This cactus does well at the river.
I have only seen this white Cochineal on prickly pear at the river. It is a bug that feeds upon but does not kill the cactus. Scraped off and dried, the web, insects and eggs are processed to make a red dye. Tons of this were shipped back to Spain in the 1500’s. Today the dye is popular in lipstick. (Note: cactus are a New World plant and did not exist in Europe until the discovery of the Americas.)