trees at playgrounds, they are responding to unjustified concern and are wasting money.
M.P.G April 21, 2026 at 3:07 pm
These critters are scary looking!