Cyriopagopus lividus (formerly Haplopelma lividum), commonly known as the Cobalt Blue tarantula, is an Old World species native to the tropical forests of Myanmar and Thailand. It is iconic in the hobby for its iridescent blue legs, though it is highly reclusive and defensive.
 
Physical Characteristics
Coloration: Adult females exhibit a metallic cobalt blue on their legs and sometimes their carapace, while spiderlings and males typically appear brown or bronze.
Size: They reach a leg span of approximately 5–6 inches (13–15 cm).
Lifespan: Females are long-lived, reaching 15–18 years; males have a much shorter lifespan of about 3–6 years.
Sexual Dimorphism: Males are smaller, lighter in color (tan or bronze), and develop mating hooks on their legs upon reaching maturity. 
 
Behavior and Temperament
Defensiveness: This species is notoriously defensive and can be aggressive if disturbed. It often utilizes a "threat pose" (rearing up) and is known for its speed and willingness to bite.
Lifestyle: As a fossorial species, it spends the vast majority of its time in deep, silk-lined burrows and is rarely seen on the surface.
Venom: It possesses medically significant venom. While not lethal to humans, a bite can cause extreme pain, swelling, and muscle cramps. 
 
Habitat and Care in Captivity
Substrate: Requires deep, moist substrate (at least 5–10 inches) to accommodate its natural burrowing instincts.
Humidity: Thrives in high humidity, typically between 70–80%, which is maintained through regular misting and providing a water dish.
Temperature: Prefers warm environments, generally between 77°F and 85°F (25–29°C).
Diet: Primarily feeds on insects such as crickets, cockroaches, and moths. 
Due to its defensive nature and potent venom, C. lividus is strictly recommended for experienced keepers and should not be handled.