Hodari Nundu captured these images of ladder-backed woodpeckers in action. One of them drills insect larvae out of a plant stem and feeds them to the other. This is probably a mother feeding her nearly-grown offspring.
Cornell’s Birds of North America, which is my go-to site for bird info, has this interesting quote about the critter formerly known as the cactus woodpecker:
We have become so accustomed to associating Woodpeckers with big timber, that it strikes us as uncanny to flush a Cactus Woodpecker from a creosote bush at the edge of the desert, and to have it go plinking contentedly from one bit of dwarf vegetation to another. . . . [H]owever much it may forage over the creosote and cholla patches, on occasion, it requires something of more ample girth for a nesting site.
--W. L. Dawson, The Birds of California 1923
The “something of more ample girth” is generally a bigger cactus, especially a saguaro. But, as the photos make clear, the ladder-back isn't limited to cacti when it forages.