Wikijunior:Bugs/Pondskater/Water Strider

What does it look like?

Water striders are among the most recognizable aquatic insects. Most species have long, slender bodies covered with thick, velvety, water-repelling hairs. Some species have shorter and rounder bodies. They have large prominent eyes and are usually dark brown to black in color. Some have stripes on their bodies. Others have yellow on top of the head. Many water striders are very small (6/100 inch) and others are relatively long (1-1/2 inches). Females are generally larger than males.

Water striders have two short forelegs, two long middle legs and two long hind legs. The middle and hind legs are used for locomotion. Each leg is covered with thousands of microscopic, water-repelling hairs to keep them dry. Wet legs would break through the surface of the water, causing the water strider to sink. The hairs have grooves that trap air, increasing buoyancy and water resistance. Scientists use the term “superhydrophobic” to describe how the hairs repel water.

There is an air cushion between water striders feet and the water surface. The purpose of this cushion is to create stability and maintain balance even in rainstorms. There are claws above the foot instead of at the end, so the water surface does not break.

Where does it live?

Scientists believe there are about 500 water strider species worldwide. They estimate 45 to 60 species live in North America. Aquarius remigis is the scientific name for one species commonly found in eastern North America. Water striders spend their entire lives on the water’s surface. They can be seen on lakes, ponds and calm parts of rivers and streams.

Five water strider species roam the ocean. These insects, known as sea skaters, are the only true marine insect. Their scientific name is Halobates. They have adapted to life on the open seas in warm areas of the Atlantic, Pacific, and Indian oceans. Often, they are seen on tide pools or in debris that has washed ashore.

What does it eat?

Water striders are generally predators. They survive by capturing and feeding on other creatures. They eat newly hatched tadpoles and mosquito larvae that float to the surface. They often eat dead insects. Sea skaters depend on finding floating fish eggs and other sources of protein.

Water striders eat land-dwelling insects that drop into the water. When insects drop they are caught on the water’s surface. As they struggle, they send “communication ripples” over the surface. Water striders detect these ripples through sensory receptors on the tips of their legs. They dart quickly to grab the insect prey with their strong front legs.

Because they are “true bugs,” water striders are able to swing their beak forward from its resting position on the underside of the body. The beak is used to pierce the prey and inject it with digestive juices. The juices dissolve and liquefy internal organs allowing the water strider to suck out nourishment.

How does it defend itself?

Water striders are eaten by birds, fish, frogs,and aquatic insects. They are especially vulnerable when mating. One defense against predators is camouflage. Resting on floating leaves and vegetation lets water striders blend into their surroundings. Their large prominent eyes help them avoid predators.

What stages of metamorphosis does it go through?

Water striders mate on the water’s surface. In some species, the males are territorial and defend small circles while waiting for females to drift by. Females are sometimes lured by vibrations made by a male tapping its legs on the water surface.

Females lay rows of eggs on submerged plants, rocks, logs or floating objects. Sometimes eggs are inserted into a plant stem.

Water striders develop through simple metamorphosis. The immature stages are called nymphs. They resemble adults but are smaller in size. Their wings are not as fully developed as adult wings. Nymphs live below the water surface where they molt five times before becoming adults. After hatching they must swim upward and break the surface tension to get to the top of the water. They begin to skate as soon as they are afloat. One or two generations of water striders mature each year.

For the sea skaters, finding places to lay eggs is more difficult. They use any floating object, including feathers, seaweed, and live seabirds.

What special behavior does it exhibit?

Because they have the unique ability to move about on the surface, water striders are known as “skaters,” “scooters,” or “wherrymen.” Sometimes they are called “Jesus Bugs” because they appear to “walk” on water.

Long middle and hind legs spread the weight evenly over the water surface. The “surface tension” of calm, smooth water keeps them afloat. Surface tension is the tendency of water molecules to cling to each other. It creates a thin film that water striders can float on without breaking through.

Water striders move in two different ways—skating in a slow, graceful glide or darting in a quick, spurting motion. Skating is done when moving upstream against a current or getting to food and other striders. Gliding is done by “rowing” with the middle legs. Feet press down on the water’s surface creating little dimples around them. Like the blades of an oar, the dimples generate hidden underwater currents that move the insect forward. Hind legs act as rudders and brakes. Front legs are free to snare prey.

Darting is done whenever quick movement is needed—to escape danger, pursue prey, or grab females. Darting uses both middle and back legs for propulsion. Water striders can dart a distance of 100 body lengths per second. That would be 400 miles per hour for a six foot tall person. SCIENTIFIC CLASSIFICATION

KINGDOM - Animal

PHYLUM - Arthropod

CLASS - Insect

ORDER - Hemiptera

FAMILY - Gerridae

GENUS - Gerris

SPECIES - Gerris remigis

How does this bug affect people?

Water Striders are considered beneficial because they prey on other insects including mosquito larvae. They are medically harmless and are not known to bite. They leave a minor sting that goes away without treatment but it leaves a small red mark for several hours. They do not require management.

References

AgriLIFE Extension Texas A & M [1]

Britt, R. R. (2004). Walking on water: Insect’s secret revealed. Live Science. [2]

Carpenter, A. (2005). A walk on the wet side. Wisconsin Natural Resources Magazine. [3]

O’Toole, C. (Ed.). (2002). Firefly encyclopedia of insects and spiders. Richmond Hill, Ontario: Firefly Books Ltd.

Handwerk, B. (2004). Hairy legs help bugs walk on water. National Geographic News. [4]

Leahy, C. (1987). Peterson first guide to insects of North America. Boston, MA: Houghton Mifflin Company.

Marshall, S. A. (2006). Insects their natural history and diversity. Richmond Hill, Ontario: Firefly Books Ltd.

McGavin,G. C. (2000). Insects spiders and other terrestrial arthropods. New York, NY: Dorling Kindersley, Inc.

Milne, L. & Milne, M. (1980). National Audubon Society, Field guide to North American insects and spiders. New York, NY: Alfred A. Knopf, Inc.

Owen, J. (2003). Robot helps show that water striders “row” on H₂0. National Geographic News. [5]

Raven, P. H. & Johnson, G. B. (1999). Biology (5th ed.). Boston, MA: WCB/McGraw-Hill.

Turpin, T. (1993). Water striders thrive on tension. On Six Legs. [6]