The Ministry of Primary Industries wants Kiwis to be on the lookout after a woman near the Auckland-Waikato border discovered a bug-spawning, colour-changing substance on her ceiling.
The woman posted a photo of the substance, which looks like a brown smudge with hundreds of tiny black worms hatching from it, to Reddit.
"What is this/these? It showed up on my ceiling beam so I left it there for 'observation'. It seemed to be made up of fibres. This morning I woke up and it has 'hatched' so I will get rid of it. But does anyone know what these are?" she wrote.
Reddit users responded with a mixture of amusement and horror.
"With the supermarket prices that's free lunch," one person wrote, while another described it as "Satan‘s work".
The woman told Newshub she originally thought it was some kind of ootheca - a type of egg case for creepy crawlies.
"But after standing up and investigating a little it was more of a flat, slightly raised plaque with a fine, felt-like appearance."
The Reddit user said the worms were "different to any I’d seen before or what I could find online" so she left them on the ceiling to observe.
"Over the week it became darker in colour, until I woke up a few days ago and saw that it had 'hatched,'" she said. "Hundreds of tiny black worms had come out."
The Ministry for Primary Industries (MPI) told Newshub from the information provided to them, they believe the bugs are armyworms.
"We suspect it is an armyworm (Spodoptera sp.) egg mass. These particular egg masses are laid by a moth from one of the armyworm species present in New Zealand," Biosecurity New Zealand plant health manager Nick Ward said.
Ward said if Kiwis come across similar unwelcome visitors, they should collect a sample and call the MPI hotline.
"There are a number of armyworm species present in New Zealand and we would need a sample of the larvae or egg mass to be able to determine exactly which species," Ward told Newshub.
"Armyworm moths are usually nocturnal and can find their way inside and through open doors and windows.
"If people do find a similar egg mass or emerging larvae, they should capture a sample in a container and call our exotic pests and diseases hotline (0800 80 99 66) or report via our online reporting tool https://report.mpi.govt.nz/pest/ and one of our specialist entomologists will be able to identify what species it is."
MPI said there are several armyworm species present in New Zealand but they have recently been discovered on corn cobs.
"The recent isolated discoveries - on maize and corn crops - of fall armyworm in five regions is new," MPI said.
"We have been encouraging farmers and growers – particularly those with maize and corn crops or regrowth crops to look out for signs of this plant pest and report and send us any samples so we can identify which species it is."