US Geological Survey


Date of this Version



The Palmetto Volume 31:1


U.S. Government Work.


Maybe you have noticed these little spheres before – but did not give them much thought. Or maybe, you puzzled: What are these wooden pearls? How did they get there? Well, a tiny wasp, called the pea galler wasp or gallfly, Belonocnema treatae, is the culprit. The diminutive female gallfly (one of nearly a thousand species in the gall wasp family Cynipidae), about the size of a fire ant, lays eggs on a freshly budded live oak leaf in spring. When the larva hatches, it produces a chemical that induces the oak to enclose it in a protective and nurturing gall: nifty chemical subterfuge, producing a durable little house for the gall wasp larva – no house of bricks, but nearly as good – indeed maybe even better. It comes equipped with a food supply as well. At the chemical direction of the larva, the gall provides an inner layer of nitrogen-rich pulp, similar to seed tissue. A tough lignin-rich1 outer layer protects the larva from predators, and a chemical shield of anti-microbial tannic acid is concentrated within. Tannic (or gallotannic) acid concentrated in the gall is the tree’s way of isolating the parasitic larva. Ironically, however, the same phenol-rich barrier helps deter predators and disease. Perhaps the bitter taste of tannins and phenols may also discourage predation of gall larvae by birds.