What are those? How strange! Such was my reaction when I was strolling through a California patio garden. Just above my chest height, a drooping oak limb’s red polka dots caught my eye. Hersey Kiss-like tiny red growths on most of the leaves on this hanging branch. Hundreds, perhaps thousands, of the red cones dotted the leaves up into the tree. What are they?!
My excellent research skills led me to believe that these red, cone-shaped, gall-like structures could be the galls of Red Cone Gall Wasps. Imagine that! Actually, I wish their identification was so speedy and easy. My first inclination was that the pretty red tents were an insect egg, but of course they are not. Galls they are; I had learned something new to boot! These galls are considered “controlled galls” because they take on a specific structure, shape, and size — unlike some galls that look like an undefined blob of plant material.
Galls are the abnormal growth of plants; animal galls occur as well but this article’s focus is on plants. Plant galls are caused by mechanical (for example, friction from rubbing branches) and chemical intrusions on a plant. Among the chemical disturbances that cause plants to gall are viruses, fungi, mites, nematodes, and insects. Insects are the major causal agents of galls in the US. And of all the insects in the U.S., only a few group of flies and wasps create the majority of plant galls. One third (1/3) of galls are caused by tiny Cynipid wasps. Cecidologists (people who study galls) say so!
Red Cone Gall Wasps (Andricus kingi) are to blame, or honor as the flavor of this blog would have it, for the colorful, red cone covered, polka-dotted oak branches we see on oaks. Andricus kingi are cynipid wasps, a huge family of tiny wasps. The female wasp ovideposits (lays eggs) on an oak leaf and the gall forms on the leaf. Usually the underside of the leaf is used. Entomologists/cecidologists are still debating just HOW the galls are formed. But I did find a fascinating description of how an eating “larva may exude a substance that mimics a plant growth chemical called an auxin.” The plant grows bigger/thicker/more shapely at the site of the larva’s contact with the plant.
The cynipid wasp, our beloved Red Cone Gall Wasp, matures and metomorphosizes in the gall, to emerge as an adult wasp. Fly, fly away cynipid wasp!
The cynipid wasp will be both predator and prey in our wildlife garden. The larvae will be confined to the galls but have also carved out their niche in Nature. Among other tasks, they will eat the galls and become prey to insects and birds.
Tony’s Quest for the Red Cone Gall Wasp galls. This video was photographed along the Laguna de Santa Rosa, Sonoma County, California, Sept. 2013.
Enjoy the polka-dotted oak trees and your wildlife garden.
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