there are 2 main venomous spiders in Australia whose bite can kill humans (although no deaths since 1979 when antivenom was made available in 1980):
male Sydney funnel web spider (Atraxis)
found in the region around Sydney
Funnel-web spider antivenom has been given to at least 100 patients since 1980
female Redback spider (Latrodectus hasselti):
found all over Australia and is common in urban garden sheds.
~2000 people are bitten each year by Redback Spiders.
in addition, the Mouse Spider can give envenomation similar to the Funnel Web spider but bites are rare, and can be treated with Funnel web antivenom.
many other spiders can give bites and some can cause local pain, nausea, headaches, dizziness and vomiting.
some spider bites have been attributed to causing local tissue necrosis and perhaps chronic ulceration (“necrotising arachnidism”):
white tailed spider - although there is a lot of controversy as most bites do not result in long term sequelae
wolf spiders
Sac Spiders (Cheiracanthum species)
The Recluse or Fiddleback Spider is a deadly spider belonging to the genus Loxosceles. Recluse spiders are found in many parts of the world and have been introduced into Australia. The venom of this spider can cause severe skin necrosis (eating away of the flesh) and can be fatal although not many deaths have been recorded.