California hosts a diverse variety of spiders, but the largest species belongs to the tarantula family. The sheer scale of these native arachnids often surprises those unfamiliar with them. The search for the largest species is definitively settled by examining the tarantulas that inhabit the state’s warmer regions.
Identifying the Largest Species
The largest spider in California belongs to the genus Aphonopelma, commonly called California or desert tarantulas. The most well-known species is Aphonopelma chalcodes, which consistently reaches imposing sizes. Spider size is primarily determined by leg span, measured from the tip of the first leg on one side to the tip of the fourth leg on the opposite side. Mature females can have a body length up to 7 centimeters (2.75 inches) and a leg span reaching 12 to 15 centimeters (5 to 6 inches). This size places them far ahead of other large California spiders, such as the Giant Crab Spider, which typically measures only up to 2.5 inches in leg span.
Habitat and Lifestyle
The California tarantula, including Aphonopelma chalcodes, thrives in the arid and semi-arid regions of Southern California, extending into the central valleys and foothills. They are found in environments like grasslands, chaparral, and desert scrub, which provide the dry, well-draining soil necessary for their lifestyle. These spiders are fossorial, meaning they spend most of their lives in burrows they dig or occupy.
Their silk-lined burrows serve as a protected home, offering refuge from predators and temperature extremes. Tarantulas are nocturnal ambush predators, emerging at night to wait for passing prey, such as insects, millipedes, and small reptiles. The best time to observe them is during the late summer and fall, when mature males leave their burrows to search for females in a visible mating migration.
Threat Level and Misconceptions
Despite their intimidating size, California tarantulas are generally docile and pose a minimal threat to humans. They are reluctant to bite, preferring to retreat when disturbed. If a bite does occur, the venom is mild, often compared to a bee sting, and is not medically significant to a healthy adult.
The primary defense mechanism is not their fangs, but the urticating hairs covering the abdomen. When threatened, the spider rubs its hind legs against its abdomen to flick these tiny, barbed bristles toward an attacker. Contact with these hairs can cause localized itching, irritation, or a rash on the skin or in the eyes, serving as a deterrent to predators.