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28 Dec 2017

Summer is here, and so are the cicadas

Dr Nathan Emery is a plant scientist at the Australian Botanic Garden with an unusual weekend hobby - cicada research. Nathan's whole family is into cicadas. His sister even has a species named after her. Cicadas have been particularly loud around Sydney this summer so we asked Nathan to tell us a bit about them. 

I am a plant ecologist with a poorly kept secret – I love cicadas! Indeed, I spend many of my summer hours outside of work time at the Australian Botanic Garden undertaking personal research on our noisy invertebrates. If I count back to the summers spent helping my dad catch cicadas in bushland areas around Sydney, I can safely say I have over 20 years of experience working in cicada research!

Why cicadas? Because they are so diverse, and yet there is so much we don't know about them. Australia has the highest number of species in the world, and it seems outrageous to me that we know little or nothing about their ecology, or that species have not yet been described. I also love them because they are a way to reconnect people with nature.

 I believe that one of the main attractions of cicadas comes from an intrinsic point-of-view. They capture the imagination of humans like no other invertebrate. Their sudden emergence, marked by the appearance of empty nymph casings and their loud noise make them impossible to ignore over summer. Common names like the Masked Devil, Candy Tiger Squawker, Desert Screamer, and Sandgrinder create a sense of curiosity. Almost everyone that I speak to has a story or two to tell about cicadas from their childhood. Their presence is a reminder of the nature we have around us.

Ten fascinating facts about Australian cicadas:

  1. Australia is the cicada capital of the world with a predicted 700-1000 species. North America has around 170, South Africa around 150, and only 1 species in the UK. Only around 350 Australian cicada species have been scientifically described.
  2. A cicada begins its life as a nymph living underground in the soil and feeding off the sap from roots of a plant using a long proboscis (a feature of all sap-sucking bugs – Hemiptera).
  3. There is no concrete evidence that details exactly how long a cicada spends underground. Anecdotal evidence suggests it to be somewhere between 6-10 years, depending on the species.
  4. It was scientifically demonstrated in North America that cicadas can count seasons by detecting changes in xylem flow (plant root fluid).
  5. We don’t know what specific conditions trigger their emergence. Cicada nymphs do emerge in the warmer months, especially as overnight temperatures increase. A rainfall event prior to emergence is also important.
  6. Adults typically live for one to four weeks and feed on the sap of soft-wood branches. Their sole purpose is to find a mate.
  7. Males call to females in attempts to attract them, and the call-song is unique for each species. For larger species, such as the Green Grocer, Double Drummer, and Cherrynose, males sing in synchrony (termed a cicada chorus), and females will fly to the males. This calling strategy also deters predators due to the sheer volume of sound produced.
  8. The main predators of cicadas are birds, but also other invertebrates including spiders and robber flies.
  9. Cicada season in Sydney starts in September and can continue through to April/May. The noisiest months are November to January.
  10. The Hairy Cicada (Tettigarcta genus) – Australia’s oldest cicada genus that dates back to the Jurassic period – is incapable of singing. Males communicate through vibrating the substrate. Hairy cicadas also produce a thermal reaction to create heat that allows them to survive cold temperature in Victoria and Tasmania.

The rich cicada diversity in Australia reflects the wonderful plant biodiversity we find in our environments – from the coastal heathlands to the central arid dunes. This is because cicadas have particular food plant preferences. From survey work undertaken in the Cumberland Plain Woodland in western Sydney by myself and Dr Alan Kwok, we know that different vegetation communities support different cicada communities. And this holds true even when the vegetation communities are adjacent to one another.
Because cicadas are periodical in their emergence, gaining an understanding of their distribution and emergence patterns requires long-term data collection. In this sense, the role of amateur naturalists and citizen scientists is a crucial element for recording data. Cicadas are an excellent focus for citizen science projects as they can be abundant in the urban areas of Sydney.
To this end, I recently set up a citizen science project called ‘The Great Cicada Blitz’ on the iNaturalist website. It’s free to sign up and add observations of cicadas in your local area. You can download the app and record sounds or photos with your observations. Surveying them only requires a bit of practice, a keen pair of ears and a recording device such as a smartphone.

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