Field Notes: Galls

Happy Arbor Day. Love the trees…like a gall…


Galls are abnormal growths of plant material caused by the invasion of an alien entity, typically insects and mites. The gall wasps may be the most famous of the gall-forcing insects. Some galls are balls, some are nut-like, some are leaf-spiky — like the ones above, found in Prospect Park this week –, and some are weirdly wonderful, like the cotton candy-like type below (from the archives).

The plant reacts to the invasion by forming a gall around the invader, which the animal then uses as food and shelter as it develops into its next stage. I opened one up and found the very tiny life form inside. This is an aphid, the witch-hazel cone gall-maker, Hormaphis hamamelidis. The white specks seen in the second picture are the aphid’s wax secretions.

Galls have historically been used for tannic acids, dyes, and inks. 9th and 10th century monks used gallnut inks because of their known permanence. The Aleppo gall was specified for use in inks made for the U.S. Treasury and the Bank of England, among others. In MS and AR, a small gall has been used as food for domesticated animals: these are 63.6% carbohydrate and 9.34% protein. They also have been used for folk medicine and divination (find a spider in one and it means war!). (Fun facts from S.W. Frost’s Insect Life & Insect Natural History from 1942)

One day a couple of years ago in Green-Wood Cemetery, we found these on a oak (oaks seem to have a particular affinity for making galls):

Whoa, you bet this stopped us in our tracks. I believe this to be the wool sower gall, made by a unique partnership between white oaks and a little wasp, Callirhytis seminator.
Pretty wild, huh? And right here in Brooklyn.

Meanwhile, in the great world, other invertebrates come together in the blog carnival Circus of the Spineless for your enjoyment, edification, and, perhaps (nasal leeches) gross-out.

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