Best Gall Hunting Spots in the South Bay Area

Interested in gall hunting? Don’t know where to go? Live in the South Bay Area, or nearby? Or interested in this unique, colorful and interesting natural phenomena? Read on!

I wanted to create a list of the best locations for looking forgalls for others, but also selfishly for myself for next years gall hunting adventures. While this list is by no where near exhaustive, it’s a start, and I’ll update it as I find more good spots. Even Though iNaturalist can basically do this for anyone by using the “explore” tab, I still wanted to create my own curated list. 

A little sampling of local galls

What to look for when choosing a spot for gall hunting:

  1. Oaks.
    1. Oak trees are essential. Valley, coast live, interior live, and blue oaks are the most common oaks with a great variety of galls. 
    2. While other species have galls, from my understanding oaks have the most variety. 
  2. Hills
    1. Hills get you closer to the leaves of a tree on a slope. Hills are your friend! 
  3. Walkability
    1. Both trails and easily walkable hills of low slopes are necessary to be able to get close to the leaves. 
    2. Don’t forget to do a loopy do loop around trees in order to do a proper survey. 

Parks, Preserves and Natural Areas in the South Bay

Guadalupe Oak Grove Park

I had to put the first galling location I perused in 2020 at the top of the list, because it was pretty good, I dare say. I would have loved to visit this park slightly earlier in the year because by the end of September it was pretty dry, but that’s to be expected. 

Galls are at their prime in the fall which is when they reach their most glorious in color and max size. The Bay Area compared to other parts of the US or North America has funny seasons, or kind of lack them in general. So when I say “fall” I probably should say for the sake of galls that could be the beginning of September through October, and perhaps later (tbd). Basically you want to find them before leaves start falling, and the trees aren’t totally quenching for the rains to return. Galls can still be found on fallen leaves, but I personally have very little success finding them on the ground.

This park has a couple good sized hills with beautiful valley oaks which have large drooping branches, fantastic! 

Ulistac Natural Area

Ulistac is a small but mighty restored area in the heart of Northern San Jose. While the quantity of oaks is fewer than other parks, it’s a great place for a pre or post work day walk. 

This is also a great place to learn about native plants, as they have lots of signage. 

Alum Rock Park

Alum Rock has oodles of oaks, as well as many trails to make a trip short or long, flat or hilly. Some trails have many oaks with reachable leaves, while others don’t. But this is when my tip of finding hills comes in. Many of the hilly trails have narrow trails where you can get eye level with the oak’s branches. Scaling these hills are not always so easy, some are quite steep, and better left for the deer, turkey and quails to explore. 

Monte bello Open Space Preserve

The “White Oak trail” is the trail! There is a variety of oaks on this trail such as Shreve, Valley, Canyon, Interior and Coast Live Oaks. More oak variety = more gall variety. Don’t expect to put on many miles while walking on this trail, I think my hubby and I spent two hours and went half a mile . . . maybe. 

The Canyon and Stevens Creek Nature Trail also has oodles of oaks, but the leaves are generally too high up to reach sadly. 

Russian Ridge Preserve

I haven’t gone gall hunting in most of the preserve, but this is another place to do a quick loop on the way to another preserve, or to fill out your day after a smaller hike in the area. 

The loop around Alpine pond with the David C Daniels Nature Center has a few oaks, but it’s the only place we’ve seen Andricus frondeum, a gall with only 24 observations on iNat. So this place has special significance to me, and a place I want to explore further. 

Pearson-Arastradero Preserve

While this preserve isn’t quite in the South Bay, it’s close enough. It’s right off the 280, and with lower traffic levels with the pandemic ongoing it’s a lot quicker to get there than before. 

Any wooded trail here has oaks, but Arastradero Lake has coast live oaks all around the lake’s perimeter and there are valley oaks on the trail from the parking lot to the lake. So, lots of opportunities!

Life Cycle

I can’t resist including an example run down of a gall’s life cycle for anyone who wants a summary. Galls have super fascinating life cycles, and if you know, you know. 

An adult female gall wasp of the Cynipidae Family lays eggs on the emerging tree buds. Once the leaf has matured, the eggs hatch and the larvae are huunnnngry and looking for some grub.  

The larvae start eating the leaf which initiates a signal to the tree to release a growth hormone. The tree then forms the gall structure we see, which comes in all shapes and sizes, all based on the unique tree and wasp species combination! Cones! Blobs! Multiple Blobs! Fuzzy Blobs! 

For the larvae, this is freaking fantastic, more plant tissue to eat! Once the larvae pupate and become an adult, the wasp makes its exit out of the gall through a teeny tiny hole. 

The adult females will wait until the spring to emerge when oaks are producing new buds, and continue the cycle. Totally awesome!

While searching for galls it’s an easy way to find other small insects perusing the leaves, and appreciate leaves in general. Additionally the fall in Northern California can be a bit of a slump in finding new plant species, at least for us, so it’s time to get creative and go a gall huntin’ folks! Yeehaw!

More beautiful galls all found in the South Bay in September/October of 2020

Helpful Gall Identification Resources:

  • iNaturalist Use the “Explore” Tab, and search for Cynipoidea (Gall Wasps and Allies)

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