Specimen Showcase｜Underwater Chimera
- Hong Kong Biodiversity Museum
- 6 days ago
- 4 min read
In the serene realms of freshwater habitats, where still waters whisper tales of hidden predators, one enigmatic creature reigns with its stealth and prowess. The elusive 𝘙𝘢𝘯𝘢𝘵𝘳𝘢 𝘤𝘩𝘪𝘯𝘦𝘯𝘴𝘪𝘴 (Mayr, 1865), commonly known as the Chinese Water Scorpion, conceal themselves underwater, and when a prey swims in front of them… snatch! Another fish goes down to the swift water scorpion🦂. Apart from water scorpions, they are also called water stick insects, or water mantis. What is the identity of this mysterious animal?
Water scorpions get their name from the long “stinger” they have at the end of their abdomen. However, the water scorpion is not a scorpion, but an insect. To the careful observer, one will note their 3 pairs of legs and a pair of stiff wings, granting them the ability to fly🦋. Their “stinger” is also not a stinging appendage, so don’t worry. This appendage actually serves a very important purpose: breathing. Water scorpions spend most of their lives staying underwater, but they don’t have gills to breathe underwater. This “stinger” is in fact called a siphon, and is composed of two half-tubes which, when joined, function as a kind of snorkel🥽, getting air above water. The water scorpion rests hind-end up and has the siphon tip protruding above the water's surface, allowing them to remain submerged for extended periods of time.
Now we know the water scorpion is an insect instead of a scorpion, we still need to know if it is a stick insect, a praying mantis, or something else? With its elongated body, thin six legs, and a long and thin siphon, the water scorpion could be confused for a stick insect, a group of insects mastering disguise and blending seamlessly with sticks in a mesmerizing display of camouflage. But, no, water scorpions are not stick insects (Phasmatodea). They present several major ecological differences, with stick insects being mostly arboreal animals🌳, while water scorpions live underwater💧. Also, stick insects are herbivores, while water scorpions are carnivores, eating other insects, fish and tadpoles underwater. Though they are not stick insects, they get similar benefits for mimicking a stick. Water scorpions like to live around aquatic plants, which they can cling on and allow them to stay close to the water surface to breathe. They can also apply their brilliant camouflage at its finest. Their camouflage doesn’t just help them hide from their predators, but also their prey, making them a perfect ambush predator.
Praying mantis could thus appear as a potential alternative. After all, they are famous ambush predators, and the water scorpions share other similarities with them. Like mantis, water scorpion’s forelegs are modified just like those of mantis, which are specialized for grasping prey, leaving both insects two pairs of legs to walk. Both use their camouflage to blend in the environment, waiting for the perfect timing to catch their prey. Although water scorpions are highly similar to mantis, they belong to two distinct groups of insects. The first difference they have is once again, mantis are terrestrial animals, while water scorpions are aquatic animals. The eating behaviour of the two insects is also different. After catching the prey with their forearm, mantis will use their strong mandibles to bite and chew. For water scorpions, they don’t have mouthparts that can help them bite or chew, but a rostrum, a tubelike structure that water scorpions can use to pierce into their prey, injecting a saliva to first sedate💉, second, digest the prey. At last, the digested prey will be liquified and sucked out.
So, if a water scorpion is not a scorpion, stick insect or a mantis, then what is it? To figure out its proper classification and thus closest relatives, we need to investigate their mouthparts. The rostrum in water scorpions is a type of mouthparts commonly found in an order of insects called Hemiptera, the true bugs. This is one of the most diverse orders of insects, with about 90000 species described. True bugs can be both terrestrial and aquatic. One of the aquatic true bugs was already introduced in a previous specimen showcase: the giant water bug > https://bit.ly/48XgmSl . The water scorpion is a related species both belonging to the same group called Nepomorpha, which include several aquatic hemiptera.
Does the water scorpion raise your interest in ecology and biodiversity? If your answer is positive, come to the Hong Kong Biodiversity Museum where we have a wide variety of specimens, from sponges to bats, and you can learn more about their fascinating ecology. If you found this article📝 engaging, share it with your friends and stay tuned for our captivating biodiversity narratives released weekly!
Text: Paco
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