A plague of caterpillars hits Mountain View

Unusual weather fuels an explosion of hairy crawlers all over town

It's hard to get around town without running into them. Hordes of hairy caterpillars, freshly hatched after a warm February, can be found all over Mountain View and neighboring cities dangling down tree branches and wriggling on cars, playgrounds and garbage bins, leaving behind trails of stringy silk.

And while the hairy, crawling critters tend to make their debut around this time every year, Mountain View parks staff acknowledge that there's an usually high number of caterpillars this season, and is taking steps to clear out the pests that have completely overtaken parks, play structures and other public spaces.

The culprit appears to be the western tussock moth caterpillar, which emerge from eggs as black-haired caterpillars around March and April, according to the University of California's Integrated Pest Management program. Mature larvae tend to stick around until mid-spring, when they spin cocoons, emerge, and can continue to pester residents as moths.

Although the city of Mountain View treated trees in the city with a "systemic" insecticide to control the population of caterpillars, hot weather in February diminished its effectiveness. The result is that tree-heavy regions of the city -- including residential yards and some city parks -- have become inundated with a plague of wriggling caterpillars. Residents on the social media website Nextdoor are reporting unusually high numbers of caterpillars at Eagle Park as well as Castro and Mistral elementary schools, and complain that they are putting a damper on outdoor activities.

"Unfortunately our very, very warm February caused an early hatch before the insecticide had been fully absorbed by the trees," Bruce Hurlburt, the city's parks and open space manager, told residents in an email.

Hurlburt told the Voice in an email that this year's infestation is worse than prior years, and that the city is trying to address the nuisance. While they don't pose a health risk, the long "hairs" on the backs of caterpillars can irritate skin and cause a rash when handled. More problematic is the fact that a critical mass of moth caterpillars can make quick work of the leaves on trees, and can completely defoliate the canopy in a matter of days.

Parks staffers are vowing to take action -- at least at city parks -- by blasting play structures with pressurized water and sweeping away caterpillars at locales including Eagle, Pioneer and Rengstorff parks. In the most affected areas, staff will be using an insecticide known as Evergreen Pyrethrum Concentrate to bring down caterpillar populations while minimizing the effect on other insects.

Hurlburt said city staff will be treating areas with the highest concentrations of caterpillars, and will be administering the insecticide into trees through a power sprayer. The spraying will be done early in the morning, and treated areas should be safe to enter about an hour afterward, he said. Residents struggling with their own small-scale invasion can spray off caterpillars with a hose, or, if it's truly problematic, call a pest control company.

Other agencies have sought less chemical-oriented strategies. During a particularly bad caterpillar outbreak in 2007, Stanford University sought an alternative to pesticides by setting the stage for a small-scale war, unleashing spined solider bugs and nematodes as a way to bring down the population of tussock moth caterpillars. Other Stanford documents show the university has sought to use power washing on trees in lieu of insecticides.

We can't do it without you.
Support local journalism.


9 people like this
Posted by Not impressed
a resident of Old Mountain View
on Apr 16, 2018 at 3:26 pm

Glad to hear that the city of Mtn View is "on it". By the time they get to doing anything, the moths will have already flown away.

5 people like this
Posted by Mavis Petra
a resident of Cuesta Park
on Apr 16, 2018 at 3:57 pm

The caterpillars are also very heavy in population in the oak trees along the Stevens Creek Trail. I found them dropping in Cuesta Park, also
from the Oak Trees.
How long will this continue? Having worms drop from silk strands as I am
trying to enjoy nature rather defeats the purpose!!

12 people like this
Posted by Did the mayor invite them?
a resident of Bailey Park
on Apr 16, 2018 at 6:55 pm

Since the mayor invites in homeless in cars, curious if he is associated to this as well?

74 people like this
Posted by Reader
a resident of Another Mountain View Neighborhood
on Apr 16, 2018 at 9:17 pm

Dear "Did the mayor invite them?" (resident of Bailey Park):

The caterpillars were here long before the current mayor and elected city officials. By thousands of years.

Just thought you might like to know.

Have a wonderful evening everyone!

5 people like this
Posted by Yard Defender
a resident of Shoreline West
on Apr 16, 2018 at 10:10 pm

so what are you using to defend your home against this plague of caterpillar?

10 people like this
Posted by Kindness
a resident of Another Mountain View Neighborhood
on Apr 17, 2018 at 12:53 am

It's very sad and selfish to complain about people who don't have a nice warm home with space to walk around, use the rest room and sleep in a warm safe place like you must do. Shame on you! You should be greatful it is not you out there sleeping in car with people like complaining while you are having a hard life already. Silence is golden.

8 people like this
Posted by Mistral Family
a resident of Another Mountain View Neighborhood
on Apr 20, 2018 at 11:32 am

We have kids afraid to go to school at Mistral because of the caterpillars--they are causing rashes and are EVERYWHERE. PLEASE MVWSD--Please TRY HARDER to prevent them at the school in the Fall and kill them in the Spring so our children are not miserable at school. This is affecting their desire to attend school!!!

3 people like this
Posted by School Parent
a resident of Cuesta Park
on Apr 20, 2018 at 1:28 pm

@Mistral Family

This sounds like a First World Problem if this is what kids in this town have to face at their schools

11 people like this
Posted by @Mistral Family
a resident of Another Mountain View Neighborhood
on Apr 20, 2018 at 1:40 pm

This is an uncommon event caused by unchangeable natural factors. They could do nothing, and it would seem like they did something next spring.
The kids will just have to put their big boy/girl pants on and wait for the butterflies.

Oh, or we could flood air with clouds of toxic insecticide sprayed into the trees and all over the ground. That'd work as well.

6 people like this
Posted by Kris Geering
a resident of Rex Manor
on Apr 20, 2018 at 11:43 pm

How, exactly, is your child being covered in an itchy rash a "first world problem?" The rashes can, and have for some kids, gotten so bad that they get infected. It has nothing to do with being entitled, or "first world." They're kids, and they're itching and in pain and can't do anything about it. Seems fairly universal to me.

I think the Voice would find some very interesting stories in talking to parents whose kids have gotten these rashes. I know Mistral has been fairly proactive after last year's debacle, when the children were eating under the oak tree and caterpillars were literally dropping into their food. This year is actually better on campus than most other parks in town...and there are still thousands of caterpillars everywhere, and kids are still afraid to walk outside or go to school.

The city of MV needs to think proactively for next year and do more to treat for them. And they haven't been leaving any "clouds of toxic insecticide;" they've been using pesticides that are natural to be as gentle as possible. The power-washing works in the short-term. With as much brain power as we have around here, surely someone can come up with a better solution?

3 people like this
Posted by CrescentParkAnon.
a resident of another community
on Apr 23, 2018 at 8:05 pm

I have a bush in my yard that gets caterpillars every year, in two waves.
They just about eat the thing down to the wood.
The BT Thuricide (BT) Conc. A liquid formulation of bacteria kills them dead quickly if I employ it soon enough.
I wish Home Depot would not sell plants that do not do naturally well in this area. But the Thuricide is not really toxic and it does not kill other beneficial insects. A bottle costs a lot, but in industrial amounts maybe it is reasonable.

9 people like this
Posted by Baby Birds
a resident of Cuesta Park
on Apr 24, 2018 at 6:25 am

Last week in Cuesta Park I saw 2 instances where nests had been blasted out and the baby birds left on the ground. Are the city workers being told that this is peak hatching season for birds and the nests are full of them?

3 people like this
Posted by Sue
a resident of another community
on May 1, 2018 at 9:51 pm

In willow glen. Broomhill park totally infested. Definitely causing skin rashes to adults and chest congestion

9 people like this
Posted by Some still around
a resident of Another Mountain View Neighborhood
on May 2, 2018 at 6:29 am

They are much less numerous and numbers are declining fast around us. As a nurse at PAMF I've not seen these reactions on patients that some claim to be "Definitely" caused by caterpillars. I think the panic is beginning to subside. How did we ever survive?

Sorry, but further commenting on this topic has been closed.

Don't be the last to know

Get the latest headlines sent straight to your inbox every day.

Barcelona tapas restaurant coming to Palo Alto
By Elena Kadvany | 16 comments | 7,645 views

By Aldis Petriceks | 5 comments | 1,654 views

Couples: Reading List
By Chandrama Anderson | 0 comments | 1,201 views