Water Measurer
Hydrometra stagnorum
The Water Measurer is a very slender, rod-shaped bug with a characteristically elongated head. It lives primarily on the surface of standing or slow-moving water and among riparian vegetation. Unlike the agile pond skaters, it moves slowly and in a stilt-like manner. The species is usually wingless, but fully winged individuals occur occasionally.
Details
Identification
Extremely slender body, head longer than the thorax, four-segmented antennae, usually dark brown to black in color.
Social behavior
Mostly solitary lifestyle, but often forms loose aggregations at favorable shore locations without social interaction.
Diet
Predatory diet consisting of small invertebrates such as mosquito larvae, water fleas, and terrestrial insects trapped on the surface film.
Hunting strategy
Slow patrolling or ambush hunting; the prey is fixed with the front legs and sucked out with the piercing rostrum.
Spawning substrate
Eggs are attached individually to plant parts or stones just above the water level.
Overwintering
Overwinters as an adult on land in leaf litter or under moss near the water.
Ecology
Ecological role
Acts as a predator in the neuston and contributes to the control of mosquito populations; serves as food for fish.
Natural predators
Small fish, backswimmers, larger pond skaters, and insectivorous birds.
Competitor species
Other pond skaters (Gerridae) and riffle bugs (Veliidae).
Ecosystem service
Biological pest control by feeding on mosquito larvae.
Threats
Loss of near-natural shore structures, riverbank reinforcement, and chemical pollution of water bodies.
Scientific profile
Profile
Distinguishing features
Extremely slender, rod-shaped body. The head is greatly elongated and significantly longer than the pronotum; the eyes are located approximately in the middle of the sides of the head. Hydrometra stagnorum is usually apterous (wingless) or brachypterous (short-winged), while macropterous (long-winged) individuals are rare. Compared to H. gracilenta, it is larger and the distance from the eye to the tip of the head is about twice the distance from the eye to the base of the head.
Role in food web
Secondary consumer; regulates populations of small surface organisms and serves as prey for larger aquatic and semi-aquatic predators.
Protection & threats
Main threats
Loss of natural shore structures, removal of riparian vegetation, heavy wave action from shipping, and drainage of small water bodies.
Population trend
Stable; the species is widespread and common in Central Europe.
Conservation measures
Preservation and restoration of near-natural riparian zones with reed and sedge beds. Avoidance of intensive mowing of shore vegetation.