Water Scorpion

Water Scorpion

Habitat: Long Island; Death Valley 
Type: Large Aquatic Insect
Length: 10 to 12 Inches (body), longer with breathing tube
Weight: 1 to 2 Pounds

Water Scorpion Using Its Tail Snorkel

The Water Scorpion is one of the largest animals found in the narrow river that runs through Death Valley. In a place where most creatures are built to scavenge, this is a true predator. It moves slowly through the shallow water or along the muddy bottom, often blending in with sticks and debris. When still, it is easy to miss, especially in the dim light of the canyon.

Its body is long, broad, and flat, with a pair of folded front legs shaped for grasping. These two front legs are tipped with dark, hooked claws. The front limbs are held out in search of prey, and then snapped shut when that prey comes within reach. The rest of its legs are used for slow movement rather than swimming, and it does not move quickly unless it is striking. Most of the time it remains still, waiting for something to pass within reach.

At the rear of the body is a long tail-like tube. This tail is held up to the surface when it is submerged, indicating that it could act like a snorkel. When it leaves the water, the tail hangs straight behind it instead of being held upright.

Leaving The Water

The Water Scorpion feeds on nearly anything it can overpower. It regularly grabs Piranha Divers and Giant Purple Leeches, both of which share its river habitat. It will also hunt along the edges, reaching out of the water to grab animals moving along the banks, like an insect's version of a crocodile. Carnivorous Beetles, Valley Tarantulas, and Silver Spiders are all taken this way. 

Younger Water Scorpions are vulnerable and are often killed by the same creatures that adults would consider prey. Purple Leeches and Valley Tarantulas are common predators of immature Water Scorpions. As the animal grows, though, this changes. A full-grown Water Scorpion is too large and too well-armed for these lighter predators to handle, and it becomes one of the dominant hunters in the river.

The only threat to an adult comes from the Parasitic Wasp. This wasp does not actually feed on the Water Scorpion itself, since it is an herbivore in its adult form. Instead, pregnant females land on the Water Scorpion (when it leaves the water or gets too close to the surface) and inject their eggs directly into the body. Once inside, the larva develops quickly by ravenously feeding on the living animal. This eventually kills the host before the larva emerges as an adult wasp.

Parasitic Wasp Injecting Its Larva

• Naturalist Note: The Water Scorpion described here is likely a member of the genus Nepa, a group of aquatic true bugs (order Hemiptera) also known as "toe biters." These bugs possess raptorial forelegs and a caudal breathing siphon. Though Daniel is correct in his assumption that this siphon is used in breathing, he incorrectly calls it a "tail." Also, known Nepa species possess two separate caudal siphons, but Daniel describes the Water Scorpion as having a single "tail." It is unclear if he was mistaken in that description, or if this species possessed fused siphons.
  
  The breathing tube allows the insect to remain submerged indefinitely. This adaptation supports the ambush strategy noted in the field observations. The forelegs are homologous to those of mantises in function (though not relation), capable of rapid extension to seize prey. It appears that the forelegs in this species taper to dramatic-looking claws.
  
  Its diet, including large annelids (the Purple Leech), beetles, and arachnids, is consistent with a generalized predatory hemipteran, though the ability to subdue such comparatively large and sometimes dangerous prey suggests a potent salivary toxin and strong mechanical grip. The apparent avoidance of carrion is notable, as many large invertebrates in nutrient-dense but competitive systems adopt opportunistic scavenging; this species appears to remain a strict predator.
  
  The described parasitic wasp interaction is particularly significant. Large aquatic hemipterans are known hosts to parasitoids, but the successful parasitism of such a large and well-defended insect implies either highly specialized oviposition behavior or a biochemical adaptation that suppresses host defenses.