If you have been visited by a black beetle or two in the night recently, you are not alone.

Key points: Cockchafer beetles have all emerged at once, meaning they are appearing in plaque proportions

Cockchafer beetles have all emerged at once, meaning they are appearing in plaque proportions The recent wet weather in Tasmania has been a factor in their appearance

The recent wet weather in Tasmania has been a factor in their appearance The only purpose of the male cockchafer beetle is to mate and die

Blackheaded cockchafers have made the most of favourable weather conditions and have appeared in houses around Tasmania, in some cases in plague proportions.

Dr Simon Grove, senior curator of invertebrate zoology at the Tasmanian Museum and Art Gallery, said the beetles were found throughout south-east Australia.

He said while the beetles' presence was not unusual, their numbers were.

"They've all emerged at the same time," Dr Grove said.

Loading

A video from Brighton resident Alan Percy showed thousands of beetles in his house.

"Somewhere like Brighton would be a classic place for it because it's still suburban but surrounded by paddocks," Dr Grove said.

"[Beetles] benefited from European settlement because they like open grasslands.

"They do well in suburbia and on the fringe because the grasslands they like are well-cropped and a bit weedy."

Favourable weather

Dr Grove said the wet weather about a week ago would have been a factor in the beetles appearance.

"We've had so little rain, and that was their cue to get out and start mating," he said.

He said wet weather meant females could burrow back down into the soil while it was still moist.

"If it's rock hard again they can't burrow down and can't continue the life cycle," he said.

Dr Grove said blackheaded cockchafer larvae lived underground and fed on grass.

In the early stages, the larvae provide soil aeration, but then go through a hungry teenage stage feasting on lawns.

"If your lawn is looking really scrappy, and you've got weeds and no grass, then you could suspect these guys have been at work underground," he said.

"They like introduced grass."

As adults, their mission was to breed and die and their lifespan was short.

"The only purpose of the adult is to mate," Dr Grove said.

The beetles, which are attracted to light, are not harmful and also delicious to birds. ( Supplied: AP Min )

Beetles a 'bonanza for birds'

The good news is that the beetles, which are a scarab beetle in the dung beetle family, cannot bite.

Other than being a nuisance, the beetles are not harmful.

Dr Grove suggests collecting the cockchafers and putting them outside where a chook or bird would enjoy eating them.

"They are a great food for the birds; the birds will be having a bonanza," he said.

As to why the beetles come inside, Dr Grove said light confused them.

"The main idea is that it's a maladaptation to navigating by either the stars or the moon," he said.

"They end up flying towards the light and get hopelessly attracted."

And as for the unusual name? The name 'cockchafer' comes from 'chafer', as in the old English word for beetle, and cock, means big.