Plant galls are curious structures form when certain insects, most often tiny wasps and flies, lay their eggs on developing plant tissue; somehow, the developing larvae then chemically “hijack” the plant’s growth mechanisms to create a custom-built home specific to that insect, on a specific species of plant. The majority occur locally on rabbitbrush, sagebrush, willows, and roses, and can most easily be seen in winter and early spring. Pictured here are some of the ones most likely to be found in the Boise Front. (Note: labels on photos are morphological descriptions rather than standardized common names).
The study of plant galls is still a wide-open field, with a large percentage of gall-forming species still undescribed, including some of the most common ones in the Boise Front. The best book to learn more about western galls (mostly in California, however) is Ronald Russo’s Plant Galls of the Western United States (2021).