Bug o’the Week – Wetland Homage IV – Water Scorpions by Kate Redmond

Bug o’the Weeku
by Kate Redmond

Wetland Homage IV Water Scorpions

 Howdy, BugFans,

If wetlands are the transitional spongy/submerged/semi-submerged/sometimes-submerged areas between high ground and deep water, what might some wetlands look like?  Swamps are wet woodlands, while marshes are wet areas with standing water whose vegetation is mostly non-woody.  Peatlands like bogs, which have no sources of water other than precipitation and run-off, so water stalls there and becomes acidic; and fens, which are fed by springs and are often alkaline.  And then there are sedge or wet meadows, scrub/shrub thickets, and more (for more info, see https://dnr.wisconsin.gov/topic/Wetlands/types.html) and https://www.wisconsinwetlands.org/learn/about-wetlands/wetland-types/.


The long (about 2” not including the “tail”), lean, well-camouflaged Brown Water scorpion (Ranatra fusca) is in the order Hemiptera, and thus, it can legally be called a “bug.”  It’s in the family Nepidae, which includes about 13 species in North America and 270 worldwide, including some broader-bodied species like https://bugguide.net/node/view/2205541/bgpage and https://bugguide.net/node/view/818188/bgpage that resemble the Water scorpion’s distant cousin, the Giant water bug https://bugguide.net/node/view/1657638/bgimage

Water scorpions have simple/incomplete metamorphosis, looking when they hatch pretty much like they will as adults, adding a few parts (the wings and the “naughty-bits”) as they molt (five times) and mature.  As is typical with insects that practice simple metamorphosis, both the adult and the immature water scorpions live in the same habitats – muddy-bottomed ponds and very slow streams with submerged vegetation – and both dine from the same menu.  What’s sauce for the goose is sauce for the gander.

They hang out, usually head-down https://bugguide.net/node/view/1682158/bgimage, on aquatic vegetation and in the detritus just off-shore, gripping with their second and third pairs of feet, legs bent.  Their passage through the water is sloth-like, and swimming, also using their second and third pairs of legs, is not their forte.  In fact, in A Guide to Common Freshwater Invertebrates of North America, author J. Reese Voshell, Jr. says that water scorpions are so sedentary that not only do algae and micro-invertebrates form colonies on them, but other aquatic insects may deposit eggs on them!  This immobility is part of their “stealth” hunting tactic.  

They’re equipped to fly https://bugguide.net/node/view/126649/bgimage, and fly they do, but not often, and almost always at night (say most – but not all – sources), and they must emerge and spread and dry their wings before take-off.  They are known to bask in the sun.

Despite their resemblance to the terrestrial, vegetarian walking sticks https://bugguide.net/node/view/1874213/bgpage, water scorpion are carnivorous, ambushing aquatic invertebrates like daphnia, seed shrimp (ostracods), backswimmers, water boatmen (a favorite), and even tiny fish fry and tadpoles.  They spot their prey with protruding compound eyes https://bugguide.net/node/view/1679712/bgimage, “lunge” at it by straightening their legs suddenly (without letting go), nab it with mantis-like front legs, stab it with a short beak (which is capable of piercing human skin, so handle with care), and inject it with tranquilizers and tenderizers.

Two long filaments on their south end are not stingers, but they explain the “scorpion” part of the name.  These lock together to form a breathing tube, the tip of which the bugs position just at the air-water interface.  Oxygen seeps down the tube and is stored as a bubble under the fore wings, against the abdomen.  They can use that bubble of air when they want to go deeper than their “snorkels” will reach (the structure of the filaments doesn’t allow water to enter), and in well-oxygenated water, oxygen suspended in the water can diffuse into the bubble, giving the insect extra breathing time. 

According to a website called the Pond Informer, “The mating process for water scorpions typically occurs in the months of April and May. To attract a female mate, a male will perform stridulation. He will create a chirping sound that is produced when he rubs his legs against his body, similar to crickets rubbing their wings together. Once he has attracted a mate, the male water scorpion will lay diagonally across and on top of a female, and he will grab onto her thorax using his front legs. Shortly after mating has occurred, the female will deposit her eggs – she usually does this around dusk.” 

Her eggs, which are laid at or above the water’s surface in plant stems, rotting wood, or in damp spots like algae and moss near the water’s edge, have respiratory filaments that protrude from the eggs and allow them to take in oxygen https://bugguide.net/node/view/1861200/bgimage, and some sources say that the eggs can also glean oxygen from the plant stems they are inserted into.  She can lay about 30 eggs in one evening.  Newly-hatched nymphs make a dash for the water’s surface (there’s no room for breathing tubes in the egg https://bugguide.net/node/view/570259/bgimage).  

Water scorpions overwinter as adults, under the ice, equipped with a chemical defense against freezing.

Fun Fact about Water scorpions – an alarmed individual may squeak, and then it may play dead, and it may squeak if it’s scooped out of the water.  

Another Fun Fact about Water scorpions – they can sense the depth of the water they’re in by the water pressure.

Kate Redmond, The BugLady

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