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.
Australian stained-glass mirror spider. This species makes a small tangled web in green vegetation and appears to have behavioural patterns similar to redback and grey house spiders, but it is mainly found in eucalyptus forests rather than on the outside of houses and other man-made constructions. Very little else is know about this species, but It is speculated that the silver patches vary in size with the spiders mood.
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.