What has six legs and loves the electrolytes oozing from your eyes? This fly.
Insect populations are booming across New South Wales, with flies swarming beachgoers, catching rides on pedestrians’ backs and trying to get a drink of the tasty nectar seeping from people’s mouths.
But are there more flies than usual – or has Sydney just forgotten what all the buzz is about?
Why are there so many flies around right now?
“This call happens every year,” Tanya Latty, an entomologist and researcher in insect behaviour at the University of Sydney, tells Guardian Australia. “It’s spring in Sydney, that’s kind of what’s happening. We get used to there not being a lot of flies over winter, and when they show up in the spring, every year people ask if there are more than usual.”
The flies plaguing Sydneysiders’ faces are largely one notable and endemic species: the Australian bush fly. The insects love the moisture and electrolytes in the eyes, ears and mouths of mammals, including humans.
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“They like to drink your sweat and your tears, it’s got traces of various yummy things that they like,” Latty says, adding that while the insects don’t bite, they regularly “make a nuisance of themselves”.
Dan Bickel, a research scientist with the Australian Museum’s entomology collection, says the wind linked to last week’s record-breaking heat in NSW could be to blame for a sudden crush of flies that seemingly appeared “overnight”.
“Bush flies often come in with the winds that come off the interior, they can kind of drive in almost overnight,” he says.
Bickel says bush flies will breed in dung in warmer areas with pastures or farmland and then migrate on the winds, akin to the scores of bogong moths that used to blanket Sydney. The critters establish themselves in populated areas for their short lifespan of a couple weeks. The flies will mate and lay eggs but can die back if there isn’t much material, ie dung, around.
What are the best conditions for fly hatching season?
Bryan Lessard, an entomologist based in Canberra known as Bry the Fly Guy, says a period of wet weather followed by warm temperatures makes a perfect hatching season for a whole host of insects that lie dormant in the winter.
“It shouldn’t be a surprise, because in spring it’s a lot warmer and there’s a lot more rain, and it’s the perfect recipe to really cause a boom in the insect population,” Lessard says.
He says Sydney plays host to a few generations of flies in spring and summer, saying it wasn’t just one big burst but more of a cyclical hatching and mating cycle through the warmer seasons.
“All insects undergo metamorphosis and they rely on the right weather conditions for their life cycles,” he adds. “They’re all going to start emerging now.”
Aside from flies, warm and wet conditions also favour cockroaches, moths and a host of other fly species. Australia has an estimated 30,000 different species of fly, many of which are pollinators for crops and native plants. Another species, the Australian blowfly, loves breeding in food organics garden organics bins, which have the protein-rich environment they love.
Why are flies important to the environment?
Latty says insects in general are cold blooded and their metabolism is tied to the weather around them. Many slow down or effectively disappear in the colder months but when the weather warms they do too.
“Spring and summer is just this glorious time,” Latty says.
Many of those insects are seen as lovely and garden-friendly: for example, butterflies, ladybirds and hoverflies that eat aphids on plants.
Lessard also notes that while there are 10 species of cockroaches in Australia that are seen as pests, there are 500 native species “that will never come into our kitchens or houses because they’re too busy eating leaf litter in the rainforests”.
All three experts noted that the insects, flies included, are deeply important for a robust ecosystem.
“If people wish they lived in a world without flies, we’d all be stuffed because they’re our essential workers in nature,” Lessard says.
Letty stresses that flies are important worldwide, pointing to a particular product sure to be in Halloween candy buckets this week: chocolate.
“If you like chocolate, you have to like flies because that’s pollinated by a fly species,” she says.
“Flies are good,” she adds.
