A couple has recalled the moment their six-year-old son saw rainbows, spoke gibberish and experienced seven seizures after suffering a rare allergic reaction.

Yarren was climbing trees at a park in Noosa Heads, Queensland, when he felt “a little woozy”.

“The boys were happily playing and Yarren ran up to my wife and said, ‘Mama, I can see rainbows on the inside’, and then he passed out,” his father Gregg told 9News. 

“He started having seizures, he bit his tongue and blood was pouring out,” mother Rachel said.

“And he had this rash that appeared on his stomach and it came all the way up to his throat.”

Yarren was rushed to Noosa Private Hospital and airlifted for further specialist care.

His parents feared for the worst. 

“My little boy’s laying there in an induced coma by now and we don’t have a clue what’s going on,” Gregg said. 

Doctors were left baffled and did not know what made him so sick. 

“We didn’t know what we were dealing with and we knew that his blood pressure was very low and his airway was compromised and he was having ongoing seizure activity,” LifeFlight’s Dr Hamish Brown said.

It was not until his family returned to the park two weeks later that they discovered what had caused Yarren’s symptoms.

“I couldn’t see any spiders, but I then looked underneath the tree and underneath was loaded with hairy caterpillars and their nests were,” he said.

Yarren had suffered a severe allergic reaction but, luckily, he recovered.

Two years on, he carries an Epi pen.

Anaphylactic reactions to the creatures are common but rarely this severe.