Dear Readers, I was shooting the breeze with a few friends while leaning on this fence next to Coldfall Wood when I noticed two things. First up, just look at all those oak seedlings! Some trees were felled here earlier this year (long story and a sad one), but all these little trees have sprung up. It makes me think that the density of planting in the Tiny Forest movement really does mimic what happens naturally when a tree falls – everything germinates in the unexpected light and heads towards the sun in a great botanical race.

Secondly, though, what are those lovely little orange things in the middle of the patch?

Well, I do believe that these are oak marble galls, and they have a very interesting story. First up, these structures are the homes of the larvae of a tiny wasp Andricus kollari, who lays its eggs on the bud of a pedunculate oak (one of our two native species) . When the larvae begins to feed, the oak itself produces this ‘gall’ instead of a bud, as a result of interaction with the chemicals produced by the larvae. Each gall protects one larva, although the wasp doesn’t always have things its own way – various parasites may also move in. However, in August the adult insects leave, and the galls fall from the tree., as in the photo above.

An Andricus wasp (Photo By Dl sh ad – Own work, CC BY-SA 4.0, https://commons.wikimedia.org/w/index.php?curid=55391400)

All the wasps that emerge from the marble galls are asexual females – they are carrying self-fertilised eggs. In the spring, they seek out a different kind of oak, a turkey oak (which is a non-native tree) and lays their eggs on the buds. The developing larvae give rise to a completely different kind of gall, which looks like a kind of pale banana.

Andricus kollari sexual generation galls nestling in turkey oak bud (Photo by M Chinery from https://www.britishplantgallsociety.org/cynipid/)

These galls mature in March, and when the wasps emerge they are the ‘sexual generation’ – the males and females who emerge mate, and the females head off to find the bud of a pedunculate oak in order to lay their eggs, and for the circle to start all over again.

Although the wasps clearly make the buds that they use for their larvae unviable, they actually cause very little damage to trees, and often prefer trees that are already in decline. Which is just as well, as these tiny insects were deliberately introduced to the UK early in the 19th Century, because the galls were thought to be a useful source of tannin for dyeing and tanning – before this, the East India Company had a licence to import galls from other parts of the world, especially Syria which was the home of the Aleppo gall. As the turkey oak was introduced to the UK in 1735, the wasp already had everything that it needed for a complete life cycle (and I shall be paying more attention to the few turkey oaks in Coldfall Wood in the spring to see if I can see any galls). However, the marble oak gall produces only 17% by weight of tannin, while the Aleppo gall has 4 times as much, so I suspect the industry was short-lived. However, oak galls have been a source of ink for millenia – the Dead Sea Scrolls contain traces of oak gall ink. Sadly, the ink does not last, and over time it discolours and can damage the paper that it was written on.

Nonetheless, the galls have provided food for all manner of creatures – woodpeckers, bank voles and field mice  will crack the galls open in the search for larvae, and lots of small insects will make their homes in the galls (these are known as inquilines – how I love a new word!). And then numerous wasps will parasitize the larvae of the gall wasp. One gall, of a larger kind known as an oak apple, was kept in a container to see what would hatch out, and no fewer than 12 insects popped out!

Oak marble gall that’s been predated by a bird

And look, I have found you a poem, and a beautiful one at that. ‘Gall’ is by Catriona O’Reilly, an Irish poet now living in the UK. See what you think.

GALL

Those from Aleppo were bitterest,
yielding the vividest ink. More permanent
than lampblack or bistre, and at first pale grey,
it darkened, upon exposure,
to the exact shade of rain-pregnant clouds,
since somewhere in the prehistory of ink
is reproduction: a gall-wasp’s nursery,
deliberate worm at the oak apple’s heart.
We knew the recipe by heart for centuries:
we unlettered, tongueless, with hair of ash,
the slattern at the pestle, the bad daughter.
But all who made marks on parchment or paper
dipped their pens in gall, in vitriol; even
the mildest of words like mellow fruitfulness,
of supplication like all I endeavour end
decay equally in time with bare, barren, sterile;
the pages corroding along all their script
like a trail of ash (there is beauty in this)
as the apple of Sodom, the gall, turned
in the hand from gold into ashes and smoke.