Bogong moth
Template:Short description Template:Use dmy dates Template:Good article Template:Use Australian English Template:Speciesbox The bogong moth (Agrotis infusa) is a temperate species of night-flying moth, notable for its biannual long-distance seasonal migrations towards and from the Australian Alps, similar to the diurnal monarch butterfly.<ref name=":0">Template:Cite journal</ref> During the autumn and winter it is found in southern Queensland, western New South Wales, western Victoria,<ref name=":1">Template:Cite journal</ref> and also in South and Western Australia.<ref name=":4"/> Adult bogong moths breed and larvae hatch during this period, consuming winter pasture plants during their growth.<ref name=":1" /> During the spring, the moths migrate south or east and reside in mountains such as Mount Bogong, where they gregariously aestivate over the summer until their return towards breeding grounds again in the autumn.<ref name=":0" />
The moth's name, bogong, is derived from an Australian Aboriginal language; the Dhudhuroa word bugung describes the brown colouration of the moth.<ref name="vicnames1">Template:Cite web</ref> It is an icon of Australian wildlife due to its historical role as an important food source and because Aboriginal peoples would come to where the moths spend the summer to feast on them and hold intertribal gatherings.<ref name=":1" /> In recent years, it has invaded major cities like Canberra, Melbourne, and Sydney due to strong winds during its spring migration.<ref name=":4">Template:Cite web</ref>
Starting around 1980 and accelerating rapidly after 2016, the Bogong Moth population has sharply declined as a result of increasingly severe droughts, along with increased temperatures in caves used by the moths for aestivation, both primarily resulting from anthropogenic climate change. In December 2021 the bogong moth was added to the IUCN Red List as an Endangered Species.<ref name=abcredlist/>
Taxonomy and etymology
Bogong moths was first described by French lepidopterist Jean Baptiste Boisduval in 1832, who described the moth as Noctua infusa from a type specimen from Australia.<ref name=":0" /> He described the moth as having blackish-brown hind wings.<ref name=":0" /> However, in 1903 British entomologist George Hampson classified a specimen with white hind wings under this name, alongside another specimen of Agrotis spina with blackish-brown hind wings.<ref name=":0" /> Australian amateur entomologist Alfred Jefferis Turner identified A. spina as a synonym of A. infusa in 1920.<ref name=":0" /> I. F. B. Common, an Australian entomologist, found specimens with both hind wing colours in 1954. Specimens with the white hind wings were only found during specific months in mercury vapour light traps near Canberra, and he attributed the white hind wing specimens to a seasonal form.<ref name=":0" />
The moth's name, bogong, is derived from the Dhudhuroa word bugung, meaning brown moth.<ref name="vicnames2">Template:Cite web</ref> Its presence has contributed to the naming of numerous locations and landmarks. For example, a town, Bogong, in the Australian state of Victoria has been named after the moth.<ref name="boogong_moth">Physical Map of Australia, special advertising feature of Australia.com on pg 16, National Geographic magazine, May 2006, Washington DC</ref> Mount Bogong, located south of the Bogong High Plains, is also named after the moth, with its traditional name, Warkwoolowler, meaning the mountain where Aboriginal people collected the "boo.gong fly".<ref name="vicnames1" /> The Taungurung name for the bogong moth is debera.<ref>Template:Cite book</ref>
In the Australian state of New South Wales, a series of mountains in the Kosciuszko National Park are named the Bogong Peaks.<ref name="pb1">Template:Cite peakbagger</ref>
Description
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Adult bogong moths have an overall dark brown colouration, with a dark stripe interrupted by two light-coloured spots on the wings, distinguishing it from other moths.<ref name=":7">Template:Cite book</ref><ref name=":1" /> 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.<ref name=":0" /> Bogong moths have a wingspan ranging between 40–50 mm (1.6-2.0 in), and a body length of around 25–35 mm (1-1.4 in).<ref name=":8" /><ref name=":1" /> The average weight of an adult bogong moth is 0.326 grams.<ref name=":2">Template:Cite journal</ref>
Bogong moth eggs are dome–shaped in appearance and are vertically ridged.<ref name=":8">Template:Cite book</ref> They are 0.7 mm (0.03 in) in diameter and 0.4 mm (0.02 in) in height.<ref name=":8" />
Caterpillars initially start out with a pale colouration, but as they grow and consume food they become green with pale and dark stripes and spots.<ref name=":7" /> Larvae achieve a maximum length of 50 mm (2.0 in).<ref name=":8" />
Distribution and habitat
Bogong moth populations are primarily located across southern Australia, west of the Great Dividing Range.<ref name=":4" /> The regions contain populations of nonmigratory and migratory moths of this species, distinguished by their differing seasonal presences in each region.<ref name=":1" /> The adult bogong moth lays eggs across New South Wales, southern Queensland, and northern parts of Victoria, where larvae hatch and grow until adulthood.<ref name=":0" /> 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.<ref name=":0" /> 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.<ref name=":10">Template:Cite journal</ref><ref name=":1" />
Breeding grounds
Bogong moth eggs and larvae are primarily found in self-mulching soils (soil that mixes itself) and crop pastures, where both wild and agricultural larval food sources are abundant during the autumn and winter seasons.<ref name=":0" /><ref name=":1" /> The heavy presence of larvae in these pastures can lead to significant crop damage.<ref name=":0" /> During the spring and summer seasons, when grasses overtake these pastures, conditions are unfavourable for larval survival since larvae do not consume these plants.<ref name=":1" /> This leads to delayed breeding, as bogong moths are multivoltine and so can raise multiple generations.<ref name=":0" /> Instead, adult bogong moths migrate in a southerly direction during the summer and aestivate (remain dormant), until conditions are favourable again.<ref name=":1" />
Aestivation sites
During the spring migration, adult bogong moths can be found in their ideal aestivation sites, which generally consist of cool, dark caves and crevices but can include spaces underneath tors and even fallen tree trunks.<ref name=":5">Template:Cite journal</ref><ref name=":0" /> Stable temperatures and humidity make these locations ideal for bogong moth aestivation. Crevices regulate their environment through wind flow, and caves generally have more regular temperatures and greater humidity.<ref name=":5" /> This reduces water loss in bogong moths during their inactivity.<ref name=":0" /> While temporary sites can be used in lower elevations, these sites undergo massive population fluctuations and movements throughout their use.<ref name=":0" /> Permanent aestivation sites are generally found in higher altitudes of 1500 metres (4920 ft) or above, with the largest, most stable aggregations found on the summits of mountains such as Mt. Gingera.<ref name=":5" /><ref name=":0" />
Life cycle
Adult bogong moths lay up to 2000 eggs in the soil or on plants near the soil after returning from aestivation sites in the autumn migration.<ref name=":1" /> Incubation times vary depending on temperature, with eggs hatching after a period of 4–7 days in laboratory conditions.<ref name=":0" /> The larvae of bogong moths undergo six instars.<ref name=":1" /> Caterpillars grow slowly throughout the first three instars, taking until June to develop over the winter.<ref name=":1" /> However, the larvae go through fast growth during the spring, reaching the final instar in late August to September, soon before migration.<ref name=":1" /><ref name=":0" /> They are active at night, when they feed on plants within breeding grounds.<ref name=":7" /> Larvae undergo pupation in soil chambers at a depth of 20–150 mm (0.8-7.9 in).<ref name=":8" /> Pupation can last between 3–11 weeks depending on the temperature and environment.<ref name=":1" /><ref name=":0" /> Pupae are 20 mm (0.8 in) in length and have a shiny, brown appearance.<ref name=":8" /> Adults emerge from the soil chambers and shortly after begin migration.<ref name=":1" /> Adult bogong moths are active at night, and have different seasonal behaviors. During the spring, bogong moths feed and migrate south, where they aestivate during the summer.<ref name=":0" /> Adult bogong moths are not sexually mature yet, and do not actively seek food during this period of dormancy.<ref name=":0" /> In autumn, the moths migrate again and return to their breeding grounds, laying eggs and dying.<ref name=":0" />
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Female dorsal view
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Female ventral view
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Male dorsal view
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Male ventral view
Behaviour
Food resources
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.<ref name=":0" /><ref name=":7" /> 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.<ref name=":0" /> However, the larvae avoid grasses, which overtake pastures during the summer, making summer unfavourable due to lack of larval food sources.<ref name=":1" /> Adult bogong moths feed on the nectar of flowers such as Epacris, Grevillea and Eucalyptus while breeding or migrating, but will not actively feed during aestivation.<ref name=":0" />
Migration
Bogong moths undergo whole scale long-distance migration biannually, in which they can travel up to 965 km (600 miles).<ref name=":9" /> 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.<ref name=":0" /> 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.<ref name=":0" /> The bogong moth utilises 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.<ref name=":1" /> The population within each aestivation site fluctuates throughout the summer due to moth mortality and the departure and arrival of moths either migrating further south for aestivation or north to return to breeding grounds.<ref name=":0" /> However, this differs from changes during migration periods, when the populations rapidly increase with arrival or decrease with departure.
Bogong moths are nocturnal migrants, but the exact mechanism for long-distance navigation is not clear.<ref name=":1" /> It is possible that they are oriented by light, as seen in the influence of light intensity on activity during aestivation.<ref name=":4" /><ref name=":0" /> Additionally, bogong moths may use an internal magnetic compass to aid in navigation, as seen in the similar monarch butterfly.<ref>Template:Cite journal</ref> A study published in 2018 concluded that the Bogong moth uses a combination of the Earth's magnetic field and recognisable landmarks to calibrate their route. In 2025, researchers found that neurons in these insects responded to a starry sky, and suggested Bogong moths use both magnetic fields and stars to orient themselves and navigate.<ref>Template:Cite journal</ref><ref>Template:Cite news</ref>
However, there are also nonmigratory populations; this generally occurs in areas with favourable conditions, where migration to avoid harsh conditions such as seasonal changes in larval food crop abundance is not necessary.<ref name=":1" /> Some populations of bogong moths in areas such as Tasmania and in coastal populations of New South Wales do not migrate, and reach sexual maturity at a faster rate than migratory populations.<ref name=":10" /><ref name=":0" />
Social aggregation
During the spring migration, bogong moths gregariously aggregate with densities reaching 17,000 moths per square metre (10.8 square feet) within caves, crevices, and other areas hidden from the sunlight.<ref name=":5" /> The lack of light and relatively constant temperature and humidity makes these spots favourable during aestivation. The first moths that arrive occupy the deepest and darkest locations, using their fore tarsi to grip onto the rock faces, and aggregations form around these initial areas, with moths arriving later settling for less ideal areas with more sunlight, higher temperatures, and decreased humidity.<ref name=":0" /> To diminish the amount of light that reaches their light-sensitive eyes, later moths push themselves underneath the wings and abdomens of moths that arrived earlier and place their hind legs on top of the moths beneath them.<ref name=":0" /> This physical contact and aggregation allow the moths to retain body moisture. When the aestivating moths are disturbed, the moths within the area of disturbance briefly spread out and leave the aggregation, dropping excrement when unsettled before quickly returning to the aggregation and re-positioning themselves.<ref name=":0" />
While the moths mostly remain dormant during aestivation, there are some periods of activity within the aggregation which are correlated to changes in light intensity.<ref name=":0" /> During dawn and dusk, portions of the population become active, first crawling around and spreading out, and then flying out of their shelter into the open.<ref name=":0" /> While some water drinking has been observed, no evidence of copulation or active foraging has been found during these periods of activity.<ref name=":9">Template:Cite journal</ref><ref name=":0" />
Diapause
Facultative diapause, an optional period of delayed development in response to environmental conditions, accompanies the biannual migration of the bogong moths. While one generation of moths goes through the two migrations each year, multiple generations are possible in favourable conditions and higher temperatures, as growth across all life stages can occur faster.<ref name=":0" /> For example, without the diapause, the bogong moth would normally complete sexual maturation within 50 days.<ref name=":0" /> However, this maturation is delayed due to the lack of larval food sources during the summer season.<ref name=":0" /> During the summer, hot temperatures occur and grasses, which are an unfavourable diet for bogong moth larvae, overtake pastures and make up the majority of the plants occupying the pastures.<ref name=":1" /> Bogong moths avoid this harsh environment by delaying development during the summer so that their eggs do not hatch in a poorly-suited environment; instead, they migrate to cooler, more suitable areas and delay their development during aestivation until the winter season, when they return to the breeding grounds and winter pasture crops begin to grow again.<ref name=":0" /> During aestivation, the bogong moths remain dormant for several months, possibly delaying development due to the lower temperatures.<ref name=":0" /> The food they consume during the migration is also dedicated to building fat reserves for aestivation rather than development, as bogong moths must consume more food during the autumn migration before maturation and mating.<ref name=":0" /> However, in areas with favourable conditions, bogong moths do not have to migrate during the summer.<ref name=":10" />
Ecology
Enemies
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.<ref name=":1" /> Little raven, currawong and Australian pipit congregations form to feast on bogong moths as they travel from aestivation sites during migration.<ref name=":1" /><ref name=":0" /><ref name=":2" /> Aboriginal people also travelled to aestivation sites to feast on the dormant moths, and may have searched for these bird congregations to locate these sites.<ref name=":11">Template:Cite book</ref><ref name=":1" /> Bats also attack the moths during active flight periods during the dusk, and foxes, bush rats, and dusky antechinus have been recorded eating moths.<ref name=":0" /><ref name=":2" /> 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.<ref name=":3" />
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Parasites
Two species of mermithid nematodes parasitise the bogong moth during its aestivation: Amphimermis bogongae and Hexamermis cavicola.<ref name=":0" /><ref>Template:Cite journal</ref> The parasites are transmitted to bogong moths through water; the early instar larval nematodes reside in the debris of the cave floors of common aestivation sites, and crawl up to reach the moths through trickles of water coming down the walls.<ref name=":1" /> Bogong moths are infected upon their arrival within the caves once they drink the water. After a few months, the larval nematodes emerge from the moths, which causes the moth to die, and burrow into the cave floor, where they mature and lay eggs over the winter and wait for the next spring migration of the moths.<ref name=":1" /> The nematodes are unusual in that they parasitise adult bogong moths instead of the more commonly utilised larval host stage.<ref name=":0" /> The nematodes' life cycles demonstrate an adaptation to the migration of the bogong moths, as they are dependent on bogong moths returning to the same aestivation sites.<ref name=":1" />
Biovector of arsenic
Concerns have been raised over the potential role of agriculture in turning the bogong moth into a biovector of arsenic in the Australian Alps.<ref name=":3">Template:Cite journal</ref> Aggregations of bogong moths in aestivation sites has led to the bioaccumulation of the pollutant in both the surrounding local environment and within predators, particularly in the endangered mountain pygmy possum.<ref name=":3" /> However, no conclusive evidence has directly linked agriculture as the source of arsenic in bogong moths.<ref name=":6">Template:Cite journal</ref>
In 2001, a few months after rainfall had washed out debris consisting of dead moths from within the cave, the complete death of local grasses was seen outside of an aestivation site of the bogong moth. Investigation into the causes of the grass mortality showed that the concentration of arsenic in the surrounding areas was much higher than normal, and the source was determined to be the bogong moths. Since the bogong moths do not feed at their aestivation sites, they had absorbed arsenic from lowland feeding sites as larvae and subsequently transported it over long distances into the mountains. Bioaccumulation, the absorption and accumulation of substances by organisms, occurs with arsenic in bogong moths.<ref name=":3" /> While levels within each individual moth are small, the sheer quantity of moths in the area led to a concentration of the pollutant to damaging levels in the environment.<ref name=":6" /> The presence of arsenic has also been shown in the feces of mammals such as the mountain pygmy-possum, demonstrating the bioaccumulation of this pollutant in animals. While no source has been determined, concerns have been raised over the possible role of agriculture in the bioaccumulation of arsenic due to its presence in historically and presently-used insecticides.<ref name=":3" /> This has led to the discontinued use of insecticides in controlling the bogong moth in urban areas, in favour of less intrusive methods.<ref name=":4" />
Decline in numbers
In the spring/summer aestivation seasons of 2017-8 and 2018-9, dramatic drops in numbers of the moths in the Alpine caves have been observed. Millions of the moths have usually lined the walls of these caves over summer, but for the 2017-8 and 2018-9 aestivation seasons there were none in some caves, according to Professor Eric Warrant of Lund University in Sweden. He says that the drop in numbers was probably caused by a lack of rainfall due to winter drought in their breeding areas and climate change, the lack of rain producing insufficient vegetation to feed the caterpillars. Some caves still harboured thousands of moths, which suggested that the moths "came from different breeding grounds, where one location wasn't as badly affected by the drought as the other. I don't think they will disappear completely, but there's certainly a possibility that they could become locally extinct at their breeding grounds.", Warrant said.<ref name=ABCscience>Template:Cite news</ref>
Other biologists and ecologists have pointed to the dramatic effect on animals which feed on the moths, which are an important source of protein for wildlife, including the threatened mountain pygmy possum as well as other insectivorous mammals and birds. "The vulnerability of the Australian Alps to climate change is the worst in the world because we've got these short little mountains so when it gets warmer, there is nowhere for these cold-adapted species to go", according to Euan Ritchie, a wildlife ecologist at Deakin University.<ref name=ABCscience/>
Interactions with humans
Food source
Bogong moths were historically used as a food source by Aboriginal peoples located in South-eastern Australia.<ref name=":11" /> 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.<ref name=":1" /> They would go into the caves and scrape aestivating moths off the walls into nets and dishes using sticks.<ref name=":11" /> 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 "moth meat" cakes that would last and could be taken home.<ref name=":11" /><ref name=":7" /> The moth was said to have a nice nutty flavour that was most similar to walnuts or almonds.<ref name=":7" /> The bogong moth is an icon of Australian wildlife due to this historical role as an important food source and as an inter-tribal gathering point in Southeastern Australia.<ref name=":1" />
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. The Gunaikurnai people were one of the peoples who used to travel to the mountains to obtain the high-fat, energy-rich food, and stories of these travels had been passed down in their oral history. The excavation was done by researchers from Monash University in collaboration with the traditional owners, represented by the Gunaikurnai Land and Waters Corporation (GLaWAC).<ref>Template:Cite web</ref>
Pest of crop plants
Bogong moths have had a role in damaging crop plants since winter pastures serve as breeding grounds and larval food sources.<ref name=":0" /><ref name=":4" /> Outbreaks of caterpillars have been recorded across New South Wales, with damage primarily done to heavy black soil flats.<ref name=":0" /> Medicago species, wheat, cabbages, cauliflowers, silver beet, peas, and potatoes have been recorded as being attacked by bogong moth larvae.<ref name=":0" />
Control
The bogong moth is a minor and irregular pest of crop plants in Australia. This makes it difficult to predict their pattern and control. Typically, control of this species is not cost-effective. However, if there are heavy damaging outbreaks of the bogong moth, insecticide is applied to the crops that are affected by it.<ref name=baileybook>Template:Cite book</ref>
Migration issues
Millions of bogong moths have been blown off course from their spring migration into major cities like Canberra, Melbourne, and Sydney due to strong winds, with notable instances of Bogong Moth invasions including the 2000 Olympics in Sydney.<ref name=":4" /> The large amount of light and noise present can also attract moths towards cities. Parliament House in Canberra, present in the middle of the Bogong Moth flight path during migrations, was notably susceptible to moths.<ref name=":4" /><ref name=":1" /> Light pollution from the building traps them during their flight and encourages the moth to find shelter within crevices, shadows, and sometimes even the insides of the buildings during the light and heat of the day.<ref name=":1" /> Efforts have been made to try and drive the moths out by turning off lights, covering attractive corners and pathways indoors, and using insecticides. However, insecticide use has ceased in urban areas due to concerns over environmental consequences.<ref name=":4" />
Conservation status
In December 2021 the bogong moth was added to the IUCN Red List as an Endangered Species,<ref name=abcredlist>Template:Cite web</ref> based on a February 2021 assessment.<ref name=iucn/>