Join iNaturalist members around the globe in hunting for galls during the nine-day week that runs from April 20 to April 28, then add each gall observation to the April 2024 Gall Week project.

To participate, sign up at
https://www.inaturalist.org/projects/gall-week-april-2024-event

Gall Week comes but twice a year, so mark your calendar. This year the last three days of gall week will overlap with the first three days of the City Nature Challenge (held 4/26-29), so some of our gall observations can be part of both projects.

Where will you be in two weeks? Whatever your answer, you can take part in September Gall Week 2023.

See how many different galls you can find starting Saturday, September 2 and continuing through Sunday, September 10! Record the galls as iNaturalist observations. Then, once you have joined the September Gall Week 2023 project, add each of your observations.

Questions or comments? Post them to the Gall Week project's journal.

iNat will host a 9-day gall bioblitz starting April 15th.

Merav, the organizer of Gall Week Spring 2023, writes "This will be our first spring event. Join us and document galls wherever you are at. Please photograph galls between Saturday, April 15th and Sunday, April 23rd. In order to contribute to our project, please join the project, and add your observations manually."

For more info, and to comment, visit the project page.

Identifying California Galls

One great resource is Ron Russo’s recently released (2021) Plant Galls of the Western United States.

The other resource I find extremely helpful is the website www.Gallformers.org, which as of 7/2022 included pages for over 1800 described North American galls, plus numerous undescribed ones.

Here are some other sources to consult for help identifying California galls:

• The species list for this project offers a quick photolist, with the easiest-to-find galls appearing first.
• Joyce Gross's photolists of California oak galls or other California galls are really helpful, especially the one for oak galls.
• My own somewhat idiosyncratic listing of 200+ California non-oak galls, alphabetized by host plant with links to the iNat species page for the gall inducer and to helpful online resources. There is also my new list of California oak galls, a more bare-bones list mainly concerned with which trees host the gall and where on the tree the gall occurs.
• For the SF Bay Area, you can also download and print Merav's photo-brochures showing common spring galls and common fall galls. They are at https://www.bioblitz.club.

Interesting Reading

Floate, Gall-inducing aphids and mites associated with the hybrid complex of cottonwoods, Populus spp. (Salicaceae) on Canada's grasslands (2010). This is helpful for ID of poplar galls in N. America, although it is written as a guide for one area in Canada. Go to this page and download chapter 13.
***Harris & Pitzschke, Plants make galls to accommodate foreigners: some are friends, most are foes Fascinating 2019 article about what constitutes a true "gall" and how gall inducers hijack plants to make galls.

Here's how insects coax plants into making galls This 3/2/2021 press release includes a link to the full article by Korgaonkar et al.

Leather, Simon, Not all aphid galls are the same (2013)

Quilliam & Shattock, Haustoria of microcyclic rust fungi . . . and other gall-forming species . . .(Plant Pathology 2003) Concludes that some but not all Puccinia and Uromyces rusts form galls [extremely difficult and technical; I would love to find a different article on this fascinating topic--Nancy]

Russo, Ron, Confessions of a Gall Hunter (Natural History magazine 2009/2010) on page 20.

Russo, Ron, Plant Galls: Desert Treasures (Fremontia magazine 2010/2011) on page 40.

Nyman & Julkunen-Tiitto, Manipulation of the phenolic chemistry of willows by gall-inducing sawflies. Research showing that gall-inducing insects can have an amazing amount of control over the chemical properties of the galls they induce.

Stone, et al., The Population Biology of Oak Gall Wasps (Annu. Rev. Entomo. 2002).

Video

Eriophid mites: The MOVIE! Spend a minute-and-a-half learning what they look like and watching one crawl a few millimeters.

If you can recommend other sources of information about galls, please share!

Project members looking to learn more about the plant galls of California have been frustrated by the difficulty of obtaining copies of Ron Russo's out-of-print 2006 guide and the absence of updates. So it's terrific to read that Princeton Field Guides will be issuing Russo's Plant Galls of the Western United States in late March of 2021.

The new guide will cover 536 species of plant galls found west of the Rockies. It will include expanded coverage of desert galls and SW oak galls and over 120 species new to science.