The non-native corn snake was spotted by a "shocked" council worker as he sorted through the rubble in a remote area off Mill Lane in Setchey, Norfolk.
It is now being cared for at the RSPCA's East Winch centre.
Manager Alison Charles said "abandoning" the snake was a "callous way to treat a pet".
Tim Borodka, who found the reptile on Friday, said: "It gave me quite a shock when I suddenly saw the snake slither away from me.
"I have come across lizards and wild grass snakes before, but nothing like this."
Ms Charles said the snake would have been unlikely to survive in the wild if Mr Borodka had not put it in a box and taken it to the King's Lynn rescue centre.
"The snake was found so far from any homes and amongst fly-tipped rubbish so it seems likely that it was abandoned."
Corn snakes are native to parts of North America and can grow up to 6ft (1.8m). The 3ft (0.9m) snake that slithered past Mr Borodka will eventually be rehomed at a specialist centre.
"We would encourage people who are thinking about taking on an exotic pet to research the needs of the particular species thoroughly and ensure they can meet them at all times," Ms Charles added.
Last year the RSPCA was called in to collect 807 exotic pet snakes. More than 450 of these were thought to be former pets that had either escaped or been deliberately dumped or released.
An exotic snake had a lucky escape after apparently being fly-tipped at the side of a road with a pile of kitchen cupboards.