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Dr James Wallman, from the School of Biological Sciences at the University of Wollongong points out that while many people equate insects with creepy crawlies and are quick to squash or spray them, the descriptors of harmful, dirty, and dangerous applied to insects is unwarranted as they play a vital role in how the world functions.
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| Bees, for instance, pollinate many of the plants that supply us with food. Many people may not realise that flies are also important as pollinators.
The positive aspects of flies are rarely highlighted and while people may reel at the thought of maggots, they have been used to save people’s limbs in what is known as 'maggot debridement therapy'.
Photo: J F Wallman
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Here, maggots are deliberately placed into the wounds to help heal them as some wounds do not respond to drugs. The maggots only eat the dead tissue and their movement helps promote blood flow. Amazingly, their saliva also contains special chemicals that help kill harmful bacteria.
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| In other contexts, flies and maggots help break down the tissues of dead creatures. They do this very rapidly, the baby flies (the maggots) having voracious appetites which explains why we hardly ever see the dead bodies of birds or other little animals on the ground. The nutrients from this process are returned to the ecosystem where they can be used by other organisms, such as plants.
Maggots at work.
Photo: J F Wallman
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Flies are part of a broad group of insects with some several hundred thousand different species in the world. Mosquitoes are in fact flies and there are many more harmless ones than their reputation belies. Some fly species also help break down plant material so the important decomposition and recycling work they do is not isolated to animals.
The small, black bush flies, abundant in Australia in summer, breed in animal droppings and are instrumental in breaking these droppings down. They are annoying, however, in their vast numbers so scientists introduced dung beetles to alleviate the numbers of bush flies - a mostly successful introduction. Prior to European settlement the bush flies only had droppings from animals such as kangaroos to breed in. The introduction and expansion of cattle industries increased the provision droppings many times over, so that bush fly numbers were able to increase dramatically.
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| Lucilia cuprina - the sheep blowfly. Photo: R. Major
The sheep blow fly, an introduced species from overseas, is a problem in the sheep industry as their maggots will feed on live flesh as well as dead tissue, which causes distress to the sheep, loss of condition and fleece quality and economic cost to the farmer.
Interestingly the good side of these flies is that they can be used in forensic investigations as they may be among the first to the scene of the crime.
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Some flies seem quite strange. For example, some behave more like fleas or lice, having flattened bodies and infesting animals such as kangaroos, gripping onto the kangaroo’s fur. Other such flies infest some of our birdlife by clinging to the feathers. Both sorts of flies feed by sucking the blood of their hosts.
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Flies are mostly not harmful in themselves, although we can become sick from diseases carried by mosquitoes. |
| Indeed, despite their feeding habits, we are unlikely to fall ill from anything that flies deposit on our food, despite our constant attempts to protect our food from them.
Even accidentally eating maggots is unlikely to harm us as they mostly cannot survive in our stomachs (think of it as a bonus addition of protein!).
While the insecticide industry panders to our paranoia about flies, they really do very little harm.
Calliphora - the common house blowfly. Photo: R. Major
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A cheaper control for flies in the house would be to shut all blinds and open the front door which will make them leave as flies are attracted to light. Other images which feed our paranoia of flies are those of children, usually from impoverished places, with flies all around their eyes. The flies are trying to get water and protein from the tears around the eyes, a process that is perfectly natural as they need the protein to mature their eggs. They are not the cause of the child's impoverished condition and certainly are not laying eggs or harming the child.
The idea that healthy humans can become fly blown is more likely to be imagined than real. On rare occasions (e.g. a car accident where the victim is not found for some days), there have been reports of open wounds with maggots in them. These injuries may have attracted flies like those used in maggot therapy and the maggots will in fact be cleansing the wound. Reports from battlefields over the decades are well known for the superior healing of wounds sustained by soldiers if their injuries had become maggot ridden.
It seems our own battlefield with flies is more based on fiction than fact and flies in the face of scientific knowledge.
Text: V.B. Jan 2010
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