What's eating my thelocactus setispinus?

Thelocactus setispinus (Hedgehog cactus / fishhook cactus) is most commonly bothered indoors by mealybugs and spider mites settling between the hooked spines and areoles. Root rot from excess moisture is a constant risk. Inspect along the ribs and spine bases — the hooked spines make access tricky and pests can establish unnoticed.

White woolly colonies nestled between areoles and at the stem base; honeydew and sooty mould Apply isopropyl alcohol with a cotton swab or fine-tipped brush; spray neem oil solution; quarantine the plant and repeat treatments weekly

Bronze or silver stippling on the cactus epidermis; fine webbing across spine clusters in severe cases Increase humidity around the plant; apply insecticidal soap spray; maintain good airflow to discourage re-infestation

Rounded brown or grey waxy scales fixed to ribs; localised yellowing or sunken pits Scrape off with a soft toothbrush or toothpick; treat with horticultural oil; follow up 10–14 days later for crawlers