Experts said the spiders may be spinning the sticky webs to help them survive the deluge, which has forced thousands of people to leave their homes over the past week.
"What we've seen here is a type of wolf spider," said Owen Seeman, arachnid expert at Queensland Museum.
"They are trying to hide away [from the waters]."
The spider webs were seen near the inland city of Wagga Wagga in New South Wales, where 8 000 people were forced from their homes before the flood waters receded on Wednesday.
The Australian Museum's entomology collections manager Graham Milledge said the spiders' behaviour was known as ballooning, and was typical after spiders are forced to flee from floods.
"They often do it as a way of dispersing and getting into a new area," Milledge told the news.com.au website. "In an event like this, they are just trying to escape the floods."
Sydney's Taronga Zoo said Australia's spider population has boomed in the wet weather.