A commonly found beetle that causes painful blistering to the skin could help explain some skin rashes that have left parents confused.
The spotted lax beetle has toxic chemical defences and when its excretions come into contact with human skin, it can cause severe skin inflammation.
Insect expert Ruud Kleinpaste says the beetles - which are also known as blister beetles - are fairly common across the country and excrete toxic chemicals when under threat.
The warning comes after a five-year-old Wellington boy was left with more than a dozen blisters across his body after falling asleep on top of the little-known beetle.
Jenna Limmer says her son Tom woke up yesterday complaining that he was sore and soon came up in 16 blisters across his torso.
She took him to the doctor, who was stumped as to what had happened.
Ms Limmer later went to change her son's bedding, worried that he was having an allergic reaction to it, when she found a crushed spotted lax beetle between the sheets.
The beetle, also known as parisopalpus nigronotatus (Boheman), was introduced from Australia in 1931 and has spread across the country north of Nelson.
Manaaki Whenua - Landcare Research says the 'blister beetle' ranges from 12-15mm long and is found within and north of Nelson.
"They are very common and widespread, breeding and laying their larvae in mangroves," it said.
"The beetles cause blisters after coming into contact with humans."
Ms Limmer took to Facebook to warn others about the dangers of the beetle.
A number of people have shared similar experiences, and many only realised what had happened to them after reading the post.
Wellington woman Nikki Alison discovered the insect in her toddler's bed and a blister on his inner thigh.
"He was complaining being uncomfortable in his car seat but I shrugged it off then when he woke up from his nap it was there... and within four hours had spread.
"We live in Kingston, Wellington and our house is completely riddled with them"
"If it wasn't for Jenna's post I would have never known what it was."