New Zealand weather radar picked up considerable echo over the Waikato region of the North Island on Thursday and Friday — but instead of a rainstorm, experts believe that all the activity could be chalked up to a huge mass of bugs.

"We’re not completely sure, but we strongly suspect the echo is swarms of insects," said New Zealand weather analysts MetService on their website, which has images of the odd swarm.

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"To show up in radar imagery like this, they must have some of the characteristics of precipitation particles: similar size, fairly numerous, enough water content (or perhaps coating)."

It's still unknown what exactly the supposed insects are, said Stuff.co.nz, although entomologists have come up with a few ideas: their guesses include a massive gathering of aphids, and a group of the beetle form of the pesty Tasmanian grass grub, which is known to swarm densely this time of year.

"It is the right time of year for them to emerge. They can come out in massive numbers," entomologist Stephen Pawson told Stuff.

The mystery insects are likely to fall into the ocean when they tire, added Stuff, meaning that surfers might want to tread with caution in the next couple of days.

In 2008, a swarm of insects over Queensland, Australia, almost triggered a storm warning after radar picked up signs of the gathering, said The Courier-Mail.