A mother on the afternoon school run was given a nasty surprise when a brown snake suddenly popped its head out over the top of her windscreen.

Key points: The snake appeared during a drive to swimming lessons

The snake appeared during a drive to swimming lessons A school bus driver used a stick to remove it

A school bus driver used a stick to remove it Snakes are said to be common in the Rapid Bay area

Alisha Chaffey had just picked two of her children up from Rapid Bay Primary School, south of Adelaide, and was driving them to swimming lessons when the unwanted passenger revealed itself.

"I saw this little head come down and I just thought 'what am I going to do?'" she said.

"Once you're out of the township, the speed limit goes right up to 100 [kilometres per hour] and so I first thought if I can get out of town once I hit 100 [kph] it's going to go flying off.

"Then I thought 'but I'm in a ute and it's going to land in my tray and it's going to be really angry when I get to my next stop'."

The roof-riding reptile had wrapped itself around the aerial, and Ms Chaffey suspects it attached itself by descending from a tree branch near the school gate.

The snake is believed to have descended onto the car from a tree. ( Facebook: Alisha Chaffey )

Desperate for help Ms Chaffey, who also had her 18-month-old in the ute, drove back towards the school.

"I wasn't going to open any door or put my windows down or beep my horn. I didn't want to scare it," she said.

"I just waved my arms frantically until someone saw me looking crazy.

"The teacher that saw me went and got all the other teachers."

Photos 'freaked me out more'

Ms Chaffey said the driver of the local school bus used a long stick to delicately remove the snake.

"He just kind of hooked it onto the stick and put it on the ground and then they all stomped and made a lot of noise and scared it away," she said.

"I wasn't that scared. I knew it was a snake straightaway. I live on a farm, I'm from a farm … I'm from Darwin, I'm from the tropics. Tree snakes aren't uncommon.

"Seeing the pictures from the outside probably freaked me out more.

"With my little ones still in the car and the windows down, it could have been really, really scary."

The incident is not the first time a snake has been spotted close to the Rapid Bay Primary School.

Snake Catchers Adelaide manager Ange Broadstock said snakes are common in the area.

"In the last week or so, one of our crew had been down to Rapid Bay Primary School and did a snake awareness session," she said.

"They have so many snake sightings around their school."

Ms Broadstock said brown snakes generally were found on land, but were also known to climb trees.