"Lucky you're already in the underwear section," one woman added.
"Kudos for getting close enough for a photo. Those damn things can jump like an Olympic triple jumper," another wrote.
"I now understand the burning of the bras!" quipped one user, while others added the whole shop should be "burned to the ground".
Asked which store it was so other customers could "stay away", Harrison Pring said it was "lucky" Ballarat has more than one Kmart.
"That's how you know you're in Australia!" commented another member of the group.
It wasn't the only terrifying spider find in recent days, after NSW woman Christine Jones discovered an enormous spider hiding under the door handle of her car.
"Thought it was hairy caterpillars at first. Haven't used my car for a week," Ms Jones wrote in a post on the Australian Spider Identification Page on Facebook.
"Saw it at the last moment."