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Water Scorpion Care and Habits – Aquatic Insects for Arachnid Fans

Water Scorpion with guppyOver the past several months, I’ve spent much time collecting aquatic insects with my nephew, who is quite the intense little naturalist (please see photos – I’m having as much fun as he!).  In addition to our usual haul of backswimmers, predacious diving beetles, dragonfly larvae and the like, this season I was pleased to find a healthy population of Brown Water Scorpions (Ranatra fusca).  Combining characteristics of mantids, walking sticks and scorpions, all modified for life underwater, these amazing creatures are simple to keep and fascinating to get to know.

Aquatic Insects as Pets

In years past, I set up aquatic insect exhibits for several zoos and public aquariums, but it seems that interest remains rather low among private invertebrate keepers.  This surprises me, as their range of lifestyles rivals that of their land-bound cousins, and never fails to astonish me even after all these years.  Please see this article for information on aquatic beetle care, and watch for others in the future.

Natural History 


Water Scorpions are classified in the order Hemiptera and the family Nepidae.  Members of the order Hemiptera, known as True Bugs, have sucking, beak-like mouthparts.  Examples include cicadas, giant water bugs, backswimmers, leafhoppers and aphids. Approximately 270 Water Scorpion species have been described worldwide, 13-15 of which inhabit North America.  No doubt many others are awaiting “discovery”.

Physical Description

The body of the Brown Water Scorpion resembles that of a terrestrial stick insect and is yellowish-tan to dark brown in color.  Others, including those in the North American genus Nepa, are flattened in appearance.  The front legs are raptorial (designed for grasping) and superficially similar to those of a praying mantis.  Unlike a mantis, however, the terminal segments of the Water Scorpion’s front legs fit into a groove when not in use, and swing out like folding knives when needed.  These hook-like leg tips can be seen in the photo showing a Water Scorpion poised just below a guppy.

The middle and hind legs are about as long as the body, and paired breathing tubes are situated at the end of the abdomen.  This species reaches 1.75 inches in length (to approximately 3 inches including the breathing tube).

Water Scorpions can fly, but do so only rarely.

Amazing Organs

Three pairs of disc-shaped organs on the abdomen, known as false spiracles, enable Water Scorpions to gauge water depth and compensate for changes in water pressure.


From southern Canada through much of the continental USA to northern Mexico.


Poorly adapted for swimming, Water Scorpions favor the still waters of ponds, swamps, lake edges and canals, where they remain immobile among plants and sticks.  The photo of my nephew “waiting in ambush” shows their typical habitat.


Water Scorpion predatory hooksThis voracious carnivore feeds largely upon the body fluids of invertebrates, but will also take small tadpoles, fishes and newts.  Water Scorpions are ambush predators, relying upon camouflage when hunting.  They lash out with the front legs and subdue prey via salivary fluids injected through the sharp beak.  These fluids contain chemicals that tranquilize prey and initiate digestion; food is consumed in liquid form, in the manner of spiders.


Eggs are inserted into living or dead plants, and hatch in 2-4 weeks.  The nymphs resemble the adults (incomplete metamorphosis) and mature in 4-6 weeks.

Captive Care


The aquarium should be covered and the water slow-moving.  Water Scorpions are poorly-equipped for swimming, and will perish if buffeted by strong currents.

The tank should be well-stocked with plants (preferably live) and sticks that rise to the water’s surface.   Water Scorpions breathe by extending the abdominal breathing tubes above the water’s surface, and cannot utilize oxygen dissolved in the water. They will not thrive if unable to station themselves on a plant or stick near the water’s surface.

Filtration and Water Quality

Water Scorpions may be kept in an unfiltered bowl, jar, or aquarium if provided a weekly water change (please see photo of my simple enclosure).  Live plants will enhance the aquarium’s appearance and assist in maintaining water quality.  If filtration is desired, be sure to avoid strong water currents.  Sponge, undergravel, and corner filters are ideal.

Although Water Scorpions inhabit waters that are often subjected to varying pH and ammonia levels, water quality should not be ignored. In this regard, they should be maintained as are tropical fishes (please write in if you need further information).  Water used in the aquarium should be treated with chlorine/chloramine removal drops and maintained at pH 6.8-7.2.

Light, Heat and Water Quality

Temperatures of 65-82 F are well-tolerated.


Water Scorpions are attracted to prey by movement, and will take small crickets and bits of fish, shrimp and earthworm from tongs.  I also offer small guppies, mosquito larvae and blackworms.  I’ve not seen them take smaller prey items, but mosquito larvae do disappear (and seem not to be buzzing about the house!).

Compatible Species

In common with many aquatic insects, Water Scorpions will consume smaller individuals of their own species.  However, as captive breeding seems not to have been recorded, keeping several in a well-planted aquarium would be worthwhile (reduced temperatures and a shortened light cycle in winter may encourage reproduction).

These slow, deliberate hunters will not get enough food in aquariums housing diving beetles, water boatmen, fishes and other aggressive feeders.  In such situations, they must be individually fed via tongs.

Captive Longevity

Adults over-winter and can live for 2 – 2.5 years.


Child with Water ScorpionAs you can see from my 4-year-old nephew’s smiling face, Water Scorpions are rather “stiff” and cannot bite if held as illustrated.  The long beak seems quite formidable, but several observers report that it cannot pierce human skin (this re Brown Water Scorpions; others not mentioned).  I’m wary of aquatic insects, however, as even the smallest predatory species can usually inflict a painful bite.  After so many decades of being bitten and stung by creatures large and small, I have no desire to experiment!  I advise that you handle via tongs or a net.

What Can I Do?

Insects and other invertebrates occupy every conceivable aquatic habitat, from birdbaths to swamps and even the sea.  Running a net or small strainer through just about any bit of available water will yield a treasure trove of interesting creatures, many of which are quite easy to keep and even breed.  So get out there and look around, and please feel free to write in with suggested topics, so that I can cover your favorite species.



Further Reading

 Diving Beetle Care

Video: Australian Water Scorpion

Water Scorpion Natural History and videos

Insect Families in the Order Hemiptera

Crickets and Carotenoids – Study Examines Cricket Nutrient Levels

veggiesCaptive insect-eating reptiles and amphibians (and perhaps invertebrates) are often plagued by nutritional deficiencies. A highly-varied diet is a great way to ensure adequate nutrition, but most keepers have access to only a few feeder-insect species; gut-loading (providing nutritious diets to feeders) is helpful, but detailed studies are lacking. While touring several Japanese zoos a few years ago, I was intrigued by the number of cricket species being bred as herp food, and resolved to investigate the species and diets I saw in greater detail. A recent article in Zoo Biology (2011, V. 30), which provides insights into carotenoid supplementation in three different cricket species, has re-sparked my interest. I’ll summarize below.


Carotenoids are pigments that occur in plants. Animals, as far as is known, cannot manufacture carotenoids but rather must obtain them through their diet.

Carotenoids benefit the immune system by acting as antioxidants, function in the reproductive and other systems, and are believed partially responsible for the health benefits enjoyed by people who regularly consume fruits and vegetables.  We know little of their role in reptile and amphibian health, but many zoo nutritionists believe them to be important. Read More »

“Dangerous” Insects and Invertebrates…and Why We Need Them!

Robberfly with PreyIf insects were to vanish, the environment would collapse into chaos”.  Expounding on this statement, noted entomologist E. O. Wilson went on to explain that, without insects and other invertebrates (animals without backbones), all life would grind to a halt.  Yet while many pollinate plants, provide us with medicines and are otherwise helpful, others are dangerously venomous, spread disease, and consume valuable crops.  But as we’ll see, harmful invertebrates are in the minority, and even they hold secrets that can be of immense value to humankind.

Astonishing Diversity

Mammals, birds and other well-known vertebrates comprise only 5% of the world’s animals…the balance is made up of insects, spiders, crabs, mites and an unimaginable diversity of other invertebrates.

Estimated at 30 million species, insects are the largest invertebrate group.  To put their numbers in context, consider this – the weight of insects in most African rainforests exceeds that of all resident vertebrates combined!  This statement takes into account such huge mammals as forest elephants and gorillas, and the incredibly numerous bats and rodents!   Insects are abundant outside the tropics as well – an acre of Pennsylvania soil may hold 425 million individuals, while New York is home to over 4,125 beetle species.  Read More »

Amphipods (Scuds, Side-Swimmers) as Food for Amphibians and Reptiles

Gammarus Roeselii (Scud)Like sowbugs (isopods, pillbugs), Amphipods are crustaceans that feature prominently in natural diets of many reptiles and amphibians.  They contain nutrients not found in insects, and are likely a rich source of calcium.  Several species are easy to collect and breed in captivity, but, unlike sowbugs, they rarely attract much attention from hobbyists (please see the article below for information on breeding sowbugs).  Whether you know them as Rock-Hoppers, Sand-Hoppers, Lawn Shrimp or any of the names above, one Amphipod or another likely makes its home near yours, and may be worth investigating as a food source for your pets.

Natural History

Amphipod diversity is astounding…over 7,000 species have been identified, and experts concede that they have no idea of the actual number in existence.

Found from pole to pole, Amphipods reach their greatest abundance in colder oceans.  Most live in marine environments, but a number have colonized fresh water and land; of the known terrestrial species, 45% dwell in caves or other subterranean environments.  They range in size from 0.8 to 1.6 inches long, and may be omnivorous, carnivorous or herbivorous. Read More »

Ant Control for Reptile and Amphibian Owners – Diatomaceous Earth

AntsDrawn by uneaten food, shed skins and other organic material, ants sometimes become pests around reptile, amphibian and invertebrate collections. As pesticides are harmful to humans and other creatures alike, eliminating ants in areas used by pets and people takes some care.  Today I’d like to highlight a substance that I used with great success in various zoos, and which works equally well at home – diatomaceous earth.

A Most Formidable Insect

Famed entomologist E.O. Wilson has demonstrated that ants “rule” many habitats, driving evolution and other processes to a degree that is hard to imagine.  What little work I’ve done with them has convinced me that they are, at the very least, extremely resourceful creatures. When working with Leaf Cutter Ants (Atta cephalotes) at the Bronx Zoo, I observed a dramatic increase in egg production shortly after empty nesting chambers were added to the colony’s enclosure – the workers somehow communicated to the queen that more space was available, and more bodies were needed. This likely holds true for other species as well – killing a few dozen workers will not reduce ant numbers but instead may set up a call for more eggs! Read More »

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