The housefly
MOST people would probably agree that flies are a pest. They tend to buzz around your head, sit on your food or take over the window sill in the kitchen. There are thousands of fly species on our planet! Yet even common houseflies serve a purpose – they’re food for many animals, including birds, frogs and snakes.
The housefly (Musca domestica) is probably one of the most common insects. These flies are found virtually everywhere there are people; only Antarctica and perhaps a few remote islands in the polar regions don’t have them.
Flies are used to living around humans and animals so they’ve adapted to survive in habitats where there are people. Scientists believe the housefly evolved in the Cenozoic (most recent) geological era, which began 65 million years ago, possibly in the Middle East, from where it spread all over the world. Throughout history, whenever people have moved to new places – whether by sea, air or even with horse-drawn carts – flies have always accompanied us. Flies aren’t only irritating, they also spread disease. The housefly thrives on things we regard as dirty: garbage, animal waste, sewage and other disgusting things. You’ll also find them on compost heaps, where there’s dead plant material and rotting fruits and vegetables. As a result, flies tend to spread diseases from place to place as they move around.
A housefly may land on a pile of dung then fly to where you’re enjoying a braai and step all over your delicious lamb chop or potato salad. More than 100 human and animal diseases are spread by houseflies, including
SPREADING DISEASE
cholera, salmonella and typhus.
People use insecticides to try to get rid of flies but with thousands of different species in existence we’ll never be able to destroy or eliminate them completely.
THE LIFE CYCLE OF A HOUSEFLY
There are four phases in its life cycle: egg, larva (called maggot), pupa and adult. A female housefly can produce more than 500 eggs during her short lifespan. She lays 100 to 150 eggs at a time – often on or near rotting meat such as a dead animal.
The larvae or maggots start hatching within a day and eat the rotting meat or other rotting material nearby, such as garbage. As soon as they’re old enough (two to five days), the maggots crawl to a cool, dry place and change into reddish brown pupae. A few days later they emerge from their shells as fully grown flies.
Houseflies have only two wings but these allow them to fly up, down, sideways and even in reverse! Their hairy, sticky feet can walk on virtually any surface – even upside down on the ceiling.
Flies can’t fly fast – they have an average speed of about 7 km/h. In densely populated urban areas – where there’s often a lot of waste for flies to survive on – they don’t need to fly far, so their territory will be about a square kilometre. But in rural areas houseflies can fly up to 7 km in search of food.
Flies don’t have teeth. Instead they suck up their food with their mouth, which works like a sponge. This means they can ingest only liquids, so they dissolve solid food by spitting or vomiting on it. Their vomit contains digestive substances that dissolve solid food material. A housefly’s tongue resembles a drinking straw, which allows it to suck up its food. Flies can eat any wet or rotting material but they prefer animal faeces as it’s strong smelling and easy for them to find.
THE POSITIVES
This might seem gross yet flies have an important function in Earth’s ecosystem. They don’t work quite as hard as bees at it but flies play a significant role in pollinating flowers, either because they eat nectar or pollen, or because they’re attracted to flowers that mimic the smell of rotting meat or dung. They also help to break down organic material such as rotting food faster.
The larvae of certain flies eat only harmful bacteria and secrete an enzyme that speeds up the healing of wounds. This is why they can be used to disinfect wounds. There’s evidence that the Mayans of Central America and the Aboriginal people of Australia used to apply maggots to wounds to clean them. One of the first written reports about larval therapy comes from the 16th century when French doctor Ambroise Paré used fly maggots to help soldiers heal from their battle wounds more quickly. S