What's eating my coryphantha elephantidens?

Coryphantha elephantidens, a large globular cactus grown as a houseplant, is most vulnerable to mealybugs that shelter in its pronounced mammillae and axils. Root mealybugs are equally common. Spider mites may cause surface scarring in hot, dry rooms. Good airflow and vigilant inspection prevent most infestations.

White woolly tufts accumulate in the axils between mammillae; plant weakens and may shrivel despite watering. Remove with alcohol-dipped cotton swabs; spray with neem oil solution every two weeks until clear.

Unexplained wilting and looseness in the pot; white powdery coating visible on roots when unpotted. Bare-root the plant, soak roots in imidacloprid solution, allow to dry, and repot into sterile cactus compost.

Bronze or silver stippling on the body surface, particularly on the upper half exposed to dry air. Wipe surface with damp cloth; apply neem oil or miticide and move plant away from heat vents.