Have you ever heard a hissing sound in the wild when dusk falls, or witnessed a dark-coloured, slowly crawling shadow resting on a tree trunk? You are lucky if you did because you have just encountered the infamous Rhinoceros beetle!
These beetles, called Brown Rhinoceros Beetles (𝘟𝘺𝘭𝘰𝘵𝘳𝘶𝘱𝘦𝘴 𝘴𝘱.), belong to the famous Scarabaeidae family (Coleoptera order). The 𝘟𝘺𝘭𝘰𝘵𝘳𝘶𝘱𝘦𝘴 genus is widespread in Southeast Asia and Oceania, ranging from south China to Queensland (Australia). In Hong Kong, these species are considered relatively large, reaching a size of 3 to 6 cm. At night, they actively seek food sources, including sap and rotten fruits. They have a sweet tooth, I mean mandible!
Equipped with a shiny body, usually black, brown or reddish, they appear carrying a full armour set. This is their exoskeleton, literally external skeleton, which covers the entire body. This rigidified exoskeleton is, however, only found in adults; with the adult stage representing only a small portion of their existence. Indeed, a Brown Rhinoceros Beetle spends most of its lifetime as a fat, white larva (also sometimes referred as grub), consuming humus, decaying or rotten wood. After half a year, these larvae enter the pupal stage, during which the individual will experience a complete metamorphosis, reconstructing its body entirely to finally emerge as an adult! This form of development is called holometabolous development or complete metamorphosis, for insects that experience the stages of eggs, larvae, pupa and adults; and with those stages showing very distinct morphological (and often ecological) characteristics.
As a glorious knight, the beetle, of course, needs a weapon to match their valor! Brown Rhinoceros Beetles, with other relatives of the Dynastinae subfamily, are insects with strong morphological differences between sexes, something known as sexual dimorphism, where males can be easily distinguished by the presence of horns on their heads and thorax. They use their horns to fight other males in more or less ritualized displays to access the females, food or in the defense of a territory. Besides fighting, the horn also aids the beetles in digging. Usually, the size of the horns is informative on the nutrient conditions the larvae experienced during their development. Greater horns and larger body-size reflect sufficient feeding as larvae.
Brown Rhinoceros Beetles also display a rather unique acoustic ability. When defending themselves against enemies, or during a battle between males, they produce a hissing noise. These sounds are not actual “screams” generated from their throats, but rather a result of the beetle rubbing its wing case to its abdomen; a mechanism similar to a grasshopper’s acoustic ability. One feature distinguishing the Brown Rhinoceros Beetle from most beetles is that the tip of their wing cases present a rough texture that feels like sandpaper, allowing them to generate a larger volume of noise！
Although these beetles look harmless, their presence is not always welcomed. Obsessed with sweets, these beetles might cause trouble to Orchards, as they might peel and consume fruits, such as lychee and mango. Yet, these are extreme cases during mass outbreaks, as normal populations usually cause limited damage to plants. But even then, their presence may be more beneficial to farmers as they act as decomposers as larvae, consuming dead woods and rotten materials, converting them into processed nutrients then available to plant growth. Ultimately, they serve an important role in the ecosystem and farmland as well, which may deserve a few fruits as wages, no?
If the life journey of our little warrior had your curiosity piqued, be sure to follow us for more amazing weekly posts and share this article with your friends! And don’t forget to take a visit to the Hong Kong Biodiversity Museum, to explore the diverging lifeforms on our Planet!
Text: Max Chan
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