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Bogong moth

Bogong moth closeup

Moths. Some people are scared of moths; so many in fact, that the word "Mottephobia" was coined to describe this phobia. While you don't have to love them, moths, like everything alive, have their place in the world and this case study looks at one moth in particular - the Bogong moth.

Background

The Bogong moth is a night flying denizen of eastern and southern Australia. Its scientific name is  Agrotis infusa. The adult moth is about 30 mm in body length and has a wing span of about 40 to 50 mm. It is brown and beige in colour. Bogong moths can live in urban areas, forests and woodlands.

The Bogong moth life cycle is characterized by complete metamorphosis.  The diagram below shows the 4 different stages in a generalised moth life- cycle.

Eggs are small and laid in batches of up to 2000 on plants and soil. Hatching time is temperature dependent. The eggs hatch into small caterpillars.

The larval stage is commonly called a black cutworm. It feeds on cape weeds, and a variety of broad leaf plants. Once the larva has grown to a certain size, it sheds its outer skin which has become too small to contain its body. At each change, the body colour darkens.  It goes through this process several times, until it has reached its final size. When this happens, it produces a tough outer coating to protect itself as a pupa.

The pupa is attached to an inconspicuous place on soil or vegetation and remains motionless externally. The pupal stage last for about 4 weeks +, depending on temperature.  During this time, the tissues of the larval stage are completely reorganised to take on the shape of an adult e.g. antennae emerge, two sets of wings with scales form.

The adult forms exist on flower nectar while travelling but do not eat while they aestivate.

Services

The above could be the life story of many moths. What makes the Bogong special?

It migrates between  the eastern plains areas of Australia to the Australian Alps, seeking refuge from the summer heat. Using amazing navigational techniques, a moth flies by night and cover distances of up to 1,000km. In the Alps, it seeks out caves in which to aestivate, and  then after summer, it flies back to plains areas to breed where there is sufficient food for the larvae that will hatch from fertilised eggs. It does all this with a brain the size of a grain of rice. Scientists are investigating the mechanisms the moths use to perform this feat carried out in the darkness.

Culturally the Bogong moth is significant, both in prehistorical times and in modern day Australia.
Bogong moths were historically used as a food source by Aboriginal peoples located in South-eastern Australia. Groups would travel to the area towards the summits of mountains to harvest moths, where they also met with other Aboriginal peoples, fostering inter-tribal relations as people gathered and feasted during these harvests.They would go into the caves and scrape aestivating moths off the walls into nets and dishes using sticks. Once gathered, the moths would be roasted to remove the scales and wings and then either eaten immediately or ground into a paste and made into high protein "moth meat" cakes that would last and could be taken home. An excavation of Cloggs Cave, near Buchan in Victoria, revealed microscopic remains of moth on a small grinding stone, estimated to be about 2,000 years old. This is the first confirmed evidence of insect food remains discovered on a stone artefact in the whole world.1
In contemporary Australia, Bogong moths are iconic both because of the sheer numbers of them migrating. And also because of migrations gone awry. Strong winds and light pollution both can contribute to moths ending up in unexpected places e.g. the 2000 Olympic games in Sydney brought them notoriety. Also, because of its location, Parliament House in Canberra has hosted moth swarms on a number of occasions. They tend to cluster in crevices in buildings during the day and have been know to invade the interior of buildings.

In the past, the numbers of moths aggregating in  caves has been in the hundreds of millions. The density of huddled aestivating moths was estimated to be about 17, 000 moths per square metre of cave wall.  Around about 40 years ago, the numbers started declining. In the period 2017 - 2021, there has been a serious crash in numbers which has reduced the population to 0.5% of the previous years. In December 2021, the Bogong moth was added to the IUCN Red List as an Endangered Species.

Bogong moths have an important role to play in sustaining ecosystem integrity. (Remember the Jenga analogy.)

  • They provide  food for the Mountain pygmy possum,  antechinus, lizards,  frogs and spiders across the Snowy Mountain region. The loss of the moths is particularly devastating for the pygmy possums as they are just coming out of hibernation, and are in dire need of a bountiful, high quality energy source. Mountain pygmy possums are classified as critically endangered, with fewer than 2,000 left in the wild and their most urgent threat is now the loss of their spring food source, the Bogong Moth.
  • Bogongs are nectar-eaters, which makes them potentially important pollinators of native plants.
  • The remains of the moths have in the past contributed greatly to soil conditions in the alpine areas.

Summary of services provided for us

  • food web maintenance and ecosystem stability
  • information about unusual navigation skills
  • pollination services
  • traditional food with cultural benefits for Aboriginal people

Threats to the services?

IUCN threat to species scale
IUCN threat to species scale

As of 2021, the IUCN lists the Bogong moth as Endangered

  • Use of pesticides
  • Light pollution making navigation more difficult
  • Drought in feeding areas magnified by climate change
  • Scarcity due to land clearing of suitable nectar producing plants to support the migration flight

What can we do to retain these services?

Dig deeper

  1. 2000 Year-old Bogong moth (Agrotis infusa) Aboriginal food remains, Australia [↩]
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