Bogong moth

Appearance

Adult bogong moths have an overall dark brown coloration, with a dark stripe interrupted by two light-colored spots on the wings distinguishing it from other moths. There are visual differences between the migratory and nonmigratory forms of the moth; migratory moths have brown hind wings while nonmigratory moths have paler hind wings.

Bogong moths have a wingspan ranging between 40–50 mm, and a body length of around 25–35 mm. The average weight of an adult bogong moth is 0.326 grams.

Bogong moth eggs are dome–shaped in appearance and are vertically ridged. They are 0.7 mm in diameter and 0.4 mm in height.

Caterpillars initially start out with a pale coloration, but as they grow and consume food they become green with pale and dark stripes and spots. Larvae achieve a maximum length of 50 mm.

Naming

The moth's name, "bogong", is derived from the Australian Aboriginal Dhudhuroa word "bugung", describing the brown coloration of the moth. It is an icon of Australian wildlife due to its historical role as an important food source and because aboriginal tribes would come to where the moths spend the summer to feast on them and hold intertribal gatherings. In recent years, it has become well known for its accidental invasion of major cities like Canberra, Melbourne, and Sydney due to strong winds during its spring migration.

Distribution

Bogong moth populations are primarily located across southern Australia, west of the Great Dividing Range. The regions contain populations of nonmigratory and migratory moths of this species, distinguished by their differing seasonal presences in each region.

The adult bogong moth lays eggs across New South Wales, southern Queensland, and northern parts of Victoria, where larvae hatch and grow until adulthood. During the spring season and subsequent summer aestivation, bogong moths migrate south or east towards the Australian Alps, and can be found in the Australian Capital Territory and Bogong Mountains. However, bogong moths can also be found in locations as far as Tasmania and New Zealand due to strong winds that blow them off their path.

Habitat

Bogong moth eggs and larvae are primarily found in self-mulching soils and crop pastures, where both wild and agricultural larval food sources are abundant during the autumn and winter seasons. The heavy presence of larvae in these pastures can lead to significant crop damage. During the spring and summer seasons, when grasses overtake these pastures, conditions are unfavorable for larval survival since larvae do not consume these plants. This leads to delayed breeding, as bogong moths are multivoltine and so can raise multiple generations. Instead, adult bogong moths migrate in a southerly direction during the summer and aestivate, until conditions are favorable again.

Food

Bogong moth larvae subsist on winter pasture crops and wild crop weeds such as cape weeds within bogong moth breeding grounds, primarily depending on annual dicotyledons that grow during the winter. Attacks on a wide variety of cultivated crops have been seen, with plants such as "Medicago" species, wheat, cabbages, cauliflowers, silver beet, peas, and potatoes all recorded being consumed by bogong moth caterpillars.

Predators

The bogong moth suffers from predation during both its migration and aestivation. During the spring and autumn migrations, several species of birds, mammals, and even fish have been recorded preying on the moth. Little raven, currawong and Richard's pipit congregations form to feast on bogong moths as they travel from aestivation sites during migration. Aboriginal tribes also traveled to aestivation sites to feast on the dormant moths, and may have searched for these bird congregations to locate these sites. Bats also attack the moths during active flight periods during the dusk, and foxes, bush rats, and dusky antechinus have been recorded eating moths. Of the mammals that prey on the bogong moth, the endangered mountain pygmy-possum is the most reliant on bogong moths as a source of food.

Migration

Bogong moths undergo whole scale long-distance migration biannually, in which they can travel up to 965 km. The spring migration begins in early September and occurs from the lowlands of Southern Australia south towards the Australian Alps for purposes of reaching aestivation sites. During the summer, the moths remain in their aestivation sites until autumn, when they migrate back towards the breeding grounds of the lowlands as early as February, but primarily in April. The bogong moth utilizes particular aestivation sites repeatedly throughout migrations, as seen with the development of parasites that depend on the regular arrival and departure of the moths from caves.