Nature is full of sounds, especially during the hot season. Some, however, are more distinct to our ears and you are probably familiar with the loud sound produced by the buzzing and chirping of cicadas. At first, this may not appear as the most harmonious sound, but for a female cicada it acts as a serenade❤️. These mating calls are produced by thousands of male cicadas which rapidly vibrate their tymbal, a drum-like plate located on the side of their abdomen in the hope of attracting captivated females. The songs can reach up to 100 decibels, as loud as a motorcycle🏍️! Quite impressive for a 2 cm long insect. One cicada species native to Hong Kong is the brightly coloured 𝘏𝘶𝘦𝘤𝘩𝘺𝘴 𝘴𝘢𝘯𝘨𝘶𝘪𝘯𝘦𝘢 (De Geer, 1773), or black and scarlet cicada. It is distributed all over South and Southeast Asia, ranging from India to Taiwan and Singapore.
In Hong Kong, its performance happens yearly starting in May, when the cicadas pour their life and soul into their song, dying not long after reproducing😵. Their nymph (larvae) will then spend the following year underground, usually feeding on sap from plant roots, before emerging and moulting into their adult forms, gaining their wings and sound producing organs in the process.
So how can cicadas sing so loudly? Many other insects like grasshoppers and crickets produce their calls by stridulation, which means textured body parts like wings are rubbed together to produce sound🗣️. Cicadas are unique as their tymbals don’t produce sound by stridulation, instead the vibrations from their tymbals are amplified by their trachea, which are the airways insects use to breathe. This way, their entire bodies act as resonance chambers, and this unique method of vocalization allows them to be the loudest insects in the world📢.
𝘏𝘶𝘦𝘤𝘩𝘺𝘴 𝘴𝘢𝘯𝘨𝘶𝘪𝘯𝘦𝘢 stands out among other cicadas for its bright red-and-black colouring. This type of colouring, that is frequently encountered in various animal groups, is called aposematism or “warning colours”⛔️. Instead of using its colour as camouflage to hide itself, warning colours tell predators that the animal is poisonous or foul-tasting. Indeed, Huechys cicadas contain a toxic compound that also has anti-cancer properties, resulting in their use in traditional Chinese medicine💊.
The vocalizations in the cicada family are quite unique among insects, but Cicadidae possesses other interesting features. The texture observed on the surface of their wings have waterproof properties, but also antibacterial properties🦠! They have nanoscopic pillars so small and sharp that they puncture and kill bacteria, making their wings germ-proof. Though many animals secrete antimicrobial chemicals, this form of mechanical protection is uncommon in animals. This inspired scientists who are now trying to replicate this neat trick from the cicadas to produce antibacterial materials for medical equipment🩹; a case of bioinspiration.
Cicadas in Hong Kong have annual cycle with yearly emergence, but in North America some cicada species of the genus 𝘔𝘢𝘨𝘪𝘤𝘪𝘤𝘢𝘥𝘢 spend over a decade as nymphs, and emerge as a synchronised brood every 13 or 17 years. Several hypotheses have been proposed to explain this phenomenon🧐. One such explanation is that this massive, infrequent and unpredictable amount of food available to predators overwhelms them as they are unable to eat all the cicadas, making individual nymphs more likely to survive until adulthood and reproduce, ensuring the reproductive success of the species👍.
Next time you see or hear these peaceful but loud herbivores, don’t hesitate to observe them, but until the weather gets warm enough for them to emerge from underground, come see our specimens at the Hong Kong Biodiversity Museum!
Text: Elgar
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