The unnamed driver was reversing her Kia van down a slipway next to a river in Kingston when, according to a police release, she spotted a spider in her lap.
She then dived out of the vehicle, allowing it to roll into the water.
The van floated briefly down the Etowah River before becoming "totally submerged," police said.
By the time a Georgia State Patrol officer arrived, there was no sign of the van.
The Atlanta Journal-Constitution newspaper reports that a passerby tried to help search in his boat, to no avail.
The woman's insurers plan to trawl for the van, reports AJC.
Most spiders found in Georgia are harmless but bites from two types, the Black Widow and the Brown Recluse, are highly poisonous.