Dr Lambkin said the creatures, drawn towards bright light at night, had increased in number because of the wet season but were now trying to find new habitat after the water started to dry up. “People are noticing them because they've been attracted to light, so most people who are seeing them are actually seeing them on the ground, dead or dying, either in pools or under street lights,” Dr Lambkin said. “They're obviously on the move. They're in unusual numbers – that is the difference. This is not an enquiry we get every year and we think it's because of the floods. “It is definitely a significant increase, now this is from Maroochydore right down to the Gold Coast we're getting reports of them. I was in Mt Isa and there would have been hundreds there around the lights in Mt Isa about 10 days ago. “And there are reports of bucketloads out of pools and things like that, so it is very much a significant increase in the numbers.”

A Tarragindi resident said she had noticed the beetles ramming into windows at her home. “They're noisy buggers, they just smash into the glass,” she said. They have also been seen at the Goodwill Bridge and in parts of the CBD, including the Queen Street Mall and the walkway near the Cenotaph and Post Office Square. The beetles were also out in large numbers when the Lions took on the Dockers under bright lights at the Gabba last Saturday night. Thousands of the creatures were scattered along the concrete concourse where fans walked as they left the grounds. Dr Lambkin said the diving beetles were “quite strong” and were able to fly for “many kilometres”.

“If we set up a light trap, this would be one of the groups, if there's any water within about three kilometres, four kilometres, these guys will turn up,” she said. “I suspect that what's happening is they're moving through and they're not finding their habitats, and that's what we're getting the reports of, the numbers found are dead. They haven't managed to repopulate and complete their lifecycle. “They really need to get into freshwater, clear freshwater as much as possible, so the Brisbane River's not going to do it, not at the moment.” She said insect populations were prone to “boom and bust” cycles. It would be pointless spraying them as they were not pests and would not live for a long period anyway when out of freshwater, Dr Lambkin said.

Dr Bronwen Cribb, from the University of Queensland's School of Biological Sciences, said the spike in insect numbers was not a surprise given the big wet season the region had endured. “It might not be a good season for us but it's a good season for them,” she said. Griffith University entomologist Professor Clyde Wild said the water beetles had been given “huge opportunities” to breed but conditions were now drying up. “They're water beetles so they live in mild conditions and as a consequence if they're left out in the sun getting cooked they'll die very quickly,” he said. “Most beetles have good hiding capabilities and they'll find some shade or something. These things don't have that capability because they normally live in water where they don't get cooked.”

Professor Wild said the beetles may be a nuisance for a while but they would soon disappear. “If we get a normal summer next year, they'll be uncommon. If we get another set of floods, we'll have another flood of beetles to follow at another time.” Experts dismissed suggestions by a resident who saw the beetles that they may be exploding, although Professor Wild said they had a tight shell and if they died in the sun and swelled up “they might perhaps pop”.