Water Stick Insect

The water stick insect is a true bug, not a true stick insect, and its resemblance to a floating twig is a remarkable case of convergent camouflage rather than close relationship to the walking sticks (Phasmatodea). It belongs to the family Nepidae, the water scorpions, and shares that family's ambush hunting style and needle-like breathing tube, but has a slimmer, more elongated body than its stouter relative the water scorpion.

It is an entirely aquatic predator throughout its nymph and adult life, spending most of its time clinging motionless to submerged plant stems with only the tip of its breathing tube reaching the surface film. This sit-and-wait strategy, combined with its stick-like shape, makes it almost invisible among pondweed until prey blunders within reach.

As a mid-level predator, the water stick insect helps regulate populations of small invertebrates in ponds and ditches, and it is in turn eaten by fish, larger aquatic insects, and wading birds.

• Extremely slender, elongated body resembling a floating twig, grey-brown to olive in colour
• Long, thin front legs modified into raptorial grasping tools, held folded like a praying mantis
• Thinner, thread-like middle and hind legs used for clinging to plants
• Long, thin paired breathing tube (siphon) at the tip of the abdomen, used like a snorkel
• Wings present but rarely used for flight; body shape is the main identification clue
• Distinguished from the water scorpion (Nepa cinerea) by its much narrower, more elongated body and proportionally longer legs

Water stick insects favour still or gently flowing water with abundant submerged and emergent vegetation, including ponds, canals, ditches, and the quieter margins of lakes. They are found across much of Europe and temperate Asia, usually in shallow water close to plant stems where they can anchor themselves and extend their breathing tube to the surface. They are most easily encountered from spring through autumn, becoming less active and often burrowing into bottom debris during colder months.

This is a patient ambush predator that remains almost perfectly still, gripping a submerged stem while extending its breathing tube to the surface for air. When a small invertebrate such as a mosquito larva, water flea, or other aquatic insect comes within range, the water stick insect strikes with its spined raptorial front legs and pierces the prey with its short, sturdy rostrum to feed on body fluids. It is a poor swimmer and instead crawls slowly among vegetation, relying on camouflage and stillness rather than speed to both catch prey and avoid predators. Adults can fly and occasionally do so to disperse to new water bodies, particularly at night.

Females insert eggs into plant tissue or floating debris just below the waterline, each egg bearing two thread-like filaments that project into the water and are thought to aid gas exchange. Nymphs hatch resembling miniature, wingless adults and pass through several instars underwater, developing incomplete (simple) metamorphosis with no pupal stage. Growth continues through the warmer months, with adults typically present from spring to autumn in temperate regions; in many populations there is one generation per year, with adults or late-stage nymphs overwintering in sheltered mud or debris at the bottom of the water body.