Spider veins and varicose veins are both types of venous insufficiency, but they differ in appearance and severity. Spider veins are small, thin, and often red or blue, resembling spider webs. They are typically harmless and may appear on the face or legs. Varicose veins, on the other hand, are larger, swollen, and can be blue or dark purple. They often cause discomfort or pain and may lead to more serious complications if left untreated.