The iconic colourful beetles that herald the festive season in Australia have had their populations decimated over the past few years by bushfires, drought and a loss of habitat.

But Dr David Yeates, director of the Australian National Insect Collection at the CSIRO, is expecting the beetles to emerge soon after a wet and warm spring.

"Usually if there are good numbers of Christmas beetles you can see them feeding on the gum leaves and often their dead bodies can be found underneath gum trees after they've been feeding," he said.

Drought had compacted the soil in which the beetle larvae lived, making it more difficult for them to feed and eventually emerge as adults.

"They have to dig up out of the soil and if it's very hard and impacted and dry that can be challenging for them," Dr Yeates said.

ANU entomologist Paul Cooper said given the wet spring he couldn't see the soil being too hard as it had been in recent years.

"Anything that has been living underground hasn't been able to come out for a few years. That doesn't mean they die - they can live for quite some time underground in their pupal form. Therefore once the rain hits they can emerge," he said.

Insect population booms at the beginning of summer were common, but a particularly wet and warm spring had created the perfect condition to bring our six-legged friends out in droves.

"Insects are cold-blooded like other invertebrates and they respond to the temperature and day length increasing in spring, so there's always an increase at this time of year," Dr Yeates said.

Mr Cooper said cicada populations usually didn't emerge till late December or early January, so the cacophony of the bugs Canberrans were hearing was a promising sign.

The ACT experienced its wettest spring in 10 years, receiving 267mm of rainfall over the month and 13 separate days with more than 10mm - the most since the spring of 1974.

Above-average spring temperatures, including abnormally warm nights, had provided insects with an optimal breeding ground for the run into summer.

"The humidity always helps small animals like invertebrates survive better because the struggle they have in quite a dry climate like Canberra is keeping moisture in their bodies and reducing their water stress," Dr Yeates said.

"[This year] is a similar phenomenon to what happened after the Millennium drought. There were a couple of nice wet years and a flush of insects and other invertebrate numbers following that extended dry period."

Another local favourite returning after some years absent was the bogong moth.

Bogong moths were commonly found in droves in the Brindabellas, but their populations had dropped off as drought hit New South Wales and southern Queensland, where their caterpillar larvae hatched and grew.

"When there's drought in that country there's less vegetation and less plants for the caterpillars to feed on but we're happy to report that with the rains there's been an uptick in the numbers of Bogong moths up in the high country," Dr Yeates said.