| The Question: I found this on my driveway. It doesn’t look like anything I’ve ever seen. It was about 7.5 cm (3 in.) long. What is it?
Submitted by: Debbie, Manitoba, Canada
(click on photos and graphics to expand)
The Short Answer: Debbie, this is a water scorpion, almost certainly the brown water scorpion (Ranatra fusca) because that is the only Ranatra species common in Manitoba. Water scorpions are not scorpions at all, but are actually aquatic insects, members of the order Hemiptera, the “true bugs.” Brown water scorpions are the most common water scorpions in North America and can be found across a wide area of the continent. Despite the name, they can vary quite a bit in color. They look something like walking stick insects, but water scorpions aren’t closely related to walking sticks, which are members of a different order entirely, the Phasmatodea.
More Information: Water scorpions are found in fresh water on all continents except for Antarctica. One of your excellent photos captures the wings of the water scorpion. These insects lay their eggs under water, and complete all their development under water. But they may fly to disperse from their natal ponds.
At the tail end, water scorpions have two projections that come together to form a breathing tube that the insect can extend above the surface of the water. It’s this extension that reminded people of a scorpion, and earned it the descriptive name, but water scorpions don’t have the ability to inject venom with their “tail” the way scorpions do.
In fact, if there is trouble, it’s at the other end of the creature. The modified front legs of a water scorpion are used to grab and capture prey, in much the same way that a praying mantis uses front legs to grasp prey. And it’s also at the front end that the water scorpion has a piercing mouth tube that injects venom into its prey. This venom includes paralyzing agents as well as enzymes that digest the prey’s insides, which the water scorpion then sucks out. Though there’s far too little venom to paralyze you nor allow a water scorpion to suck your insides out, the venom it injects can be painful if it gets under your skin, so it’s best to handle water scorpions carefully.
Water scorpions are “ambush predators.” They attach themselves to underwater plants and wait for suitable prey to swim by. That prey can be other aquatic insects or crustaceans, small tadpoles and fish … pretty much anything it can grab and subdue. They are voracious predators of mosquito and black fly larvae, so I hope you treated your visitor well and thanked it for all its hard work to reduce the number of bloodsuckers in your backyard.
If you watch this video, you’ll see a water scorpion capturing daphnia, tiny aquatic crustaceans. At about the one minute mark, you’ll see that this water scorpion catches a second daphnia before it has even finished feeding on the first one it catches.
Two Types of Water Scorpions: The water scorpion you found is from the subfamily Ranatrinae. The species in that group are all thin and stick-like. The other subfamily of water scorpions, the Nepinae, has a flattened, beetle-like body as shown in this photo of a species in the genus Nepa. Despite the difference in shape, the habits and hunting methods of the two groups are fairly similar.
Sources: Sites, R and Polhemus J T. (1994). Nepidae (Hemiptera) of the United States and Canada. ANNALS OF THE ENTOMOLOGICAL SOCIETY OF AMERICA Vol. 87, no. 1.
Thanks to Bugguide.net.