Dawud, 10, from Cornwall, was playing on the sand at Perranuthnoe, West Cornwall when the Portuguese-Man-of-War stung him on the sand.
His mum Yasmin collected the creature in a jar in case doctors needed to know what had caused the sting when she took him to hospital.
Dawud hopped to a nearby café to soak his swollen foot in water before paramedics arrived to help. After being checked over at West Cornwall Hospital, he headed home - taking his attacker with him.
"My children were playing by the waves and noticed this thing in the water," explains Yasmin. "They picked it up with a stick and it fell on my son's foot. He said it was like knives stabbing into him."
"It did swell up a little and there were some welts but thank God it wasn't any more serious. Dawud was intrigued by it and is really into wildlife and animals. It is luminescent and looks like an alien life form."
The jellyfish is still at home in the jar, but will eventually be buried in the family garden.
Keen wildlife fan Dawud reported his story to the Cornwall Wildlife Trust which monitors animal sightings in the region.