The 28 year-old suffered severe burns after attacking the arachnid with an aerosol can at his home in Clacton in Essex.
The man was summoned by his wife to deal with a spider she had seen scuttling behind the lavatory on Bank Holiday Monday. Not being able to reach it, the man decided to kill it by spraying it with the can.
However he was unable to see whether it was dead because the bulb in the bathroom light had blown. At this point he turned to a cigarette lighter to illuminate the room, but in the process ignited the gas fumes and caused an explosion.
The blast was so strong it blew the man off his feet and lifted the loft door off its hinges.
He suffered flash burns to his head, legs and torso and was rushed by ambulance to hospital after dousing himself in cold water.