How to get started?

Gall Week is starting in less than a week! During Gall Week we will try to document the incredible diversity of galls. Galls are little structures on plants, induced by a few different groups of organisms, mostly insects. They often have interesting shapes, and many of them are colorful and objectively pretty. They can be found on leaves, stems, buds, and even roots. For a good background about galls, listen to this podcast interview with Adam Kranz from Gallformes -
For Gall Week, we are interested in documenting the galls themselves or the gall inducers (adult wasps for example). If you're lucky, you might be able to document one of their associated species - parasitic or inquiline wasps trying to lay their eggs into the galls. We could add these to the project as well.
Since all galls are a result of an interaction between the gall inducer (such as a wasp) and the plant host, it is highly important to document the plant species as well. It is highly important for their identification. Please add the plant name in the observation's comments, and if possible in the "fields" as well. If you're not sure about the plant ID, you can post it to iNaturalist as well, and link that to the gall observation. Please note, you will have to add each observation to this project manually.
---if you've never looked for galls before ----
I'd suggest finding out what are the best host plants in your area. In the West: Oaks, Willows, Coyote Brush, and poplar, among many others. In the East: poplars, willows, and goldenrods (please correct me if I'm wrong). You can find them easily on iNaturalist. Try searching first for gall photos, so you'd know what to look for.
I'd like to share a few resources people can use in order to get started. Please feel free to add more - there are many great resources out there - let's share them! Are there any great books/ websites/ iNat projects that you love using? Please add them in the comments.
Here are a few suggestions, especially for the west:

Posted by merav merav, September 29, 2021 01:18


In the northeastern US, I find lots of galls on oaks, in addition to poplars, willows, and goldenrods. Occasionally, I find galls on hickories, maples, sumacs, and jewelweed. Another resource I use all the time is Charley Eiseman and Noah Charney's book, Tracks & Signs of Insects and Other Invertebrates: A Guide to North American Species. It includes more than just galls, though, so be forewarned that you might get sucked into looking for leafminers and exuviae and webs and all matter of odd, yet fascinating, stuff.

Posted by lynnharper about 1 year ago (Flag)

Participants in this project might find my notes on the (astonishing and growing) number of gall-making insects on goldenrods helpful, particularly in Eastern North America.

Posted by ddennism about 1 year ago (Flag)

For East Coast gall beginners, in the fall, for plants with more than one type of gall, I'd look for oaks, goldenrod, maple, hackberry, hickory, willow. Oak and goldenrod are by far the most commonly noticed by beginners. Poison ivy, red-cedar, and witch-hazel, and black cherry each have one main gall species, but they are common and easy for beginners to spot.

Look especially at the leaves of trees, the stems of vines and prickly canes, and the stems of fall flowering plants, plus look for black or white circles on the leaves of goldenrods, greenbriar, and maple.

Posted by srall about 1 year ago (Flag)

For desert-dwellers, creosote bush (Larrea tridentata) hosts a variety of Asphondylia midge galls, from the large and distinctive Asphondylia auripila to several small and more challenging leaf galls. There are 15 named taxa, with one additional unnamed scimitar-shaped terminal bud gall noted in Ron Russo's recent guide.

Posted by stevejones about 1 year ago (Flag)

These are great, thank you so much for posting!

Posted by merav about 1 year ago (Flag)

For the gall week, are we counting leaf spots and other sort of seemingly two-dimensional leaf infections as galls? It's hard to draw a line between Asteromyia carbonifera and Rhytisma acerinum, for example.

Posted by mws about 1 year ago (Flag)

That's a great question, @mws. I'm not too familiar with the species, but I think since one of them is a gall midge, it should be in. Not sure about the fungus. Is it considered a gall inducer anywhere? Here in California, we can check stuff like that in our gall guide - Russo 2021. Another option - is it on the local iNat gall projects?

Posted by merav about 1 year ago (Flag)

Great project that allows me to see so many types of galls elsewhere in (parts of) the world. I am not an expert in anything, and much less in galls. May I ask if there are less types of galls/less types of gall inducers here in south-central Canada than elsewhere ? Or is it just possible that I don’t what to look for and where ? Note that my glasses are new. Thanks for the input.

Posted by seraphinpoudrier about 1 year ago (Flag)

@merav in Ontario we mostly use the galls of north america project and the non-metazoan plant diseases of north america project. I typically sort anything that builds a structure as a gall and anything that appears flat as a plant disease (leaf spot) but it's fuzzy when a disease looks flat but still goes deeper than the surface of the plant (mildews and some rusts being surface-level examples). It's really only important what we as a group decide to do for the project

Posted by mws about 1 year ago (Flag)

@seraphinpoudrier South-central Canada likely has tons of galls, but very few observers. Canada has very few observers outside of Ontario and BC as is, and only a very small portion of observers regularly observe galls. Another problem is the time of year. I see most of my galls on leaves, and at this time of year in Ontario we're already losing lots of leaves. I imagine the trees are nearly bare in the prairies.

Posted by mws about 1 year ago (Flag)

Thanks @mws for your (quick) feedback. Lots of (yellow) leaves in trees and on the ground here. I’ll keep looking, and keep hoping more observers will join!

Posted by seraphinpoudrier about 1 year ago (Flag)

@seraphinpoudrier I find that once leaves turn yellow, you can only find the galls that are built into the leaves. Lots of oak galls seem to be just slightly connected to the leaf. Those loose ones often fall off once the leaves start to yellow. I'd focus on green leaves and stem/twig galls.

Posted by mws about 1 year ago (Flag)

In southeast I also suggest bald cypress & grapes for multiple species. For single but easy to spot species, I suggest red bay (gall: Trioza magnoliae), blueberries (gall: Hemadas nubilipennis), and sweetleaf aka horsesugar (gall: Exobasidium symploci).

Bonus knowledge: Exobasidium symploci is a fungus induced gall that is edible.

Posted by lappelbaum about 1 year ago (Flag)

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