A Wellington mum is pointing the finger at an Australian beetle for causing clusters of welts and blisters on her son's skin yesterday.

Five-year-old Tom woke his parents about 5.30am on Tuesday complaining of pain on his arm, mother Jenna Limmer said.

She soon found several blisters on his torso and began "frantically googling" to see what might have caused them, but found nothing.

"In the morning when we all kind of surfaced and got up at seven, there were three more spots."

Advertisement

All up Tom had about 16 blisters across his body in patches, some appearing as small dots and others as large welts.

Some of the blisters were large welts while others were small spots, Jenna Limmer said. Photo / supplied
Some of the blisters were large welts while others were small spots, Jenna Limmer said. Photo / supplied

"I was like, 'oh crap, do I go to the hospital or do I go to the doctor?'"

Limmer took her son to the doctor, who could not explain the blisters.

She showed him a link a friend sent her about the spotted lax beetle, an Australian bug that is also found in New Zealand.

Other parents had posted on Facebook about the beetle, claiming it had caused blisters on their children.

She read that the fluid in the joints of the beetle causes blisters. The Manaaki Whenua – Landcare Research website has a page on the beetle, which says it can cause "skin inflammation".

"[The doctor said] 'Oh nah, I've never heard of it, I don't think so," Limmer said.

Another doctor and the on-call paediatric doctor at the hospital did not know what caused the blisters, and Tom was given antihistamines to take.

The doctor said there was a possibility Tom could have been bitten by sea lice at the beach and had a reaction.

But when Limmer returned home and stripped Tom's bed, she found the spotted lax beetle "mushed up" among the sheets.

Jenna Limmer found the 'mushed up' beetle in her son's bed yesterday. Photo / supplied
Jenna Limmer found the 'mushed up' beetle in her son's bed yesterday. Photo / supplied

"What we think happened is he's laid on it, and then has rolled around.

"We've seen those bugs heaps in our house ... I never thought anything of it. I usually just scoop it up and throw it outside."

Despite the uncomfortable blisters, Tom is doing well and has been playing with his siblings, she said.

"We just have to ride it out now."

Manaaki Whenua – Landcare Research entomologist arachnologist Grace Hall said the introduced Australian spotted lax blister beetle first came into the country in 1931.

Commonly known as the "blister beetle", it ranges in size from 12-15mm long and is found both within and north of Nelson.

They are common and widespread, breeding and laying their larvae in mangroves. The beetles cause blisters after coming into contact with humans, Hall said.

Regional Public Health has been contacted for comment.