The deafening soundtracks of Australia's cicadas
The siren of summer is in full swing in Australia with the song of the cicada reverberating across backyards, parks and bushland.
RISING WITH THE heat at dawn and making their "voices" heard right through to dusk, warm days are literally bookended with the call of cicadas. It can be a deafening soundtrack too, with the insects holding the record for being the loudest in the world.
A summer song
It's the quintessential seasonal sound we've come to love but sometimes the song of the cicada is difficult to bear. Large species, such as the common greengrocer (Cyclochila australasiae), can produce a noise in excess of 120 decibels at close range, according to the Australian Museum. That reach is at the limits of what the human ear can withstand, which explains why sometimes the cicada drone feels deafening. It's a powerful tool against predators but mostly a love ballad.
“Their noise can become so loud that it irritates birds and they won't fly into the tree," says entomologist Dr. Max Moulds.
Nicknamed Australia's cicada expert, Dr. Moulds says only big cicadas living in congregations can use the call as a defence mechanism, and that's a small percentage of the species, with cicadas mostly solo insects. The sound, primarily, is a mating call.
Among small species of cicadas, the male sings and the female flicks her wings in response. The male then flies to the female to mate. Among big cicadas it's the female that travels to the male, and when they're close they make more sounds prior to mating.
It's the males that make the loudest calls, with a thin drum-like membrane and hollow abdomen that amplifies their clicking sound. But this is the rule, not the exception. Some males, such as the hairy cicada (Tettigarcta tomentosa and T. crinita), don't make sound at all. Dr. Moulds, author of Australian Cicadas (1990), says the hairy cicada is a primitive species now only found in Australia. Related to leafhoppers, the male hairy cicada cannot create airborne sounds. These males have poor tymbals (the corrugated membranes in the abdomen) but can make vibrations that are transferred through their body onto the limbs of trees. Females can also do this, and so the species communicates this way, just as leafhoppers do.
The Aussie cicadas
Growing up in Australia, it was common to collect the exoskeletons of cicada nymphs left clinging to gumtrees. If you were lucky enough to find the cicada itself, it was highly likely the beautiful greengrocer or the striking black prince. As an adult then, you may be surprised to learn there are approximately 280 named species of cicada in Australia, with Dr. Moulds estimating the total number of species at around 800.
"Australia is one of the world centres of biodiversity for cicadas," he says.
The majority of Australian cicadas belong to the Cicadidae family, with the greengrocer and black prince (Psaltoda plaga) among the most well-known. There is also the redeye (Psaltoda moerens), another black cicada; double drummers (Thopha saccata), which have a copper hue and are one of the largest native species, growing up to 15 centimetres wingspan; and floury bakers (Aleeta curvicosta), which are coated in a white powder. Like a lot of Australian wildlife, we also have a few "odd-looking" species, including the endemic bladder cicada (Cystosoma saundersii), with a swollen abdomen and green, opaque wings that look like leaves. Cicadas live right around Australia but are essentially tropical insects, "so the further you go away from the Equator the fewer the species", says Dr. Moulds.
"Australia as a continent probably has more than any other continent," he adds.
A fleeting adulthood
Cicadas spend most of their life underground as a nymph, with the timeframe depending on the species. The greengrocer lives for approximately six years, however only the final six to eight weeks of its life is as an adult above ground. Other species, such as the yellow sugarcane cicada (Parnkalla muelleri) have an annual life cycle and will spend about 11 months underground. When cicadas transition from nymph to adult their skin splits and they emerge over about two hours. This leftover brown exoskeleton is what children love to collect, and what sparked Dr. Moulds' fascination with the insects as well.
The cicadas' adulthood is fleeting, given that they may only live above ground for a few days before they become a meal for an insect-eating bird. They also frequently get caught in the webs of common spiders, such as the garden orb weaver, and are preyed upon by bats, wasps and crickets. Much of their life, under and above ground, is spent eating the sap of plants and trees (often eucalypts), especially when the weather is hot, explains Dr. Moulds.
"They have to go through vast quantities (of sap) to get a little bit of nutrient."