AT A GLANCE
- Common Name: Water Stick Insect
- Scientific Name: Ranatra linearis
- Category: Invertebrates
- Subcategory: Insects
- Range: Widespread across the Palearctic realm, throughout Europe, North Africa, the Middle East, and temperate Asia to China and Siberia
- Habitat Type: Quiet freshwater ponds, oxbow lakes, weed-choked drainage ditches, flooded gravel pits, and sluggish river margins with abundant submerged aquatic plants
- IUCN Red List Status: Not Evaluated (widely distributed and common)
- Lifespan: 1 to 2 years (adults overwinter in deep water mud)
- Diet: Carnivorous/Aquatic predator (water fleas, mosquito larvae, tadpoles, tiny fish fry, mayfly nymphs, and small backswimmers)
- Average Size/Weight: Body length 30 to 40 mm (excluding breathing tube); breathing siphon adds another 25 to 30 mm; total length up to 70 mm
- Key Defining Feature: Impossibly slender, needle-like aquatic true bug resembling a sunken twig, possessing mantis-like raptorial front claws and an extraordinarily long rear snorkel breathing siphon
Overview
The Water Stick Insect (Ranatra linearis) is one of the most bizarre and cunning predatory insects inhabiting European freshwaters. Despite its common name, it is not a terrestrial stick insect (order Phasmatodea), but rather an aquatic true bug in the water scorpion family Nepidae (order Hemiptera). Looking like a decaying brown pine needle or submerged twig, it clings motionless among water weeds, breathing atmospheric air through a long, tail-like snorkel siphon while waiting to ambush passing tadpoles with raptorial front legs identical to a praying mantis.
Biology and Physical Characteristics
Ranatra linearis has an extraordinarily elongated, cylindrical, stick-like body colored a dull yellowish-brown, greyish-ochre, or muddy olive that mimics dead reeds. Its front legs are heavily modified into grasping, raptorial pincers with sharp, folded segments that snap shut like a pocket knife. The middle and hind legs are very long, thin, and spindly, used for crawling slowly through dense submerged vegetation rather than fast swimming. Extending from the tip of the abdomen is a remarkable breathing apparatus: two long, grooved, interlocking filaments that form a hollow, air-conducting tube (siphon) that can reach up to 30 mm in length. Beneath its brown wing cases lie functional, translucent wings that allow adults to fly between ponds on warm summer nights.
Behavior and Ecology
Living among submerged hornwort, water-milfoil, and reed stems, the Water Stick Insect hangs head-downwards, extending the tip of its rear breathing siphon up through the surface film to draw oxygen into its tracheal system like a deep-sea diver’s snorkel. Because it moves so slowly and deliberately, it is virtually invisible to both fish and prey. When an unsuspecting mosquito larva, water flea, or small tadpole swims within reach, the insect’s raptorial front legs snap forward with lightning speed, pinning the victim tightly against its thorax. It then pierces the prey with its sharp, pointed rostrum (beak), injecting paralyzing digestive saliva before sucking out the liquefied body contents.
Conservation and Human Impact
The Water Stick Insect has not been evaluated by the IUCN, but is widely distributed and common across lowland Europe and Asia. Because it relies on healthy submerged aquatic macrophyte beds and clean water, populations can decline when farm ponds are filled in, heavily eutrophied with fertilizers, or cleared of all native vegetation.
Interesting Factoid
The Water Stick Insect is an underwater praying mantis with its own built-in snorkel; it hangs upside down in pond weeds and breathes atmospheric air through a long hollow tube sticking out of its rear end like a periscope.