The intricate world of flies
The flies that bug us so much over summer play a crucial role in the Australian ecosystem and are some of the most diverse, tenacious, fascinating and attractive insects around.
Though you may have watched male lesser house flies (Fannia canicularis) in their constant dance around your lounge room light and loaned your back to bush flies (Musca vetustissima) on a hot summer's day, you may not have met a fly with its eyes on stalks, or one that spends its entire life upside down. There is much more to flies than meets the eye.
Flies are an essential part of the food chain. Their lives are inexorably tied up with the native flora and fauna of their habitat and they play an important role pollinating plants and recycling all things dead and decaying. They have conquered habitats from Arctic forests to Australian deserts in a way paralleled only by the beetles amongst the animal world.
"They inhabit almost all areas of the Earth that are inhabitable," says Dan Bickel of the Australian Museum's entomology department.
Flies are members of the order Diptera, which includes mosquitoes, crane flies, sand flies, midges and gnats (members of the sub order Nematocera). There are plenty of flies out there, as a stroll in the Australian bush will testify, but there are also many different species of flies - an estimated 30,000 in Australia in 104 families, with only around 8000 so far scientifically described and named.
In spring and particularly in summer many flies celebrate the sunny conditions by swarming over the countryside. The reason for this is the increase in temperature. Flies can't regulate their own temperature, so when it's hotter, they are able to fly faster, grow faster and breed faster. In summer their life cycle cranks up and flies make the most of the opportunity to lap, pierce or suck a range of foodstuffs from flowers to faeces. Spring and summer are also when food supplies increase: there are more flowers for pollinating nectar-feeders and more caterpillars and beetle larvae for parasitic insect-feeding flies.
The life of flies
Most flies possess two pairs of wings with the second pair reduced to small balancing struts called halteres. Some flies have lost their characteristic ability entirely and the adults have reduced wings or no wings at all. West Australian pitcher plant maggots live in the pool of liquid that is the digestive system of the insectivorous Albany pitcher plants. The maggots make a tasty living feeding off the drowned ants trapped in the liquid and at some time crawl out of the plants, eventually emerging as long-legged, wingless adults which frequent entirely different plants.
Like all insects, a fly's life cycle begins as an egg, often deposited in an environment that maximises its potential to find food. Some insect-eating flies from the family Tachinidae lay their eggs in the body of the host creature they dwell in, while others actually flick their eggs into bee or wasp nests to provide their developing larvae with a whole room full of tasty morsels. Bush flies lay their eggs in dung, while blow flies lay their eggs in cadavers, wounds in flesh and dung-caked wool, causing sheep to become 'fly-blown' or fly-struck around their hindquarters.
The kangaroo bot fly finds a warm repository in the form of the elementary canal of its host the kangaroo, where it lives until it emerges as an adult.
The larvae of some flies are of course maggots. As unattractive as they may seem they play a vital role in assisting the decomposition of dung and dead and decaying matter, whether plant or animal. The voracious appetite of maggots for all things decaying has and occasionally still is used to clean the flesh on wounds.
Yummy, maggots. Image: National Institutes of Health, part of the United States Department of Health and Human Services [more pics]
Once a maggot is fully-grown it will find a place to rest, burying itself into the ground, a piece of fruit, or the body of another creature, and pupate. It forms a hard shell around its body and undergoes a miraculous transformation, emerging unrecognisably different in bodily structure. Often connecting the two stages of life cycle is a difficult task as the adult may have entirely different feeding habits and prefer a different habitat than the larval stage.
A fly's adult life is brief but spectacular. In summer, a house fly's (Musca domestica) life expectancy can be as little as seven to 10 days, while in colder conditions they may live for as long as a month. During that time a female house fly may lay as many as 500 eggs in batches of 75 to 150 at a time.
When: The fly cycle really takes off from spring to mid-summer, but flies can be found year round.
Upside down flies
Entomologist David McAlpine, now retired from the Australian Museum, spent much of his life studying Diptera. He was the first scientist to examine a set of flies with an unusual behaviour - the upside down fly.
"As soon as I observed the living fly I realised it has this strange behaviour of always clinging on to a vertical surface with the head hanging down," says McAlpine.
Walking forwards means walking down to an upside down fly. Turn their home around and they will re-orient themselves in their preferred position. Found throughout Australia and also in Zimbabwe, Madagascar, Malaysia and New Guinea, the upside down flies were once believed to be extremely rare. But find their favourite habitat, as McAlpine did, and they are actually quite abundant. In Western Australia upside down flies frequent tall grass trees known as black boys (Xanthorrhoeaceae), while in eastern Australian rainforest they are associated with native cunjevoi (Alocasia brisbanensis or A.macrorrhiza ).
Walk in the Australian bush for any time and you are likely to notice the cubic droppings of one of our iconic species - wombats. These dropping are the favoured habitat of wombat flies, a little known species classified in a taxonomic section between family and genus called a tribe, the Borboroidini.
McAlpine studied and described most of the 24 known species of this tiny fly by the novel method of spreading wombat dung, donated by a local zoo, in wombat-inhabited areas. One of his first deposits of 'bait' yielded three previously unknown species, which McAlpine was never able to find outside the original site.
Stalk-eyed flies face off
Stalk-eyed flies are flies whose male members compete for territory and female attention with their striking appearance. While females possess a more ordinary facial structure it seems for the males the longer their eye stalks are the more successfully they are likely to be at reproducing. Males display in front of each other by quite literally staring down the competition.
Common or garden flies
Apart from the coppery-green or blue blow flies and the ordinary house fly (which even at close glance may be striking in appearance, with red eyes and greenish colouring), flies you might find floating around the garden include hover flies, fruit flies and insectivorous robber flies.
Stripy, yellow hover flies are flower-lovers who have evolved the very simple defence mechanism of mimicking bees and wasps in their stripy appearance and occasionally, narrow waists. They fly in a characteristic pattern, hovering and darting suddenly to the side.
Mediterranean fruit fly
Fruit flies are considered a pest species, particularly the Queensland fruit fly and Mediterranean fruit fly. Potential losses to the Australian fruit economy run into the hundreds of millions and strict measures are taken to restrict these flies. Of the over 80 species however, many of the small to medium sized flies are useful members of the food cycle and they particularly inhabit warm humid conditions, recycling fruit in rainforest areas.
Robber flies (family Asilidae) can grow quite large (up to 30 millimetres) and possess powerful, grasping leg claws and venom to help them immobilise their prey, which can include bees and even spiders.
Further info and credits
The intricate world of flies was written by Heather Catchpole. Thanks to David McAlpine, Max Moulds and Dan Bickel of the Australian Museum, Sam Cotton from UC Berkeley and CSIRO Entomology.
Published 08 February 2007