What's eating my euphorbia caput-medusae?

Euphorbia caput-medusae, the Medusa's head succulent, has a central boss with radiating snake-like arms that create ideal hiding spots for mealybugs. Its toxic latex gives some natural protection, but pests exploit the crowded arm bases. Mealybugs are the chief concern, followed by root mealybugs in wet soil.

White fluffy colonies tucked at the base of arms where they meet the central tubercle; sticky honeydew on surfaces below. Use a fine-tipped cotton swab dipped in 70% alcohol to treat each colony; follow with neem oil spray every 10 days.

Plant fails to push out new arm growth; roots show white waxy coating when inspected; soil smells sour if overwatered. Remove from pot, treat roots with neem drench, allow to dry for several days, then repot in a gritty free-draining mix.

Faint stippling on the cylindrical arms and occasional fine webbing between the densest arm clusters. Improve air circulation and apply insecticidal soap; repeat weekly until no signs remain.