He said the bugs came about at 10.30pm, and the swarm had included some grasshoppers and cicadas.
"The heat is the trigger, plus the lights. They come out and there are just heaps of them.
Grass grub beetle part of a huge swarm that appeared in the Onekawa factory that Kerry Epplett works at two weeks ago. Photo / Kerry Epplett
"It's quite bad, they are really annoying just flying around all the time, mainly on the bench where you are working. They're harmless but there are just so many of them."
He said he had worked at the factory for more than four years and he had never seen swarms that size in previous years. But this wasn't even the first time he had seen a swarm that size this season.
"We had one a couple of weeks back too, around about the same amount. We beared with it, but we still had the big clean-up."
Local Mandy Denny took a picture of grass grub beetles swarming in Hastings on Thursday night.
Hawke's Bay Regional council Team Leader Principal Advisor Biosecurity Biodiversity Mark Mitchell said the hot muggy weather was bringing in more grass-hoppers, Tasmanian grass grubs, black field crickets and other bugs than usual.
"Between January and March these bugs are hatching, flying around and looking for homes."
He said we will continue to see the bugs in high numbers over the next few warm wet days, but the numbers should reduce when the weather cools down next week.
"The good news is they are relatively harmless, they like to eat dung, they don't live for very long, and they don't like cold weather."
A council spokesperson said they have had a couple of enquiries about bugs and advised people to turn off lights at night to avoid attracting insects, keep windows and doors shut where possible, and apply insect repellent sprays to entrance surfaces where appropriate.
Summer is typically the season for insect populations to explode nationwide, sometimes leading to indoor intrusions. Photo / Supplied
The Garden Depot Hastings employee Aimee Thorsen said people typically didn't look to exterminate grasshoppers, but they did come in sometimes to treat their lawns for grass grubs.
"It's getting a bit late to deal with that now - normally it would be done in spring when they are actual grubs, before they become a beetle that has already done the damage, although some people do still try."
She said the number of enquiries this season still seemed to be a normal amount for the time of year to her.
