The so-called "blister beetle" could be making a comeback in Wellington due to the warm summer weather.
An Australian native, the lax beetle, releases a toxin when crushed, which leaves welts or blisters on the skin.
The beetle was thought to be responsible for a rash of skin complaints among the city's residents last summer.
Entomologist Ruud Kleinpaste said the beetles were commonly found on the beach in the summer months where they live and feed off driftwood.
"When you come in contact with them and squash them a little bit, they tend to bleed a rather aggressive little bit of juice from their limbs and when that comes into contact with the skin, it can cause blisters," he said.
"They are attracted to nothing but their food source... but when they are flying (as adult beetles they have wings) and are sometimes confused by bright lights, so for instance if you have a bright light outside your house they are confused by it, fly around it and crash into it which I think is one of the ways they get near or into houses."
The toxin they leaked was their defence mechanism, Mr Kleinpaste said.
He advised anyone who had skin irritations from the beetles to get medical advice.
People who find them in their house should simply catch them with a jar and free them outside "while wishing them a happy life".