Simon Charles Marsden, 37, admitted causing unnecessary suffering to a protected animal when he appeared at Mansfield Magistrates Court on Thursday.
RSPCA officers were called to Marsden’s Carlton Road home, on June 19, after neighbours complained about a barking dog.
They followed a strong smell to the third floor where the bodies of 20 royal python snakes were found in clear transparent boxes, said David Payne, for the RSPCA.
When they returned later, the carcasses had been disposed of, he said, so no post mortems could be carried out.
A vet’s report was read out in court: “Allowing animals to die a horrible death from asphyxiation is not acceptable.
“We have no idea what the pathogen was. Perhaps it was a completely treatable infection curable by antibiotics.”
In a police interview Marsden said he bought a new snake in November 2015, which may have been infected.
He said he had fed and cleaned them regularly, but then some of them began to make “wheezing noises”.
“It happened quite quickly,” he said. “They just started failing. I did my best for them. I read that it normally leads to death. It distresses me something chronic.
“I am very upset about what happened. I should have done things differently. I should have asked for help but I am not one to ask for help.”
Between December 2015 and March 2016, 25 snakes died and Marsden didn’t contact a vet.
The court heard that the property was in a “poor state of repair” with the heating on, but wind was blowing through broken windows in the room where the pythons were kept.
Marsden, and his partner also owned a dog, a blue Macaw parrot and a black cat, which were found “in a resonable condition.”
Simon Greaves, mitigating, said Marsden had looked after snakes since he was a young man with no problems, but he had been ill.
“He has not put a foot wrong for many years. He found himself taken aback by a period of profound ill health.”
He said Marsden, a supermarket delivery driver, was “careful and caring for many years.”
Sentencing was adjourned until the afternoon of December 22 for probation reports.