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Bushfly – a true Australian

The bushfly, Musca vetustissima, is an Australian icon.  You know the one.  It’s that little fly that sticks to you en masse – they make you choke when you breathe them in and they get in your eyes, ears and nose!  The famous “Aussie Salute” is a sure sign they might be around.

Photo credit: Jean Horton https://www.flickr.com/photos/jean_hort/8169257975/in/photostream/

The bushfly breeds by laying eggs in animal dung.  The eggs hatch into larvae which feed in the dung.  After moulting twice, the larvae stop feeding and enter the soil where they turn into pupae.  The young fly develops inside the puparium and emerges from the soil to complete the lifecycle as an adult fly.  

The Newcastle Sun. 17 Nov 1952, p2. In the early days

The Newcastle Sun. 17 Nov 1952 P2

Once upon a time in Australia, before cattle and sheep were brought here, the humble bushfly laid its eggs on marsupial dung.  Bushfly numbers were naturally regulated by the action of competitor species such as native dung beetles and predatory mites and beetles.  When cattle were brought to Australia, the bushfly thrived.  They were able to capitalise on the sudden introduction of large dung piles into their environment.  The larvae from the eggs they laid into this new resource were free to develop without pressure from the native competitors and predators because those species, adapted as they were to manage pelletised dung, did not seem to be able to switch to the new resource in the same way. 
Perhaps if the bushfly had stayed in the bush, Australians would have been more likely to just put up with them.  But they had a nasty tendency to turn up in plague proportions in the city too (“Plague of Bush Flies,” 1952) so something had to be done.
In the 1960s, scientists with the CSIRO began to study the biology of the bushfly.  They noted that the flies could be found in all parts of  Australia in all types of open country from the central deserts, across grazing lands to the sea shore and all altitudes to the tops of mountains (RD Hughes, Greenham, Tyndale‐Biscoe, & Walker, 1972).  The flies were observed to disappear from the southern third of Australia in winter but apart from that, they appeared to tolerate a wide variety of conditions.

The CSIRO steps in

Other studies found that the quality of the cattle dung affected bushfly larval survival and the reproductive potential of the ensuing adults (Greenham, 1972).  Spring pastures tended to produce rich cattle dung that favoured bushfly growth, whereas when the pastures matured, more dry matter was incorporated into the cattle diet making the dung less suitable and reducing bushfly reproduction.

Blown in

Another interesting feature discovered about the bushfly was its ability to migrate en masse.  The bushfly was understood to disappear from southern parts of Australia during winter, and yet it would reappear, often in large numbers rather suddenly, in spring.  Some fly species “overwinter” in cold regions because one part of the lifecycle is well adapted to withstand the cold.  For some species the larval or pupal stage of the lifecycle may enter a period in which their development is temporarily halted during the cold.  Then when the weather warms up again, they are stimulated to continue their development and emerge as flies in spring.  However, studies on bushfly population dynamics revealed that this was not a strategy used by this species.  Rather, they were found to use warm northerly winds in spring to carry them in numbers from the warm northern regions into southern areas which were becoming suitable for their survival due to the warming weather (R. Hughes & Nicholas, 1974). 

Introducing dung beetles

To help combat the plagues of bushfly, the CSIRO investigated the use of introduced competitor species, particularly dung beetles to remove the main resource for bushfly larvae, namely the cattle dung.  Many dung beetle species have been introduced over the years and a good number of these have successfully established in various areas of Australia ((“Introduced species in Australia,” 2020) and for example see (Cousins, 2019)). In addition to making the dung unavailable for bushflies, they also improve the fertility of the soil through the incorporation of dung into the soil and improve the permeability of pasture soils to rainfall (Weston & Evans, 2020).

Last summer, large swathes of northern Victoria and New South Wales and parts of South Australia were engulfed in ferocious bushfires and prior to that the country was in drought. 

Researchers are busy trying to determine how these conditions might have affected dung beetle populations (Jess, 2020) and what the effect may be on bushfly numbers this coming season (Goodwin, 2020). 

Copris hispanus  Photo credit: Jan Botha https://www.dungbeetlessouthwest.org.au/copris-hispanus

With the rainfall outlook for south-eastern Australia looking fairly positive for spring this year, it could well be a favourable season for the bushfly, but time will tell.  If they do turn up in large numbers this year, setting EnviroSafe Fly Traps can help by reducing the population in your immediate area.

Further reading

Cousins, D. (2019, 29 May 2019). Control of bush flies by dung beetles. Retrieved from https://www.agric.wa.gov.au/land-use/control-bush-flies-dung-beetles

Goodwin, S. (2020). Dung beetles prove resilient in bushfires. Retrieved from https://www.theland.com.au/story/6673599/dung-beetles-prove-resilient-in-bushfires

Greenham, P. (1972). The effects of the variability of cattle dung on the multiplication of the bushfly (Musca vetustissima Walk). The Journal of Animal Ecology, 153-165.

Hughes, R., Greenham, P., Tyndale‐Biscoe, M., & Walker, J. (1972). A synopsis of observations on the biology of the Australian bushfly (Musca vetustissima Walker). Australian Journal of Entomology, 11(4), 311-331.

Hughes, R., & Nicholas, W. (1974). The spring migration of the bushfly (“Musca vetustissima” Walk.): evidence of displacement provided by natural population markers including parasitism. The Journal of Animal Ecology, 43(2), 411. doi:10.2307/3373

Introduced species in Australia. (2020). Retrieved from http://www.dungbeetles.com.au/species

Jess, A. (2020). Dung beetle expert predicts severe bush fly problem across NSW and Victoria this summer. ABC Goulburn Murray, 2020. Retrieved from https://www.abc.net.au/news/2020-06-21/predictions-of-more-bush-flies-this-summer/12376776

Plague of Bush Flies. (1952). Retrieved from http://nla.gov.au/nla.news-article160400537.  Retrieved 31 Jul 2020 http://nla.gov.au/nla.news-article160400537

Weston, P., & Evans, T. (2020). How the humble dung beetle engineers better ecosystems in Australia. Retrieved from https://theconversation.com/how-the-humble-dung-beetle-engineers-better-ecosystems-in-australia-101975

https://www.dungbeetlessouthwest.org.au/

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