Discovery of black mass clinging to suburban tree stuns Aussies

The hairy caterpillar-like bugs reminded many of their childhood, who were surprised to see they still exist.

It's not every day you see a tree covered in masses of furry insects. In fact, some claim it's been 20-odd years since they last saw what was spotted in Melbourne this week.

Huddled together on a tree trunk in a suburban street was a bunch of black, hairy bugs with distinctive yellow tips — for many, a familiar and nostalgic nod to their childhood.

One Melburnian however was shocked, asking "simply... what is this?" in an online post where they shared the picture on Tuesday. The poster appeared baffled by the sight of what's often mistaken as caterpillars.

Spitfires, or sawfly larvae, on eucalyptus tree in Melbourne.
A bunch of spitfires, or sawfly larvae, was recently spotted on a tree in Melbourne. Source: Reddit

Little black grubs identified

The black grubs, however, are what's commonly known as "spitfires", which are technically called sawfly larvae, which turn into a wasp. Explaining how they got their nickname Associate Professor of Biology, Dr Darrell J Kemp, explained it refers to their behaviour.

"If disturbed they whip themselves around and regurgitate their foregut contents (usually a soupy mess of part-digested eucalypt foliage). That’s nasty enough to deter most predators I guess," he told Yahoo News Australia.

Spitfire bug or sawfly larve
When disturbed, spitfires arch their backs and regurgitate the contents of their stomach to deter predators. Source: Getty

'Haven't seen them around in years': Do they still exist?

The online post came as a surprise to many who admitted "I haven't seen these around in years". "So many childhood memories, hey. Don't see them like that, or hardly at all compared to 30+ years ago," one admitted.

Another said, "I remember seeing them all the time in the 90s. Haven't seen any since". Someone else said they swear "these things only existed in primary schools" as that's the only place they saw them. Even Dr Kemp agrees, "I haven't seen them around that much in recent decades".

Why are insect numbers dwindling?

Whether there's truth in their dwindling numbers or if we simply don't notice them like we used to, Dr Roger Farrow, an Insect and plant ecologist, suggests a reason why this might be — although we can't be certain.

Reads 'What on Earth? Australia is the only developed nation identified as a
Australia is the only developed nation identified as a "deforestation front" by WWF.

"I would say that the populations of sawflies have waxed and waned over the years due to fluctuations in the state of the environment, like those of most insects," he explained. "During the millennial drought and the severe drought of 2018-2019, sawfly populations declined like those of many other insects".

He went on to say it's "very difficult to say" whether there is a general decline in insect populations in Australia, comparable to those seen in Europe, "where conditions are very different due to extensive loss of natural habitat and intensive farming practices".

In fact, the global insect population is declining at an unprecedented rate of up to two per year, according to Reuters. Deforestation, pesticide use, artificial light pollution and climate change are said to be contributing factors.

Spitfire larvae on tree (left) sawfly on concrete (right)
Spitfires (left) develop into sawflys (right), which is a type of wasp. Source: Getty

Picture shows 'normal' spitfire behaviour

Additionally, sawfly larvae "prefer the leaves of young eucalypt trees to feed on" so without young trees to feed on, they simply won't survive. Dr Kemp suggested people might be "landscaping with less-preferred plants these days" contributing to less sightings around the country, but he's only speculating.

What we're seeing in the image shared on Reddit is "normal behaviour" by the larvae which are "probably leaving the tree to search for a pupation site where they will burrow into the ground and pupate," Dr Farrow said. This refers to the process of entering the next stage of their lifecycle.

"Later in spring the adult sawflies will emerge, mate and lay their eggs in eucalypt leaves and the life cycle will start again. The adults do not feed," he said.

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