6 December 2022

Bogong moths are back - so should Parliament House be worried?

| James Coleman
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bogong moths

For years, bogong moths were the scourge of Parliament House. Photo: CSIRO, James Coleman.

For the past five years, the only bogong moth Canberrans have laid eyes on has taken the form of a pile of orange sheet metal on Drakeford Drive in Kambah, or maybe the decidedly more moth-shaped sculptures on the Acton Peninsula.

But that could be about to change. Recent numbers suggest the endangered species is bouncing back.

Until recently, the biannual migration of the bogong moth (Agrotis infusa) from the plains of Queensland, NSW and Victoria to the cool caves of the Australian Alps annoyed home and building owners across the eastern seaboard. Parliament House was even forced to switch its lights off at night to avoid people being swarmed.

Josh Coates from the Australian National University (ANU) has been studying the bogong for his PhD thesis, alongside Dr Peter Caley, who visits their known haunt at the ACT’s second highest mountain, Mount Gingera, every two weeks to record numbers.

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Josh says the population has been on a “steady decline” since the 1980s, but really took a turn in 2017 when drought arrived.

“There was hardly a bogong moth to be seen.”

The moth was veering towards the brink of extinction, with flow-on effects for its chief predator, the mountain pygmy possum. This nocturnal marsupial was already on the endangered list but moved into the critically endangered category, one notch below extinct in the wild.

But the indication from this year’s data points to a “positive response on previous years”.

“Last year, the numbers were up a little bit on 2020, but less than we expected, but throughout the estimation period this year, the numbers suggest the moths are back to pre-drought levels,” Josh says.

bogong moth

The bogong moth: ‘back to pre-drought levels’. Photo: Donald Hobern.

As with the explosion of almost everything at the moment, it’s down to the sopping wet weather.

“It makes sense that the recovery is due to the rainfall and more feeding resources for larvae,” Josh says.

“It’ still early days in the season but at this stage, it’s definitely promising.”

But someone may not be happy.

In 2005, Bill McCormick from the Science, Technology, Environment and Resources Section of Parliamentary Services wrote a paper entitled simply ‘Bogong moths and Parliament House’. Over 13 pages, he goes on to describe – in detail – the hell rained down by the pesky insects from the year the building opened in 1988.

“Starting in early October, the bogong moths start congregating around Parliament House,” Bill wrote.

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“Over the weeks, the warmer weather brings larger numbers of bogong moths through Canberra, joining those attracted earlier. The moths mass in the nooks and overhangs of windows and courtyards … enter [the building] through open doors … cannot find their way out and die.”

The moths even got into the air-conditioning vents and turned up in offices throughout the building. The carcases became a food and breeding source for carpet beetles and clothes moths, in turn causing infestations of those pests and “resulting in significant damage to fabric in the House of Representatives”.

It seems Canberra sits directly on the flight path of the moths as they travel south from the high peaks of the Brindabella Mountains. Parliament House was not only one of the highest objects in the area, but just in case the moths missed it, it was also lit up like the proverbial.

“It acts like a giant light trap,” Bill mused.

bogong moth

Bogong moth population numbers. Image: Dr Peter Caley.

It’s unknown exactly what effect artificial light has on moths, but the effect is clear. Check your own outside light on a summer’s night for details.

In desperation, the Parliamentary Services staff turned to CSIRO for help and the scientists suggested dousing the lights for a couple of nights.

So on 16 October, 1990, the then acting speaker advised members that pelmet lighting in offices in both the Senate and the House of Representatives would be turned off.

“Secondly, two of the four flagpole lights have been turned off. Thirdly, attendants have been asked to turn off all unnecessary office and suite lighting. Fourthly, a great number of external lights have been turned off, including ramp lights, lighting around the tennis courts and in the formal gardens.”

Even the street lights on Parliament Drive went out. And members were told to turn their office lights off when they left and not leave doors open.

“I assure the House that every action is being taken to contain bogong moth infestations,” the speaker said.

On the plus side, the effect of these measures meant the bogong moths saved taxpayers $365 a week (or $19,000 per annum) in energy costs.

The Department of Parliamentary Services was contacted for comment.

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