Stepping out into your garden in recent weeks, you might have noticed thousands of tiny, white butterflies hovering around the plants and trees — and if so, you're one of many Aussies who've witnessed an extraordinary but worrying sight.
Scores of residents have expressed their amazement after witnessing "hundreds" and sometimes "thousands" of white-winged insects taking over the sky and gardens across Victoria, and some in Sydney too, leaving many wondering what has caused the sudden mass emergence.
Taking to social media on Saturday, one woman from Geelong said there was "a plague of them" near her home. "The sky, trees and flowers are covered in them," she said admitting she's "never seen anything like it before". Another agreed," they're everywhere today" sharing an incredible video showing hundreds of white-winged insects flapping around the garden.
Invasive species takes over Aussie suburbs
What we're seeing is an influx of Pieris rapae, commonly known as "cabbage moths" — an invasive species of butterfly originally from Europe, considered a pest in Australia. This is because they will snack on any plant from the brassica family, which includes lettuce, cabbage, broccoli, cauliflower, kale and brussel sprouts — and ruin crops.
As incredible as they may look, the "beautiful" butterfly — found across most of eastern Australia — can be problematic, Simon Hinkley from Museums Victoria told Yahoo News Australia. While it happens every year, he agreed he's seen more than usual this year and said the astonishing number we're currently seeing is alarming.
Why are there more white butterflies than usual?
The reason for the large numbers is likely due to the climate, Dr Darrell J Kemp from Macquarie University explained to Yahoo News. "This is because their larval hostplants grow best at those times, in more 'normal' years," the Associate Professor of Biology said.
But this year, "we had much more rain in December and early January, which has created greatly favourable breeding conditions for them," he noted. "A spurt of hostplant growth across large areas of south-eastern Australia", meaning they've been able to "extend themselves into summer".
A mild winter last year meant more pupae — the stage in which a caterpillar metamorphoses inside a cocoon into an adult butterfly — survived but stayed dormant before moving into a wetter-than-usual spring, meaning they didn't emerge. This combined with hotter temperatures moving into summer created the perfect environment for butterflies and other insects to thrive.
What's more, the butterflies are "incredibly fast growers" with each female laying roughly 800 eggs on the underside of leaves at once which could mean we're seeing "multiple generations a year".
'Cabbage moths' wreak havoc on Aussie gardens
Hinkley, Collection Manager of Terrestrial Invertebrate at the museum, said the butterflies are very much "established" in Australia and are "impossible" to get rid of — so those with crops or vegetables growing in their garden should beware.
"They're not problematic in the sense that they don't sting, they don't bite, they don't damage our house," HIckley explained. "But if you are a keen vegetable grower, [they have] potential to cause damage to your backyard crops. So that's where people may want to take some precautionary measures."
Concerned Aussies can spray their plants to rid them of the eggs or caterpillars, but this "often leads to killing beneficial insects". Instead, Hinkley suggests having a "variety of plants and flowering plants that can attract predatory insects, that will then move on to things like cabbage white larvae".
"But if you've got an absolute swarm of caterpillars on your plants, you can just literally pick them off and throw them to your chooks, if you've got chooks, or do what you like with them, " he said. "But as we move into cooler weather, the numbers will drop off. So they won't maintain this huge population peak during the winter."
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