Darwin's bark spider (Caerostris darwini) is an orb-weaver spider – a member of the family Araneidae.
Like other spiders of the genus, they display extreme sexual dimorphism, with large females and small males.
Females vary in total body length from about 18 to 22 mm (0.7 to 0.9 in), males being around one third or less of this length, at about 6 mm (0.2 in).[2] In a captive bred population, females were 14 (1.3–195) times heavier and 2.3 (1–4) times larger than males.[6]