Water measurers have elongated heads (longer than the thorax) with eyes set far back. This one is about 6 mm long (excluding antennae and legs), but they may reach twice that length. They are dark in color, often brown or blue-gray.

Water measurers are usually found on the surface of still water held up by surface tension or creeping on vegetation nearby. They have a sharp beak that allows them to spear prey through the water surface, and they then suck out the inside of the prey. Mosquito larvae seem to be a favorite prey.

There are 9 Hyrometra species in North America.

Although these insects look somewhat similar to water scorpions, they are much smaller and are found on the water surface rather than below it.