U.S. Black Widow Spider, poisonous and dangerous. (also upside-down) << This spider actually seems to be a Red Back spider with the markings on it's back. They're easily confused with Black Widows due to the extremely similar coloring. ~Riley Arachnid
Redback Spider native to Australia is a member of the venomous widow spiders. Other common names include red-striped spider, red-spot spider, jockey spider, Murra-ngura spider, Kapara spider and the Kanna-jeri spider.
The redback spider (Latrodectus hasseltii) is a dangerous spider endemic to Australia. It is a member of the genus Latrodectus, the widow spiders, which are found throughout the world. The female is easily recognisable by her black body with a prominent red stripe on the back of her abdomen. Females have a body length of about 1cm while the male is smaller, being only 3 to 4 mils long. The redback spider is one of few arachnids which usually display sexual cannibalism wile mating.
Redbacks are considered one of the most dangerous species of spider in Australia. The redback spider has a neurotoxic venom that is toxic to humans with bites causing severe pain, often for over 24 hours. An antivenom is commercially available, and since its introduction in 1956 there have been no deaths due to Redback bites.