He told Radio 6PR about the experience.
"It wasn't really a tickling sensation, obviously once the venom started to affect my skin it was a really burning sensation like a searing feeling," he said.
Mr Thomas said he believed the spider had burrowed into his abdomen on Friday night as he noticed a mark on his stomach on Saturday morning that continued to worsen.
Mr Thomas spent another day with the arachnid tunneling inside of him, before going to a hospital.
"Well after running tests and putting things inside my stomach they finally found out it was a tropical spider that's been living inside of me for the last 3 days, managed to get it out luckily," he told his Facebook friends.
Two doctors who initially assessed him "had no idea" what was causing the marks on Mr Thomas's skin until they called in a specialist dermatologist.
The spider was eventually removed with tweezers. It was dead when pulled out.
Mr Thomas said the experience had ruined his first trip to Bali.