Aphonopelma marxi, commonly known as the Grand Canyon Black tarantula, is a high-altitude species native to the southwestern United States. It is particularly noted for its dark, "fluffy" appearance and its presence in the "Four Corners" region. 
 
Physical Characteristics
Coloration: They are generally dark brown to black and very hairy, often displaying orange to red hairs on the abdomen. Freshly moulted individuals appear deep black.
Size: They are relatively small for tarantulas, with a leg span often around 3 to 4 inches (7.5–10 cm).
Females: Larger, with a body length around 1.4 inches (35 mm).
Males: Generally smaller, with a carapace length of 8.3–10.5 mm.
Identification: It can be distinguished from similar species by specific limb ratios and its distinctive hairy, dark appearance. 
 
Habitat and Distribution
Range: Found in high-elevation areas (often above 6,000 feet) across Arizona, New Mexico, Colorado, and Utah.
Environment: They inhabit mixed conifer forests and sagebrush steppe.
Burrows: They are terrestrial, opportunistic burrowers. Their burrows are described as "incredibly difficult to find" because they are often well-hidden. 
 
Behaviour and Lifecycle
Temperament: Generally considered docile and suitable for beginners, though they can be skittish.
Activity: Most of the year is spent in burrows. During the fall, mature males can be seen wandering during the day in search of mates.
Lifespan: Like other Aphonopelma species, females are long-lived (potentially 20–30+ years), while males live significantly shorter lives, often dying shortly after reaching maturity.
Defence: They possess mild venom that is not medically significant to humans, similar to a bee sting. Their primary defence is flicking urticating hairs from their abdomen. 
 
Taxonomy
First described in 1891, the species now includes Aphonopelma behlei and A. vogelae as synonyms following a 2016 revision. It belongs to the "Marxi species group," a collection of mainly black, high-altitude tarantulas.