Water Strider
Walking on Water: The Water Strider
Georges River Land Trust — Living River Species Series
Introduction
Every calm pool and slow backwater of the St. George River hosts a community that lives in a place most animals cannot access: the surface of the water itself. Water striders (Family Gerridae) skate across the film between air and water with effortless speed, leaving only tiny dimples where their legs touch — and not breaking through. Children notice them immediately and want to know how. The answer turns out to involve physics, microscopic hairs, and a sensory system so finely tuned that the strider can detect a struggling insect from across a pool through vibrations alone. The water strider is a small animal with an extraordinary relationship with its environment, and the calm pools of the St. George watershed are better, more ecologically complete places for having them.
Natural History
Water striders are true bugs — members of the Order Hemiptera, the same group as stink bugs and assassin bugs — equipped with the piercing, sucking mouthpart called a rostrum that all true bugs share. Several species inhabit Maine's freshwaters, with members of the genus Gerris being the most common on streams and ponds.
The secret to walking on water is not magic but microscopic engineering. Each of the strider's six legs is covered in thousands of tiny, water-repellent hairs — called hydrofuge setae — that trap a layer of air against the leg surface. This prevents the leg from breaking through the water's surface tension, and the broad spread of the middle and hind legs distributes the insect's weight across a large enough area that the surface film holds. The result is four small dimples in the surface where the legs rest, each dimple casting an oval shadow on the streambed below — often larger than the insect itself, and sometimes the first thing a watching trout or heron notices.
Water striders are predators, feeding on insects that fall onto or become trapped in the water surface — ants, small flies, beetles, moths, and any other terrestrial insect that makes the mistake of landing on or being blown into the stream. The strider detects its prey not by sight but by surface vibrations — the ripples a struggling insect creates spread outward like concentric rings, and the strider's legs sense these waves and orient toward their source with speed and precision. Once the prey is located, the rostrum is driven in and digestive saliva injected, liquefying the soft internal tissues, which the strider then draws out. It is an efficient and entirely successful hunting strategy for an insect that occupies one of the most nutrient-rich surfaces in the watershed: the exact spot where terrestrial insects fall in from overhanging vegetation and aquatic insects emerge to become adults.
Identification Tips
Water striders are easy to identify by posture and behavior alone: a slender, dark body held up on four long, widely splayed legs that rest on the surface film, each leg producing a small dimpled shadow on the streambed below, with a much shorter front pair used for grabbing prey. They skate and dart rather than swim, never breaking the surface tension. This sets them apart from whirligig beetles, which are compact, shiny, and spin in tight loops while partly submerged. Water striders cluster in the calmest water available — quiet pools, eddies behind rocks, and sheltered pond margins — and are most visible on still, sunny days when their shadows stand out clearly on the bottom.
Role in the St. George River Watershed
Water striders occupy a niche that no other organism in the watershed fills in quite the same way — the interface between air and water — and their ecological role reflects that position.
As predators of terrestrial insects that fall onto the stream surface, they capture energy that would otherwise drift downstream unused or sink to the streambed. Ants knocked from streamside alders and willows, small moths and midges, beetles and crane flies — all become food at the surface film. In doing so, water striders transfer nutrients from the riparian forest into the aquatic food chain.
They also scavenge spent aquatic insects — the exhausted adults of mayflies, caddisflies, and stoneflies that fall back onto the water after mating, too depleted to escape. The surface of a calm pool on a summer evening after a mayfly hatch is, from the water strider's perspective, a feast.
Brook trout and smallmouth bass eat water striders, striking from below — though the strider's ability to detect the pressure wave of an approaching fish through the surface gives it a fraction-of-a-second warning. Frogs and toads take them from the water's edge, as do great blue herons and occasionally belted kingfishers. Tree swallows occasionally snatch them from the surface in flight.
Their preference for calm, slow-moving water — shaded pools, eddies behind rocks, pond margins sheltered by emergent vegetation — means they are closely associated with the cattails, water lilies, and aquatic sedge beds of the watershed's quieter reaches. These plant communities create the still-water conditions the strider requires, and the overhanging vegetation above them delivers the terrestrial insect prey the strider depends on.
Water striders are year-round residents in adult form, one of the few aquatic insects that overwinters above water rather than as eggs or nymphs. In autumn they leave the water and shelter under leaf litter, bark, and streamside logs, emerging again in early spring to be among the first insects visible on the water's surface — sometimes while ice still lingers on shaded edges.
Seasonal Notes
Water striders are visible on the water surface from April through October, appearing some years while ice still covers parts of shaded pools. Population numbers build through May and June as individuals mate and lay eggs along the edges of aquatic plants. Summer brings the highest densities, with striders concentrated in calm pools and lake margins. On warm autumn days they remain active well into October before retreating to overwinter under streamside debris. Early spring mornings — when the water is still and cold and few other insects are active — offer some of the clearest views of their skating behavior.
Fun Fact
Water striders communicate with each other using deliberate ripple signals — not just detecting ripples passively, but generating them intentionally. Males produce species-specific ripple patterns by rapidly vibrating their legs against the surface, sending courtship signals to females and territorial warnings to rival males. Researchers studying these signals found they are structured enough to carry distinct information: a male's courtship ripple and his rival-warning ripple are measurably different waveforms, and females respond selectively to each. The water strider is, in effect, conducting a conversation on the surface of the stream in a language made entirely of waves.
Want to Learn More?
- Bug Guide — Gerridae — Photographic identification guide to North American water strider species.
- Maine DEP — Surface Water Ecology — Maine's freshwater monitoring programs and the ecological communities they track.
- iNaturalist — Water Striders — Regional sightings and community photographs from New England naturalists.
- Xerces Society — Aquatic Invertebrates — Conservation context for aquatic insects and the freshwater habitats that support them.
The Living River blog series is published by St. George Consulting in support of the Georges River Land Trust and the Maine Council of Trout Unlimited. To explore the important work these organizations are doing to conserve and restore Maine's landscapes, visit georgesriver.org and tumaine.org.