Christmas beetle numbers on the decline as imposter numbers grow


Just like Santa Claus, when it comes to Christmas beetles the real thing is bigger, rarer and shinier than the fakes that abound in Sydney’s centre at this time of year.
Experts from the Australian Museum say the Christmas beetles reported in Sydney’s more populous areas are likely two impostors, an Argentine lawn beetle and the native chafer.
”Clearly some people are confusing them,” said Chris Reid, a research scientist with the Australian Museum Research Institute.
There are about seven species of Christmas beetles found in the bushier areas of Sydney, including suburbs near the Royal National Park and Ku-ring-gai.
The impostors are dull brown and about 1.5 centimetres long. In contrast, the real thing is shiny, often an iridescent green or metallic brown in keeping with the season, and twice as large.
To tell apart the species, entomologists look at the insects’ bums, which are easy to see, Dr Reid said. The king beetle, about 3.5 centimetres long, has a dull-green rear, he said. Another large species that reached pest proportions in the 1920s had an orange tufted rear.
The washerwoman species of Christmas beetle has a shiny posterior and is about 2.5 centimetres.
”In the 1920s, there are records of Christmas beetles being so common around the harbour that the branches of eucalypts were hanging down into the water,” he said.
While Christmas beetles are common in rural areas, the washerwoman (a type of scarab) is considered a pest in areas such as Armidale, Dr Reid has not seen one in the inner city in the past 15 years. But he has seen many impostors, which people may mistake for Christmas beetles. The impostors thrive in garden lawns. While they are growing in numbers, Christmas beetle numbers are falling because of the decline in habitat.
The adults mainly feed on eucalyptus leaves and prefer open woodland to forest, thriving in pastures where trees have been left in place. On farmland they can form dense masses on remaining eucalypts, chomping through leaves, sometimes killing their hosts, while their larvae feed on roots, usually grasses.
Correction: The caption on the original version of this story said the Argentine lawn beetle was on the left and the native chafer was on the right, instead of the other way around.

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