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This Is Why Water Striders Make Terrible Lifeguards | Deep Look

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Channel: Deep Look
Categories: Biology   |   Environmental   |   Science  
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They may look serene as they glide across the surface of a stream, but don't be fooled by water striders. They're actually searching for prey for whom a babbling brook quickly becomes an inescapable death trap.

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DEEP LOOK is a ultra-HD (4K) short video series created by KQED San Francisco and presented by PBS Digital Studios. See the unseen at the very edge of our visible world. Get a new perspective on our place in the universe. Explore big scientific mysteries by going incredibly small.


With the drought officially over and the summer heat upon us, people all across California are heading outdoors. For many, that means a day on the river or relaxing by the lake. The wet winter means there’s plenty of habitat for one of nature’s most curious creatures.

Water striders, also called pond skaters, seem to defy gravity. You’ve probably seen them flitting across the water’s surface, dodging ripples as they patrol streams and quiet backwater eddies.

Scientists like David Hu at Georgia Institute of Technology study how water striders move and how they make their living as predators lurking on the water’s surface. It’s an amazing combination of biology and physics best understood by looking up close. Very close.

--- What are water striders?
The common water strider (Gerris lacustris) is an insect typically found in slowly moving freshwater streams and ponds. They are able to move on the water's surface without sinking. They are easy to spot because they create circular waves on the surface of the water.

--- How do water striders walk on water?
Water tends to stick to itself (cohesion), especially at the surface where it meets the air (surface tension). Water striders don’t weigh very much and they spread their weight out with their long legs. Striders are also covered in microscopic hairs called micro-setae that repel water. Instead of sinking into the water, their legs push down and create dimples.

--- What do water striders eat?
Water striders are predators and scavengers. They use their ability to walk on water to their advantage, primarily eating other insects that fall into the water at get trapped by the surface tension. A water strider uses its tube-shaped proboscis to penetrate their prey’s exoskeleton, inject digestive enzymes and suck out the prey’s pre-digested innards.

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