Ghosts of Christmases past
Do you remember when hordes of large, brightly coloured scarab beetles used to descend on Aussie summertime gatherings like mobile festive decorations?
Christmas beetles were said to be so numerous 100 years ago in the Sydney region that they could be found f loating in the harbour in huge numbers at this time of year.
These iridescent insects were known to swarm in such quantities that the boughs of eucalypt trees would regularly bend under their weight.
Once common in summertime – particularly at night around streetlights or as visitors at barbecues in eastern Australia – these large and often colourful scarab beetles comprise 36 different species, nearly all of which are endemic to Australia. They’re all in the genus Anoplognathus, with the common names of some species including king, queen, and campf ire beetle, washerwoman and furry tailed prince.
But you may have noticed that they are less common than they used to be, with these metallic pink, brown, green and gold insects likely to be experiencing similar declines in numbers that are blighting other insects worldwide, particularly in urban areas (see Wild Australia, AG 150).
According to Australian Museum experts, the evidence for declines in New South Wales is anecdotal but compelling. A February 2019 poll of Queenslanders by online newspaper Brisbane Times found that more than half of those surveyed either hadn’t seen a Christmas beetle in six months or couldn’t remember the last time they’d spotted one.
Perhaps unsurprisingly, increasing human population numbers and habitat loss are implicated as the most likely causes for declines.
Sydney’s human population grew from just over 4 million in 2011 to more than 5 million in 2018. Meanwhile, Cumberland Plain woodland in Western Sydney – once rich with eucalypts that adult Christmas beetles feed on – now covers less than 10 per cent of its original area. Habitat loss is also implicated around Brisbane, with land clearing rampant in south-eastern Queensland, and many of the native grasslands – required by juvenile stages of the insects for food – now swallowed by suburbia.
Precise f igures on declines are hard to come by because there has been little long-term monitoring of Christmas beetle numbers, meaning natural f luctuations in populations cannot entirely be ruled out.
Climate change is likely to be another factor in declines, experts say. Christmas beetle larvae usually pupate into adults from about November or December and the adult stage only lives for a few weeks, during which time they must mate and lay eggs. Unusually dry spring weather can delay development of pupae into adults until the following year, which can mean fewer beetles around in a given year.
Insect populations have been declining worldwide, with some studies suggesting the problem is signif icant.
In 2018 Australian entomologists collated 73 longterm studies of insect numbers from across the planet and warned that the extinction of 40 per cent of the world’s insect species was possible in coming decades.
They advised of potentially catastrophic impacts on ecosystems, which are often underpinned by the insects that reside in them, and on agriculture, which is dependent on the pollination services they provide.
While some think of Christmas beetles – named for their yuletide arrival and festive bauble-like appearance – as pests, many will cast their minds nostalgically back to their youth and lament this pretty little creature’s decline. JOHN PICKRELL is a former AUSTRALIAN GEOGRAPHIC editor. Follow him on Twitter: @john_pickrell