The Australian redback spider (Latrodectus hasselti) is one of the widow spiders (Latrodectus), a cosmopolitan group of small, round-bodied spiders.

Female redback spiders are black (occasionally brownish) with an obvious orange to red longitudinal stripe on the upper abdomen, with the red stripe sometimes being broken, and an hourglass-shaped red/orange spot on the underside of the abdomen. Females are about a centimeter long, but males are just a few mm. The males' red markings are often less distinct. The male's body is light brown with white markings on the upper side of the abdomen and a pale hourglass marking on the underside. Juveniles have additional white markings on the abdomen (http://australianmuseum.net.au/Redback-Spider, accessed 24 December 2009)