Go find hickory galls!

I’d like to invite those of you who are interested to go look for galls on hickory leaves. There are 44 phylloxera and 62 cecidomyiid midge species known to make galls on hickories in North America; iNat has 12 and ~40 reported respectively, with most represented by only a few observations. Comprehensive descriptions have been made for both groups and I’ve put together a searchable version of the midge gall key here: https://www.inaturalist.org/guides/12068

Compared to other gall-forming groups, hickory midge galls are extremely underreported because they’re very small and rarely apparent unless you look under the leaf. But if you know to look for them they’re very cool-looking and extremely abundant, especially in areas where hickories occur in clumps. I found 14(!) species of them today in an hour or so of searching in the first place I looked.

Most species are widely distributed in the eastern US but one (which we’re missing) is endemic to Florida (underside of Carya floridana leaves) so bonus points for finding that one.

If you do find some, try to document:
– the host hickory species or its identifying characters (number of leaflets per stem, presence/absence of pubescence on the lower leaf and along the leaf edge)
– the gall’s internal structure
– the top and bottom of the leaf where the gall is attached

Happy gall-hunting!


This is why I love nature and the people who love nature.


How exciting! Thanks for that guide and guidelines!


I love this! I’ll be paying close attention to hickories especially now.


Well, heck. I took some hickory gall photos not but a month or two ago. They’ll be my next upload, and I’ll be on the lookout for more.


Oh, it looks like we have no hickories in BC…but maybe i’ll keep my eyes peeled for Oak galls.


I wish hickories were more common in my area. I know they’re common in some parts of Ontario, but they seem more or less absent from southern york region. I’ll still keep my eye out, though.


That’s nuts! (couldn’t help it)

Welcome to the forum, @doviende :) I have a lot of gall. So do my oaks.


Oh, @mira_l_b mira_l_b. ::groans::

OK, @Megachile, you’re on. Of course, this also means I’ll have to figure out hickories. ::more groaning::


No galls on hickory leaves yet, but look who I found! https://www.inaturalist.org/observations/40043949

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the gall’s internal structure

I usually try not to damage or injure anything I observe, just because I don’t often feel qualified to say “yep, there’s no way doing this could damage this species/habitat/food source/environment.” I feel bad even picking flowers in my garden when they might be feeding something.

Can I assume this is pretty safe with galls, since these insects are reasonably common and produce lots of offspring?


Yeah, gall wasps/midge populations aren’t normally harmed by collection.


Fortunately the hickories are pretty forgiving gall-wise. They’re not the easiest group to ID but there are only a couple cases where the host ID is crucial. Gall structure is usually enough. But again, the nice thing about iNat is that you don’t need to learn the host ID yourself. As long as you get a few good pics, someone else can help ID the plant.

Entomologists routinely kill hundreds/thousands of their study organisms and it’s generally understood to be negligible compared to the astronomical death rates experienced by insects in general. That may not always be true, and if you don’t feel like destroying a gall that’s totally fine–in many cases we can still get and ID, it’s just somewhat less confident in some species pairings.


Can you describe how to go about revealing the gall’s internal structure such that we can take a photo?

I wasn’t sure I would randomly recognize a hickory if I ran across it (although I would recognize the nuts if I saw them on the ground and could look for one). But it seems there is a hickory tree not far from me (as reported on iNat) and it wouldn’t be much of a job to go look at it.

Galls are my new thing! I think I turned a fellow iNat user on to them, as well, when we went out naturing last week.


Nice idea for those in the eastern and central parts of North America. Why not set up a project for the galls so people can post their results.

FYI: Here’s photos and info about a hickory gall caused by a “phylloxera aphid” and found in Missouri: http://springfieldmn.blogspot.com/2019/05/hickory-leaf-stem-gall.html

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I’ve used a knife and my thumbnail; depending on the species they can be very soft or brittle. Using a knife on a flat surface is the best way to guarantee the split goes where you want it (ie straight down the middle, perpendicular to the leaf) and some of the fingernail splits I’ve done have been fairly sloppy.

Welcome to gall-hunting!

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I do the same, I recently acquired a small Swiss army knife to take with me while looking for galls. The blade is thin enough that I can split most galls without squishing them!

So glad you’re starting this thread! And thanks for making the key!! Just by staring intently at the trees nearby me, I’ve stumbled across several of these never-observed-on-iNat or rarely-observed species. For those who are also new to galls, they’re really fun to look for! They come in an amazing array of odd shapes and colors and textures, and I am always excited to find something weird on an otherwise normal-looking leaf haha.

If anyone wants help with hickory IDs, I am willing to give it a shot, feel free to tag me in any unknown hickories! Photos that help with hickory ID: bark, a whole leaf showing the number and shape of leaflets (count about a dozen leaves and see if the number of leaflets varies at all and what those other numbers are, e.g. “mostly 5 leaflets with some 7”), a close-up of the front and back of a leaflet, showing what the margins look like and if there’s any pubescence, the outside of a fruit (if you can find one), the inside of a fruit, showing how thick the shell is and how many “sections” it divides into, and the buds.