Question: Why are there so many hover flies around?
It seems to happen this time every year. Canberra emerges from the cold wet winter and becomes a thriving mecca for plants, pollen, and hover flies.
Stepping into your garden, you've probably noticed the starfleet-like swarm of these bee-mimicking flies hovering over your plants, giving the fly their common name.
Hover flies are a group of true flies that include more than 6000 described species spread throughout the world. Should you be worried about these flies, or what they are doing to your garden? Simply put, no.
The number of hover flies seems to explode in early spring due to the increase in aphids, the small sap-sucking insects that threaten the health of your garden. A wet winter can promote weed growth, creating the perfect storm for aphids.
Fortunately, our gardens already have a natural biosecurity force defending our plants: hover fly larvae. Similar to butterflies, hover flies undergo a series of developmental stages during metamorphosis, including the egg, larvae, pupa and adult. Hover fly larvae are green caterpillar-like maggots that naturally predate aphids and eat them before they can do damage to your garden.
As the number of weeds increases over winter, so does the aphid food source and the hover fly population increases.
Hover flies are also fantastic pollinators. Adult flies feed on energy-rich nectar from flowering plants, and while eating, their hairs get covered in pollen which is transferred from plant to plant, leading to pollination.
It's this effective pollinating behaviour that has led to some avocado farmers in Western Australia planting grasses and flowering plants on their farms to attract hover flies to pollinate their orchards. Pollination by insects is estimated to be worth more than $6billion per year in Australia. Without flies, there would also be no chocolate as they are the only known pollinator of the cocoa plant.
So the next time you get buzzed by a fly, perhaps put down the fly spray and pick up a cup of tea and enjoy the wonderful biodiversity pollinating your garden.
■ Watch a hover fly larvae take down an aphid: https://www.youtube.com/watch?v=N7CQmlF_jJA
Response by: Dr Bryan Lessard – aka. Bry the Fly Guy – from CSIRO's Australian National Insect Collection.
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