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Scavenger Crustacean - Water Scorpion Scavenger Crustacean

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Water Scorpion Scavenger Crustacean



Ranatra fusca


If you’ve ever wanted something unusual to look at in your freshwater tank, this is probably it!  Simple to care for, hearty, easy, and hard to kill!  This is a wildly unique, stick-bug-looking animal!  Water scorpions are not really scorpions, but insects with only 3 pairs of legs and 2 pairs of wings.  The forelegs of the water scorpions are adapted for grasping prey, but lack pincers; instead, they use a jack-knifing design with the outer segments folding into a groove to secure prey.  The tail does NOT sting, nor is this a venomous animal.  The tail is used to obtain air from the water surface, much like a snorkel.


The water scorpions belong to the insect order Hempitera, or the true bugs. Like all hemipterans the head is a long sucking beak or rostrum, which conceals the mouthparts.  The head of a water scorpion is very small and the rostrum projects forward.  The large eyes project to the side.  The Hemiptera are insects that grow through a series of molts but lack a distinct metamorphosis. The juvenile stages, or nymphs, resemble small versions of the adult.


Like all insects, water scorpions possess antennae (feelers), but they are tiny and lie concealed at the base of the eyes.


There are nine different species found in North America, but they are difficult to identify.  The most common species in our region is the pale buff Ranatra fusca.  Ranatra are pale buff in color.  Adults will fly on warm days, lifting the wings to reveal a red-topped abdomen.  These slender insects are fairly common and widespread in slow-flowing waters with dense vegetation.  Adults are 1.2 to 1.4 inches (30-35 mm) long with a 0.4 to 0.6 inch (10-15 mm) 'tail.'



Ranatra fusca appears to be widespread in the Southern US, though seldom abundant.  There is little information available on other species.  Water Scorpions are quite tolerant of polluted and deoxygenated waters, but are usually associated with dense vegetation.  Nymphs occur in the summer months, but adults may be found throughout the year. 


Natural History

Water scorpions usually lurk motionless close to the surface, head down, clinging to twigs or aquatic plants.  Periodically, they back up to the water surface to replenish air.  Like the majority of insects, water scorpions are air-breathers.  They carry a submerged air bubble that serves as a renewable air supply.  Air is trapped by tiny water-repellent hairs on the under surface

of the forewings and the underlying abdomen .  The trapped air bubble connects with the surface through a series of hairs between the two tail filaments of the breathing tube.  Their slow movements and excellent camouflage make water scorpions inconspicuous to potential prey species. These include smaller insects such as the nymphs of mayflies, stoneflies, and water beetles, crustaceans such as freshwater shrimp and hog lice (Isopoda), and small segmented worms.  Water scorpions are ambush predators and cling to plants with the second and third pairs of legs. The forelimbs are held out at the front.  When prey approaches, the hindlimbs straighten, swinging the water scorpion forward, and the victim is grasped by one of the forelimbs.  Firmly held in the jack-knifing grip, it is then pierced by the rostrum and injected with digestive enzymes.  However, despite allegations in many texts, water scorpions are docile and are quite safe to handle.


Water scorpions can swim for short distances but seldom do so unless disturbed.  When swimming, they use alternating oar-like movements of the second and third legs to propel themselves in a somewhat jerky fashion.


Reproduction:  Occurs only once a year.  Males attract females by a quiet chirping, rather in the manner of a cricket.  After mating, the female lays several eggs, which are attached to aquatic vegetation.  Frequently, the eggs are inserted into the stems of emergent plants.  Eggs hatch in early summer into nymphs.  These pass through five molts before maturation.


They are easy animals to maintain in an indoor aquarium or pond.  Use a gravel bed and freshwater or pond water with plenty of submerged vegetation (Elodea, Myriophyllum, Ceratophyllum or Potamogeton are ideal).  Make sure that some vegetation reaches to within an inch or so of the water surface allowing the water scorpions to breathe.  Small nymphs and crustaceans provide ideal prey items.  Water scorpions will filter feed on tiny organisms that will pass through the water and also will feed on some of the smaller food like NLS Crustacean Formula Foods.


Conservation Measures

There are no restrictions concerning the collecting and keeping of aquatic insects.  For this reason, and because they are so easy to keep, they make ideal creatures for classroom study.


Reference: Dr. Jonathan Wright, Biology Dept., Northern State University, Aberdeen, SD. 1997
SIZE AT SHIPPING - WILL VARY BUT ABOUT 1.5 - 2" Long.  WIll ship perfect!  Extremely Tough!

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