top of page

Oaks Don’t Make Apples

Ever heard of "oak apples"? Those balls are from a wasp, not a fruit. Oaks have acorns and balls. Balls called galls.

gall ("oak apple") from Garry oak
Two apples and gall ("oak apple") from Garry oak
oak acorn, oak fruit

And now I’m thinking of acorn pie with apples on top and that would be amazing.  Because acorns are the fruits of oak trees (not the fleshy apple-type but the hard shelled nut-type). 

But usually “oak apple” is more of a joke term that feels very 'southern' to me, and people don’t actually try to eat them.  Well, I have heard stories, be we're being general.  The round ball-things that are formed on either oak leaves or their stems are like an infection and really an organized (hence not quite tumor) growth triggered by any variety of parasitic wasps.  Each type of wasp forms it’s own type of gall, which can vary in shape, size, color, even texture.  Some do kind of look like apples.  And each oak tree has a species or few of wasps that gall it up. 

Wasp "infects" plant stem with an egg --> tree grows extra tissue around it as a triggered response = gall
oak gall wasps

If you collect a few galls and keep them closed in a jar or bag, you may even see the wasp adult emerge from within after living it’s early life stages in the protected gall home.  Hence- the point of the gall growth.  Wasps release growth agents and probably other yet unidentified stimulant chemicals/hormones/enzymes into the oak tissue to trigger the growth of these specific structures so that the wasps eggs and larvae have a safe place to grow and feed until adulthood. Some are triggered by the egg or adult wasp, others but the early feeding of the larvae, probably through its saliva.

mealy oak gall wasp, oak galls, gall wasp

Galls are like if you could tuck your baby against the side of a high-rise building and have the building grow a little baby nursery around it, feeding and protecting your baby until they reach 18.  Aw, now that’s parenting smart!

Galls are not just from insects though. There’s a variety of organisms that can trigger a gall-formation by a host plant, from viruses, bacteria, aphids, even mites which are in the arachnid (aka spider) phylum. Oaks are known to host more galls than any other plant group. Oaks are sexy.

beautiful oak tree

The PNW Garry/white oak trees (Quercus garryana) house hundreds of native insect species to support the broader ecosystem, as do most oaks, including the tiny gall/cynipid wasps.  The cynipid wasps lay their eggs in young stems or budding leaves then their larva's saliva triggers the tissue to produce the gall via a growth hormone. There are 4 main wasp types that form Garry oak galls- Andricus californicus (CA gallfly),  Bassettia ligni, Besbicus mirabilis (speckled gall wasp) and Neuroterus saltatorius (jumping gall wasp).  The prettiest may be this later (B. mirabilis), as they produce a delicately mottled globe gall underneath the oak leaves. 

speckled gall wasp, oak gall, Besbicus mirabilis

oak galls
various oak galls (2 species of oaks)

There’s a wide variety of galls, some pretty and some outright creepy (note- the horned oak gall that looks like an artist’s rendering from an 80’s gory horror movie, brown lumpy with random fleshy horns poking out of it).  Of course, not just oaks or even trees can have galls.  Maples, roses, bramble berries, viburnums, bedstraw, daisies, daylilies, spurge, thistles, etc. etc. have species get galled up as well- woody and herbaceous plants alike. Even flowers get galls.

{See this Gall Society site for all your gall needs:}

herbaceous plant galls
Thistle stem galls - British Plant Gall Society
herbaceous plant galls
daylily flower galls- British Plant Gall Society

The California gallfly are the ones that produce the large “oak apple” galls, due to them being about apple-size and starting green then often turning a yellow-golden color (then turning brownish gray in the fall as they senesce).  Interestingly, the female CA gallflies do this without any males (asexual parthenogenesis reproduction where the females can lay unfertilized eggs that will still produce full offspring). Gall wasps (cynipids) often have a complex life cycle.

These are the smaller galls from live oak trees (Quercus virginiana) in the southern US, formed by the Disholcaspis cinerosa (mealy oak gall wasp).  Some had a mini-capsule inside with the larva still present. It also has 2 galls that are formed for the two different life stages it has in a year.  So this wasp makes a nursery & a high school for it's babies, sorta. 

mealy oak gall wasp, gall wasp, oak gall
wasp from mealy oak gall, still in the small inner capsule, collected in November from live oak

The mealy oak gall has name-sake mealy dry interior tissue when fully formed.  The galls on the oak’s young woody stems have only asexual female wasps that emerge in mid-winter to lay new eggs all by themselves.  Winter is lady’s time for this species of wasp!   But these lay eggs onto a little leaf bud in late winter with the egg & then young larvae holding on through the harsh end of winter to grow and form a new smaller gall on a leaf when the leaf buds expand in spring. Thus growing new leaf galls with a mix of male & female wasp babies inside a smaller pea-size gall that often is unnoticed.  Maybe this spring sexual generation needs to hide more.  Some predators have in fact adapted to find wasp larvae inside their galls. 

life cycle of gall wasps,  Disholcaspis life cycle

When the male & female cynipids emerge late spring (chewing their way out from the center of their galls), they will mate, and fertilized females will lay the asexual eggs on the young oak stems for coming winter’s lone-ladies.  Bisecting-circles of life!  Poor one-purpose males- they mate right after they emerge and then just die. 

 Disholcaspis cinerosa, mealy oak gall wasp
asexual female (winter) D. cinerosa (mealy oak gall wasp)

Though the females are a bit more productive after being reproductive, laying about 15 eggs on new oak stems in just 1 week’s time. That’s a big feat for a tiny wasp.

This gall also makes a sugary secretion that attracts a variety of other insects, including butterflies, which eat the sweet secretions into late autumn when the gall has finished growth & dried up.  Other insects will also move in after the D. cinerosa gall wasp vacates, since there’s now an open home with a small entrance readily available, and will persist for a while on the tree.  The smaller leaf galls aren’t as useful as the oaks will shed their leaves after another 9 months or so, but short lived small insect species may still find inhabit them for a short lease apartment.


live oak gall

The presence of galls supports other species associated with oaks, like carnivorous parasitic wasps who lay their eggs on a gall so their babies can try to burrow in and find the plump larvae inside to eat.  Or some species will just eat the outside of the gall, not interested in the larvae inside, or some insects will share the gall apartment like a mooching uninvited roommate but at least they don’t do any real harm & there’s plenty of room for them.  That’s why you may see several holes in 1 gall. Usually it is 1 cynipid larva per gall.

oak gall, quercus garryana gall, oak apple
Quercus garryana gall (with 2 holes)

Some individual trees, or even stands, are more susceptible to this wasp-egg and gall infection than others and it can vary in load by year as well.  It’s a complex symbiosis.   To summarize:  galls are tree tissue that was manipulated into growth around a wasp egg as it grows into an adult (either a sexual or asexual one) and the bigger spherical mealy oak gall is the home for the asexual generation on the tree stems.  Now exactly how the stimulus to grow the gall around the eggs (or maybe young larvae) can vary and not always known for each gall.  Some may be triggered by the egg being layed but others could be from the feeding of the young larva, perhaps compounds in their little larval saliva.

tough oaks
opuntia cactus growing ON a live oak

Does it hurt?  I mean, are the trees harmed by all these growths, because it does cost them some energy and nutrients?  Well, probably to a small degree.  But it doesn’t make a significant impact on their survival.  The wasps could even be a benefit to the trees in a more indirect way.  Oak trees support a radical amount of highly variable life that uses them in some way.  Tree of life much?!  There’s no real need to try to protect oak trees from these wasps or remove the galls. 

Besides, oaks are so tough a dang big cactus can grow on their truck. Boss!

Besides, you can use the galls!  Not for oak apple pie.  Ew.  And mealy oak galls?  Meally crunchy pie? EwEw.  But you can make something useful and arty from them- Ink.

oak gall ink

With oaks being such a huge part of the culture and landscape in certain areas of Europe, the peoples there figured out how to use even the galls of the various European oaks.  Turns out, a mixture of crushed gall with iron (II) sulfate will create a soft purplish-black or brownish-black ink.  This is possible due to a special acid in the galls, appropriately named “gallotannic acid”.  You can still find, and even make your own, of this ink today. 

Several important “New World” documents in the now American states have been created using oak gall ink- you may have heard of the Declaration of Independence? That was of course from eastern US oak galls.  Even the famous Pliny the Elder used gall ink in his naturalist writings.  Bet you won’t look at those balls the same again.

Oak gall ink isn’t too hard make, just takes a lot of galls, a few ingredients, and some extraction time. 

If you have galls, you can do it!
extracting oak galls, gall ink

1st- collect your galls, lots.

2nd- make iron water for extracting the gallotannic acid

3rd- crush galls & combine, then play the waiting game.

Making Iron Water:

You’ll need iron-rich water to extract and bond with the gall chemicals to make this ink.  Iron water can either be from purchased iron sulfate powder, or home-brewed with rusty metal bits.  Who can’t find that around the house/yard?!  I had a wonderful salvage assistant find a nicely rusted chainsaw chain, screws, old door hinges and I added my own rusty nails & old Texas Ranger (toy?) badge I found (don’t ask) to soak in water with about 1/3rd parts white vinegar, sitting for 3 weeks. 

extracting galls
making rust-water with vinegar
extracting galls

Warning- there is a sort of fermenting going on, producing gasses, so it will leak out of a sealed jar, so I suggest leaving room in the jar and leave open but close lid to shake up on occasion. 

It ballooned up like a weird rust cake a few times, so keep a container underneath & watch the science experiment unfold. Mmm, rusty vinegar water juice home-brew! 

After the 3 weeks, strain out any solid stuff from the iron vinegar water solution. 

extracting oak galls

To make any quantity of ink: 9 parts oak galls, crushed + 2 parts iron sulfate (or “iron water” instead of the distilled water) + 30 parts distilled water. Some recipes include whole cloves & gum arabic but I kept my mixture minimal because I will not be writing a declaration with it.


Combine the crushed oak galls and iron water (or iron sulfate + distilled water) into a glass jar and allow to ferment 2 months. (If the jar has a metal lid, use a barrier between it and the ink when you screw it on.)

extracting oak galls, gall ink
Galls soaking in iron water, already looking black

Strain out the gall chunks. You can add cloves or gum for preservatives but I was ready to write/paint with mine right way. Maybe a gall ink scarf or something would be fun.

Of course galls from different species of oaks will have different amounds of gallotannic acid in them, lend slightly different tones as well, so there is plenty to play with. I had a bunch of live oak mealy galls, so that's what my ink is from. I'll try some Garry oak galls/apples next when I'm among them in the PNW more. Would take less as they are much bigger and I have plenty of iron water left.

And yes, this ink kind of smells like blood (the iron)...

I was wondering how it compares with just the iron water which was fairly dark rust-colored on its own. There definitely is a difference, especially if you cook down the gall ink a bit.

gall ink

Got the “natural dyes bug” already?  Because oh-wow are there more nature items that can make soft dyes for fabrics- berries, onion skins, avocado skin (makes pink!) and even from the mighty oaks giving not just gall ink but also a nice black-gray from acorns.  Dig up some recipes off the web or from several books I’ve seen floating around the natural-dyes world and start making your own home-brew clothes like the plant-weirdos we so enjoy being.


gall ink, using oak galls



Recent Posts

See All


bottom of page