It’s an emotional time to be an entomologist, as ecological diversity that once existed slips away

The humming of Christmas beetles was once a sign of the season. Where have they gone?

How many Christmas beetles have you seen this year?

The insects – a genus containing some 35 separate species – traditionally appear in summer. Many settlers saw the scarabs, shimmering in festive red and green, as embodying the European holiday tradition.

“Some forgotten chord is strumming,’ explained the folk poet Clement R E Grainger back in 1932, ‘when beetles start their humming/ for they speak of joy and gladness/perfect love and deepest woe.”

Today that humming’s become much more difficult to hear.

Those of us who remember the beetles from our childhood can’t help but notice how rarely they appear now.

Entomologist Chris Reid, a research scientist at the Australian Museum, says beetle populations have almost certainly declined.

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“From my own experience, I have not seen Christmas beetles in numbers in the southern suburbs, where I live on the edge of Royal National [park], since about eight or nine years ago.”

But we lack hard data on their situation, in a country short of both professional and amateur entomologists.

“If you contrast Australia with western Europe,” Reid says, “there’s no comparison with the number of people observing insects.”

Earlier this month, David Yeates, from the Australian National Insect Collection at the CSIRO, spoke about the widespread perception among experts that insects were in trouble as were the creatures that fed upon them.

“The worry is,” Yeates said, “if insect populations are in decline, so are the populations of larger animals such as birds and lizards who rely on them as food. We know in alpine New South Wales, there’s been a collapse in Bogong moth populations – a staple food source for iconic Mountain Pygmy possums in spring, and this decline is resulting in the possums starving. But for most species these detailed interconnections are unknown.”

Assessing populations poses a particular problem in an era of ecological collapse.

In a recent article for New Scientist, Adam Vaughan notes the difficulty in keeping perspective on wildlife abundance.

He cites an anecdote from the butterfly collector SG Castle Russell who, in 1892, reported such a proliferation of insects in England’s New Forest that he could barely see ahead, with two sweeps of his net securing more than a hundred specimens.

We don’t see butterflies in swarms like that – and nor do we think that we should.

Hence the phenomenon noted by oceanographer Loren McClenachan, in which historical photos taken in Key West since 1956 show generations of anglers posing proudly with ever-smaller catches.

We adapt our expectations to the current reality, forgetting that not so long ago the natural world looked startlingly different.

“[The] big fish that used to be abundant … aren’t anymore,” says McClenachan, “and that’s happened really, really quickly.”

Many Australians don’t realise that the land near modern Melbourne once resembled, as Tim Flannery puts it, “a temperate Kakadu”, in which a shockingly blue lake teemed with swans, ducks, brolgas, magpie-geese, Cape Barren geese and other migratory birds.

Arriving in Sydney with the First Fleet, the surgeon Arthur Bowes Smyth wrote in wonderment of how “the singing of various birds among the trees, and the flight of the numerous parakeets, lorikeets, cockatoos and macaws, made all around appear like an enchantment”.

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In Hobart in 1804 the clergyman Robert Knopwood complained about the whales that disturbed locals with their bellowing and so crowded the local rivers as to make navigation by boat difficult.

Today, when Christmas beetles often appear in ones or twos, it’s difficult to grasp Grainger’s enthusiasm for their “humming”.

But in November 1936, a local paper in Maryborough reported that the scarabs had “made their presence felt” in the town, swarming in such numbers that “the noise of their whirring wings in confined spaces between buildings was like the sound of a far-off aeroplane”.

Nine years later, the Sydney Morning Herald explained that “where these gregarious pests gather their whirring fills the air and branches are quickly denuded of leaves”, before adding a sinister coda: “poison sprays and DDT are effective”.

Today, Reid blames the city sprawl for the lack of beetles, with, for example, the spread of western Sydney covering traditional habitat in the Cumberland Plain woodland with roads and new housing.

Their larvae live in the soil, feeding on roots and rotten wood until they pupate and dig their way out with their strong forelegs.

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That means they’re particularly susceptible to drought.

“We know that if the soil is too dry and hard, they just die in the pupal cells because they can’t get out.”

But Reid also sees a general decline in other species.

“When I’m out walking, I take a net with me. I’m always looking at what’s on vegetation and I’m not seeing very much. And then with the fires, you’ve got another layer on top of everything.”

But we simply don’t know how much we’re losing.

That’s why the Australian Museum offers a Christmas Beetle ID app. There’s also citizen science apps such as iNaturalist Australia, Wild Pollinator Count and Butterflies Australia, programs designed to gather more data on threatened species.

It’s an emotional time to be working as an entomologist, as the ecological diversity that once existed slips away.

“I’ve been talking about this a lot with colleagues,” Reid says. “One of the classic plants for insects in Australia is tea tree. And about this time of year, tea trees are flowing in abundance and there’s normally clouds of insects all over them. And we’re not seeing that.”