Animal rescue officer Enola Evans found it in the bedroom window frame, and identified it as a harmless corn snake.
The charity said the reptile would be rehomed if its owner did not come forward.
“It’s not every day you get woken up by a snake trying to get into your bedroom through a window – the woman was terribly shocked,” Ms Evans said.
“By this time, there was no sign of the snake at the window, so the resident gave me permission to search her bedroom, in case it had come inside and hidden somewhere warm.
“But after thoroughly checking bed linen, and other possible hiding places in the bedroom, the snake was still nowhere to be found.
“As the window had been open for so long, it was getting quite chilly in there, so I decided to shut it. That’s when I spotted something moving.
“It was the snake, coiled around the window’s rim. He had been very well-hidden, so I was really pleased to find him.”
Corn snakes are a non-venomous breed sometimes kept as a pet.
The snake, which was captured on October 8, was moved into a carrier and taken to an expert boarding facility to be cared for until he could be reunited with his owner or put up for adoption.
Last year, the RSPCA received 1,219 reports about pet snakes in need of help, including many stray snakes.
A high number of calls came in during the summer months as snakes become more active during hot weather.
RSPCA scientific officer Evie Button said: “Snakes are excellent escape artists and will take the opportunity of a gap in an enclosure door, or a loose-fitting lid to make a break for it.”
Snake owners are urged to be vigilant, invest in an enclosure suitable for the species and make sure that enclosure is kept secure – and locked if necessary – when unattended.
