Sydneysiders have faced an initial onslaught of flies, meddling with social gatherings and weekend plans.
While their presence is not unusual, it is more visible this year and earlier than usual, according to scientists.
With an unusual start to spring, With El Niño and climate change promising rising temperatures, winged insects have found ideal conditions in the port city.
Thousands of species, millions of flies
University of Sydney evolutionary ecologist Thomas White said it was difficult to determine the exact number of flies, but called this week’s figure “significant”.
“I’ve seen a real explosion in the numbers,” Dr. White said.
He personally saw them invade the street and “annoy” people at the beach.
He attributes this to the fact that flies are attracted to large gatherings in warm weather.
There are 30,000 different species of flies, according to the CSIRO.
Scientists usually set small traps or visually inspect areas where flies are common to get an idea of their numbers when conducting research, Dr. White said.
However, due to their short life cycle and ability to lay hundreds of eggs per week, anecdotal evidence is the best way to assess sudden peaks and valleys.
The sun brings out the swarms
This year, the start of the season was exceptionally warm.
A wave of hot air hit Australia last weekend and September broke an all-time world temperature record by an “extraordinary amount”.
“It’s quite dry, we’re in El Niño and there’s been this string of 30 or 40 degree temperatures that are out of the ordinary for this time of spring,” Dr White said.
From eggs to larvae, pupae to adulthood, temperature plays an important role in a fly’s life cycle.
Higher temperatures can speed up the time it takes for a fly to mature to just a week or two, instead of the usual three or four.
The weather also meant the crowds came out earlier than usual.
“There may have been a bit of a delay, but really they just like warm, humid weather,” Dr. White said.
“And because it’s so hot and humid, they’re here in greater numbers than we’ve seen in the last couple of years… where it was a little cooler and a little wetter.”
Dan Bickel, an entomologist at the Australian Museum, said people tended to forget about the flies until a big heatwave.
“They come in droves and it seems like overnight they are there, but they can leave just as quickly,” Dr. Bickel said.
“The air masses move and carry with them all kinds of flying insects.
“A lot of the ones that came in the other day were probably destroyed by this cold front that just happened.”
Flies love human oils
They may all look pretty much the same as your arms flail around trying to fend them off, but there are many, many different types of flies.
“They have a variety of different ecological habits and lifestyles,” Dr. Bickel said.
“Sometimes people encounter them and find them unpleasant, other times they more or less do their own thing.”
One of the most commonly reported culprits is the humble bush fly, which Dr White says is harmless and does not transmit disease.
“They’re really just a nuisance and they’ve given rise to the ‘Australian salute’, where you have to keep them off your shoulders and off your face,” he said.
Dr Bickel added that bush flies benefit from the moisture of sweat and tears and get their nutrients from the oils in human skin.
“It’s a hot day, there’s sweat, they may sit on you or get close to your eyes and suck some of the salty secretions out of your body.”
Other species encountered include mosquitoes, March flies (also known as horseflies), and houseflies which like to feast on food scraps and animal droppings.
As for why they never seem to give up, Dr. Bickel explained that flies view humans as a walking source of energy.
“They know there’s still more to do, and so they’re going to come back persistently unless they find a better source nearby.”
Radical climate change brings new normal
Dr Bickel said spikes in fly numbers provided a good opportunity for people to connect with nature and changing conditions.
“Be aware of your surroundings, such as dramatic climate changes.
“It’s always good to notice things, see what’s happening…flies are just part of the mix.”
According to Dr. White, it is difficult to predict the role that climate change will play on flies in the years to come.
“The numbers of some species will increase significantly, while others will have a more difficult time.”
The areas where the flies are found can also change over time, with some species migrating south to warmer climates, he said.
How can we keep them away?
Experts say it’s time humans learned to live with them and keep their hands off insecticides.
“They are pollinators, nutrient recyclers, they are great and essential,” he said.
“So, really, people can just brush them off, move on and not worry about it too much – as best you can.”