The Water Stick Insect
(Ranatra linearis)

Water stick-insect
The Water Stick Insect is the largest water insect in Europe. You
might think it would "stick out" with it's 4 centimeter length (7 centimeter including the breathing
tube). But strange thing is, you easily overlook this large bug in your dipping net, where it's
taking a stiff and dead posture to mimic a little stick; and with its legs pressed against the body
you take it for a piece of old reed. So, with the debris of water plants you scooped up, you
unknowingly throw it back into the water. The specimen of the photo surprised me by its sudden
movement, otherwise I would have done the same... It turned out to be a young specimen, its
breathing tube still being short.
During its stay in a little plastic bucket, to my disappointment it seemed to float dead on
the surface one day, by then I didn't know it was just the shed skin: it had moulted. Later I saw
the bug on the bottom, still pale, with the fullgrown breathing tube. And it kept surprising me how,
every time I wanted to take a peek, it seemed to have disappeared between the water plants and only
came in sight after I poked a little bit with a small stick. It's a fascinating animal that easily
grows up in an aquarium. I raised up two from the larval state and put them back in their original
pool. For a full grown Water Stick Insect the tank must have a minimal height of 20
centimeters.
Very often you have to look hard to find the animal again, the picture on the left the animal is
better visible because lighting and background are helping. In its habitat it hangs motionless
between the Floating Pondweed stems (
Potamogeton natans), by its long mid and hind legs which
are held slanted backwards. There's the creatures favorite hiding spot, in the dim light it becomes
a stalk itself and disappears from the view of its predators and prey. Very slowly it moves up
backward until the long breathing tube touches the water surface. Almost unnoticeably the long,
slender body then rises and sinks a millimeter with each breathing in and out, because of the
difference in upward pressure. The front legs, the scythes of this Spirit of Death, are held ready
for a greedy welcome. Like the front legs of the
Water Scorpion the
feet(
tarsi) snap like a pocket knife in a groove in the thigh part (
femur) and form a
merciless trap, from which no insect leg ever gets free alive. They seem to close in an autonomic
reflex. It appeared to me that small animals are trapped when they walk over the front legs, holding
them for harmless stalks. It reminds me of a flesh-eating plant. This "silent vegetable" carnivore
has risen stealth murder, the beloved way of gathering food in pond and ditch, to a high state of
art. The reflex of the front legs harvests smaller animals, and when the eyes spot a bigger prey the
Water Stick Insect moves very slow untill the target is in reach - and with a quick draw the game is
seized.

eating May fly larva
The prey is brought to the head, the short, flexible beak is thrusted into the victim, which
is then sucked out. I don't know whether the Water Stick Insect inflict a painful nip to a human
finger. Some articles say they may, but my specimen had no intention. During its meal the bug is
often capable of catching new prey in a free front leg. Non struggling small prey is often kept on
the beak without support of one of the front legs, so the Water Stick insect sometimes carries three
victims: one in each leg and one on the proboscis. It may even catch two small animals
simultaneously with the two legs!
)¹
Some investigators think flies, that have fallen on the water surface are the stick-insect's main
source of nutrition. They are good in catching them anyway: the bug stretches the supporting legs,
so it bends slowly upwards, and with a quick haul the fly is dragged under water.
Mating is during springtime. The eggs are inserted into decomposing plants on the water surface.
They are equipped with two wires that
might have a role in air supply.

Water Stick Insect larva
THE LARVA
As with all bugs the larva already resembles the perfect insect. They have a short breathing tube
and still miss the wings. The body is spotted, this gives them camouflage between smaller water
plants. No wonder I discovered this specimen only after some days in the aquarium. They are just as
good in hunting as there parents and grow fast. After a few moults they are adult, the breathing
tube is short until the very last molt.

Water Stick Insect moulting

Larva, stealth hunting
The Water Stick Insect can be found in quiet waters between Floating Pondweed. It is able to
swim a little and has been spotted swimming in more open water. This bug is close related to the
much flatter
Water Scorpion,
Nepa cinerea. This may seem improbable,
but at a closer look the similarities are striking: the small head, the long respiration tube, the
food trapping front legs, and the life habits. Taxonomically both the genera Nepa and Ranatra are
placed in the family of Water Scorpions (
Nepidae). In America the genus Curicta
)² is found, which looks like an intermediate between the Water Stick and the Water
Scorpion. Water Stick Insects walk quicker and better than Water Scorpions when on land and some
specimen are able to fly, though this has always been doubted. There are reports however of whole
"flocks" of Water Stick Insects and an investigator found a large number stuck on a roof which had
just been tarred, the bugs probably mistook the dark shining tar for a water surface. (Many flying
water insects land on unnatural shining surfaces like dark cars and greenhouses). The flying Water
Stick could be held for a large crane fly and thus not be recognised, though at a closer look it
should be spectacular large!
)³
WEBLINKS:
1) Article about the
simultaneous catching of two prey
2) Article with
photo's about a Curicta species.
3) Photo of a winged Water Stick
Insect (American species).
back to: WATERBUGS
Page track:
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waterbugs »
Water
Stick Insect
COPYRIGHT:
All pictures on this site have been made by
G.H. Visser (Almelo,
Holland), unless otherwise mentioned. All rights remain with him. These photo's may not be used
for other then strictly private uses. In case you want to use them for purposes including third
parties, you MUST request permission, by
e-mailing the author. I
encourage especially those wanting to use the pictures for nature-expositions or other educative
targets.
© G.H. Visser 17-08-2007
rev. 09-11-2008
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