Bogong Moth

No website about the Australian Alps would be complete without a piece on the Bogong Moth.

Attached below is a great overview taken from the ABC Science website (from 2002).

Bogongs migrate south

Image: CSIRO

Bogong moths migrate up to a thousand kilometres to find a cool summer home in Australia’s southern alps, where they are a crucial source of food for the local wildlife. Despite this amazing journey, very little is known about their basic biology.

By Abbie Thomas

Early summer barbeques along the east coast of Australia wouldn’t be the same without a visit from one of our most amazing insects. Bogong Moths, Agrostis infusa, migrate over 1000km each year from the black soil plains of Queensland and western NSW to the Australian Alps, seeking refuge from the summer heat. Along the way, they travel by night and then in the morning, drop down to the ground to rest in the shade during the day.

Bogong moths have a wingspan of about 50mm, and can be recognised by their dark brown mottles and two light spots on each wing.

Moth city

At night, the lights from towns, fires and other human activities attract the moths and they can become quite a nuisance. A Bogong moth even starred in the closing ceremony of the Sydney 2000 Olympics, when it perched on opera singer Yvonne Kenny during her performance.

Every year, migrating moths find their way into Canberra’s Parliament House, squeezing through air-conditioning ducts and sometimes winding up in the Chamber itself. There’s even the Bogong Moth Motel at Mt Beauty, near where the insects come to stay in the Southern Alps.

As the moths migrate southwards, their world collides with human society. Their route, followed for thousands of generations past, now passes over the bright lights of Canberra and other large cities. The lights fool the moths into behaving as if the sun is coming up. Their natural response is to dive down to the ground to find a dark place before the heat of the day sets in, and suddenly there are moths everywhere.

Buildings can become covered with a thick coating of moths, desperately seeking dark cracks and crevasses to hide from the sun. Their need to escape the heat has driven these moths to evolve one of the most amazing migration strategies of any Australian animal.

KEY FACTS

When: Bogong moths fly south from Queensland every spring to wait out the heat of summer in alpine caves. They return in autumn to Queensland to mate. The Ngan Girra Festival (formerly the Bogong Moth Festival) is held on the last Saturday in November, 2002.

Where: Darling Downs, Queensland, and the Bogong Plains, Victoria ( near the town of Mt Beauty). The moth’s breeding grounds stretch from inland southern Queensland and northern NSW right down to the Hay plains.

Other info: Bogong moth facts:
1.Bogongs live only a year, but travel over 1500 km during this time.
2.There is a carpet of dead moth bodies 1.5 metres thick on the floor of some Alpine caves, built up from thousands of generations.
3.Canberra lies directly in the path of the migrating Bogongs and the bright lights create big problems for moth navigation.

Beating the heat

Over 50 years ago the secret life of the Bogong moth was revealed by one of Australia’s great entomologists, Ian Common. He published a paper in a 1954 issue of Australian Journal of Zoology, announcing that Bogongs migrated from Queensland to the Australian Alps each spring. Until then their breeding grounds had been a mystery.

Bogong moths hatch in early spring as cutworm caterpillars, and begin feeding on the grasses and crops of the Darling Downs in Queensland. They bury themselves and pupate, emerging as moths three weeks later. Ravenously they gorge themselves on flowers by night and shelter from the heat during the day.

As the summer storms begin to build, the barometric pressure drops, telling the moths it is time to head south. In their tens of millions, they travel up to several hundred kilometres each night, feeding on flowering gum trees as they go. Winds and storms along the way can blow them as far off course as New Zealand and Melbourne.

Some time in November, the moths arrive in the Alps and head straight for the dark cool crevasses of the rocky caves scattered throughout the Bogong Plains, near Mount Bogong in Bogong National Park. Up to 17,000 moths per square metre will pack themselves along the walls of the caves.

The moths remain in these cool caves all throughout the summer. Every once in a while, they flutter out of the cave in the evening for a few hours, then flee back to the shelter again. While they have avoided the danger of hot days, they are still killed in their millions by the local wildlife, who look upon the arrival of the moths as a giant feasting opportunity. Antechinus, spiders, lizards and the Mountain Pygmy Possums all gorge themselves on the fatty bodies of the moths.

Ancient feast

In the past, Aboriginal people gathered in the area to take advantage of the temporary food bonanza. Diann Witney from Charles Sturt University says people from many different tribes would come together to carry out business and hold ceremonies. The moths provided a novel source of food. Some accounts say that moths were roasted in hot ashes to burn off the wings and legs, then mashed into “moth meat”, which had a nutty taste like walnuts.

Bogong moth damper

Before arsenic found its way into the moths, they made a fine dinner. Here’s a modern adaptation of an ancient recipe.

A generous handful of moths
1 cup plain flour
1 cup self-raising flour
1 cup powdered milk
1/4 teaspoon raising agent
water

Using a mortar and pestle (or near equivalent) pound up the moths with the powdered milk. Mix in the remaining dry ingredients. Add sufficient water to make a stiff dough and shape into a ball. Flatten the ball to a height of 2.5 centimetres, lightly flour the surface and cook in ash, camp oven, or domestic oven until cooked through. Serve hot.

Recipe courtesy of Vic Cherikoff

A festival to celebrate the arrival of the moths is still held today, near Albury at Mungabareena Reserve. Held on the last Saturday in November, the festival features Indigenous performers, spear and boomerang throwing competitions, bush tucker and indigenous kids activities. A few years ago, the name was changed from Bogong Moth Festival to the Ngan Girra Festival (which means “gathering place”). Up to 5000 people – both locals and overseas visitors – come to the festival each year.

The moths don’t just feed people, they are also an essential part of the Alpine ecosystem. Bogong moth expert Ken Green from the NSW National Parks and Wildlife Service says bogongs are the second biggest ‘energy input’ into the mountains, after sunlight. The animals that benefit include ravens, pippets, robins, many reptiles, fish, the marsupial rat Antichinus and of course the mountain pygmy possum.

Disturbingly, in the past few years, Ken has noticed patches of dead grass below caves where moths were sheltering. Analysis revealed it to be arsenic, which moths are carrying into the alpine area in their bodies. The source at this stage is still unknown, but could possibly be from residual agricultural chemicals, still present in the ground where the moth larvae develop.

The long trip home

At the end of summer the moths must prepare for the long trip back to Queensland where they will mate, and then die. Many have not survived their stay in the mountains, or been eaten by predators. The few who flutter back home in February and March don’t have anywhere near the visibility of the thick swarms which headed south in November.

Perhaps one in 1000 moths will make it all the way back home, feeding on nectar along the way to keep their energy up. As soon as they arrive back, seven months after crawling out of the ground, they mate and the female lays up to 2000 eggs. So begins the cycle once more.

Mystery moths

Mr Ted Edwards who is a fellow with CSIRO Entomology says that although the moths are so easy to see in their millions during their mass migration, surprisingly little is known about them. For example, no-one knows what their conservation status is. This is made more difficult by a lack of data on how many moths there were before the 20th century. The populations vary so much from year to year that only a very long term study could tease out any trends, and this is not being done, Mr Edwards says.

There are many questions left to be answered about the bogong: why do the moths travel so far to avoid the hot weather? Why do they sometimes leave the shelter of their caves? How much of an impact are humans having on their population?

There are growing pressures on the moth. As caterpillars, the bogong is a crop pest, and millions are killed each year by pesticides. Perhaps the biggest unknown is the long term impacts of brightly lit cities on the moths’ ability to stick to their migration route.

Further info and credits

Bogong moth biology

The Moth Hunters J. Flood, 1974, ANU, Canberra.

Shedding Light on Lepidoptera in Ecos magazine, April 1999, p:33

Special thanks to:
Diann Witney, Charles Sturt University
Mr Ted Edwards, CSIRO Entymology
Photographs courtesy of CSIRO

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