Specimen Showcase | Giant Water Bug: A Ninja Underwater
- Hong Kong Biodiversity Museum
- Mar 10
- 3 min read
When we hear the term “true bugs”, we may immediately connect it to those stink bugs (the Pentatomidae family) which are well-known for sucking the juice of plants and the pungent smell they release when disturbed. However, with approximately 40,000 species of true bugs (Heteroptera sub-order), a wide range of ecologies, habitat uses and diet can be found in this group of insects.
Among them, the giant water bugs (family Belostomatidae) are definitely worth an introduction. As their name indicates, they have a relatively large size and are aquatic predators with over 150 species described throughout the world. They are found mostly in freshwater habitats such as rice fields, marshes, ponds, lakes, and rivers. Some of them, including 𝘓𝘦𝘵𝘩𝘰𝘤𝘦𝘳𝘶𝘴 𝘪𝘯𝘥𝘪𝘤𝘶𝘴 (Le Peletier & Serville, 1825) which measure up to 8 cm, have also been recorded In Hong Kong.
The large size of the giant water bugs is particularly useful when it comes to capturing their prey; which can occasionally even include some small vertebrates. Within freshwater ecosystems, water bugs can be seen as some of the most voracious predators feeding on numerous insect species, but also some crustaceans, small fishes or tadpoles. Species of the Lethocerinae subfamily, which include the largest species of water bugs (up to 12 cm) will commonly, as adults feed on fishes, anurans (i.e., frogs and toads), turtles and even snakes! The large body size of water bugs combined with their aquatic lifestyle provides great conditions for fossilization to occur. As a result, fossils of the giant water bugs (Belostomatidae) have been dated from the Upper Triassic or 210 M years, while those of Lethocerinae species are known from the following period of the Jurassic (145 to 200 M years)! So these aquatic predators have been roaming the waters for a long time.
Despite being large themselves, water bugs capture prey larger than their own body. How do they achieve such a feat? In fact, their unique body parts make them one of the top predators in freshwater habitats. Water bug species possess specialized raptorial forelegs for capturing prey, while some members from the Lethocerinae subfamily also present a highly curved claw on the terminal segment of their forelegs allowing them to catch larger vertebrates. Besides, their paddle-shaped middle and hind legs are fringed with hairs which help them to propel them into the water, making the water bug a very strong swimmer🏊. But their favourite attack mode is through ambush. They hide within the submerged vegetation, camouflaged thanks to their brown body colour while expanding their raptorial front legs to seize the prey with incredible speed passing in front of them. Once the prey is grasped by their front legs, it is pierced with their rostrum (the modified mouthparts) which act like a dagger and a straw to suck up the juice and life of their victims. The feeding action is helped with the injection in the prey body of saliva that contains various enzymes and neurotoxins. As a result, the prey is liquefied and eventually sucked out in a process called external digestion.
Besides this amazing feeding behaviour, these voracious predators are well-known for the display of unusual reproductive behaviour and specifically the investment of males in the protection and development of their offspring, known as paternal care. In order to maintain good oxygen and humidity conditions of their egg masses, Lethocerinae males (also called “emergent-brooders”) supply water to the egg mass, previously laid by a female on the emergent vegetation above the water surface. The eggs are usually placed in conspicuously vertical rows from 8-15 cm high on several grass blades or stems that are held together by the egg mass. In other species, the males simply carry the eggs on their back until hatching of the nymphs, providing protection against eventual predators.
At the HKBM, we have two species of giant water bugs, and the one pictured here is 𝘓. 𝘪𝘯𝘥𝘪𝘤𝘶𝘴 which has been recorded in Hong Kong. As their Chinese common name suggests, 田 tin4 (paddies) is an important habitat for this species to prey and reproduce. However, due to the loss of rice paddies in Hong Kong, they are now being regarded as a rare species. Come to the HKBM to observe these voracious and loving insects.
Text: Jacky Sung
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