MARSH TREADER

Water measurers are long, slender insects that are up to 15 mm long. They have long stilt-like legs that move in a slow, deliberate way while stepping across the water among thick, plant cover near the shore of the pond. They walk so carefully that it seems they are measuring each step. That is why they are called 'water measurers'. They hold their bodies well above the water. The two back pair of legs point backward and the front legs point forward. The legs of the water measurer are easily broken off.

Water Measurers are dark grey in color. They look like water scorpions without the long breathing tube. They have long slender heads with bulging eyes a little behind the middle point of their heads. Their heads are as long as the thorax or middle part of the body. The long antennae look elbowed or bent. They have long beaks with which to spear their prey and suck out body fluids. Unlike both water striders and water scorpions, water measurers do not grasp the prey with their front legs.         
Like the water treader, water measurers walk on the water's surface with all six legs. The places, where the legs join the body are spaced further apart along the long thorax than is the case for the water scorpion or water strider.
The water measurer feeds on mosquito larvae and pupae, other water insects and small crustaceans. It is eaten by larger insects, birds, amphibians and reptiles.
The eggs of the water measurer are laid in the stems of cattail sprouts, grasses and water plants. The eggs are brown, spindle-shaped and covered with a horny coating. They are laid one at a time from April to June.   After 17 days, the nymphs hatch. They look like shorter versions of the adults. The nymphs molt five times, gradually changing into adults.

Description: Thin, fragile-looking insects with long threadlike legs and antennae; their body length reaching about 2/5 inch. The head is unusually long in relation to the body, with the eyes a little behind the midpoint. Although some adults have wings and are capable of flight, most are wingless. The general body color is light brown, rendering these insects inconspicuous in their usual habitat.

Similar Species: In the net they somewhat resemble water scorpion nymphs but lack the raptorial front legs and long abdominal air tube. The elongate head of the marsh treader also differs from the relatively short head of the water scorpion.

Habitat: Marsh treaders are widespread in the U.S., with Hydrometra martini being by far the commonest species. They occur on floating vegetation such as mats of decaying reeds or cattail stems, filamentous algae, or duckweed, or on leaves of water lilies in marshes, ponds, or lakes. They also occur along the margins of ponds or slow-moving streams. H. martini is found at both the butterfly garden pool and at Silver Spring pond.

Life Cycle: H. martini adults overwinter in debris on land. Egg laying begins in early spring. The spindle-shaped eggs are deposited vertically on vegetation or other objects just above the water surface. Eggs take about 2 weeks, on average, to hatch. The 5 nymphal stages, which resemble the adults, are completed in 2 to 3 weeks, depending on temperature. Three or more generations may occur per year.

Movement: While they can run across the water surface, they usually walk slowly over surface vegetation. Although they may rarely do so, they are capable of swimming underwater, as nymphs have been observed to do.

Breathing: Marsh treaders breathe air through special openings in the body wall, called spiracles, that open into the trachea, or air tubes, that run throughout their body.

Prey/Predators: They feed on all kinds of small aquatic organisms that they spear at and just below the water surface. They are preyed on by various aquatic species, like backswimmers, newts, and small fish, that can capture insects on the water surface.

Behavior: Their habit of very slowly and deliberately walking over surface vegetation or across the surface of small pools is distinctive

 

   Fact Sheet                 Water Measurer