A galling field guide

Galls are strange, bulbaceous objects often found on plants and trees. They consist of plant tissue, but have been induced by insects, bacteria or fungi. A classical example of gall-inducing insects are the gall wasps. Their galls are often rather "galling" and conspicuous, including the well known oak apples. Other insects that create galls include aphids, tephritid fruit flies and gall midges.

Ron Russo's "Field Guide to Plant Galls" is a field guide to galls found in California, but can be used in other Western states as well. The field guide section contain colour photos of the galls and descriptions of both galls and gall-inducers. Most of the gall-inducers aren't illustrated, however. A few species not yet described by science have been included.

The book also contains a more general section on the natural history of both galls and gall-inducers. The life of a gall-inducing insect isn't a bed of roses, it seems. They and their galls are frequently attacked by inquilines, parasites and predators (such as birds or rodents). The galls of gall wasps have a fascinating defence strategy: they secrete a kind of honeydew which attracts ants or wasps, thereby keeping parasites away. Some galls have been used in Native American medicine or even sold as food. Another popular use for galls is to produce ink. The author claims that the treaty which ended World War II in the Pacific was signed using gall ink!

"Field Guide to Plants Galls of California and Other Western States" is primarily directed at people who actually want to go out and identify plant galls, but the extensive section on natural history also makes it interesting for the general reader. It also contains a reference section for those who want to learn more.