Residents in Victoria's Gippsland region say the gossamer-like veils appeared after days of heavy rain.
In one area, a spider web covered more than a kilometre along a road.
Experts say the veils are created by a survival tactic known as "ballooning", where spiders throw out silk to climb to higher ground.
Dr Ken Walker, a senior insects curator from Museums Victoria, said it was likely that millions of spiders had thrown strands up to the surrounding trees.
"Ground-dwelling spiders need to get off the ground very quickly.
