|a slender heteropterous bug, Hydrometra stagnorum, that has a greatly elongated head and is found on still or sluggish water where it preys on water fleas, mosquito larvae, etc|
any insect of the family Hydrometridae (order Heteroptera), so named because of its slow, deliberate manner of moving as it walks along the surface of a pond or crawls among shore vegetation. Marsh treaders, worldwide in distribution, are usually found among the cattails in marshy ponds containing algae. More than 100 species of the insect have been described.
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