Bogong moths arranged like roof tiles in their summer hideaway.

Bogong moths

Each spring bogong moths migrate from lowland breeding grounds to the high country in southeast Australia where they spend the summer.

• 2 January 2008 | Updated 14 October 2011

• Background
• Description
• Life history

Background

Each year as the weather warms in south east Australia, bogong moths (Agrotis infusa) prepare to migrate.

Through spring they fly to the high country of the Snowy Mountains in southern New South Wales and the Victorian Alps.

They have been doing this for thousands of years to escape the harsh summer environment in their winter breeding areas of the Darling Downs in Queensland, western slopes and plains in New South Wales and drier inland regions of Victoria.

In autumn they make the return journey.

Bogongs fly at night and, attracted to lights, can cause problems for floodlit buildings by blocking air-conditioning ducts and setting off alarms.

During the day they hide in dark crevices.

There are numerous reports of large groups of bogong moths causing inconvenience to humans.

In 1865, bogong moths invaded a church in Sydney, causing a service to be abandoned.

In Canberra in the mid-1970s, bogong moths invaded new, brightly lit building in huge numbers, causing lifts to fail.

In 1988, vast numbers of moths caused havoc at the newly completed permanent Parliament House and engineers had to reduce lighting and redesign air intakes.

Winds have been known to carry bogongs out to sea, even as far as New Zealand.

Description

While bogongs occur throughout non-tropical Australia, they only appear to migrate in the southeast.

Clustered like roof tiles, they sleep through the summer (aestivate) in caves and crevices at about 1 200 metres.

Bogong moths are brown with a wing span of about four centimetres. They belong to the family Noctuidae.

The wing pattern easily distinguishes the bogong moth from other closely related species. 

Their brown colouring provides camouflage while they are resting in the caves.

Life history

Adult bogongs feed on nectar and, during migration, are often seen feeding at dusk on flowers such as grevilleas.

They prepare for summer by building fat reserves (up to 60 per cent of their bodyweight).

During aestivation they usually do not feed but they may drink in dry weather.

Adults emerging in spring are sexually immature.

The food they eat when they return from the mountains allows them to reproduce.

If nectar is not available they are unable to reproduce.

In a favourable year a female lays up to 2 000 eggs and the larvae grow slowly over winter.

Known as cutworms, because they cut plants off at ground level, they can be minor pests for crops.

In late winter the larvae pupate in the ground.

Plague numbers only occur when there is favourable weather and abundant food.

Plagues are difficult to predict as the factors favouring reproduction also favour fungi and predators that attack the bogongs.

CSIRO Entomology is not currently researching bogong moths.

See more Australian moths in Australian moths online: a photo gallery.