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Water strider, Gerris spec.
Water strider click to ENLARGE
THE WATER STRIDER IS THE WATER BUG EVERYBODY RECOGNISES. The name POND SKATER is often given to the larger species. When you sit down on the border of a pond or stream on a fine spring day, you are almost certain to see them. From april to far in october they can be found everywhere where the smallest puddle of water is: on ditches, wet meadows, margins of lakes and the smallest garden ponds. On your garden pond they stand in loose groups, sometimes they seem to dream in the sun and move only if a dull breeze tries to blow them from their spots, but often running and sliding like real skaters. On streams they are constantly rowing upstream to stay put. Where the current is too strong, they move to more quiet corners. On quick brooks, especially in the woods, their place is taken over by the Water crickets. Water striders cannot live on high waves either. That's why they never go far from the border, though the larger Pond skaters dare to go on more open water. There are days with a lot of activity: they sprint towards each other, wrestle a short time, turn on their back or even jump up from the water surface to ten centimeters in the air! They are also able to run very fast by means of a series of jumps. Let's transform the speed of these insects to the scale of a human being: in one second a 1.5 cm sized Water strider races a meter with ease. For a 1.5 m sized human that means 100 meter per second, or: 360 kilometers per hour - and that while running on water! The propulsion is delivered by the middle legs, which are spread out like oars that are not in the water but just slide over the surface. The hydro mechanics of this feature are very complicated and have been a source for many researches, see the links on the bottom of this page. The last legs are not used for the propulsion, they are supports and oars. The front legs are mostly held folded in and are used for grabbing the prey.

Water striders with fly
click to enlarge
Water striders are the micro-hyena's of the water surface. There they rule, while countless numbers of little insects that fall on that same surface, are doomed. When the skating hunters with their bulgy eyes spot the helpless struggling victims, they attack immediately and suck the life out of their prey. Sometimes like a pack of wolves, as on the picture on the right, where eight Water striders are feasting on a fly.
Gerris species, Water strider, head and snout
click to enlarge
But on most occasions they keep it for themselves, sledding the prey in front of them, away from hungry fellow striders. And the competition is heavy: beside Water strider colleagues there are Whirligig beetles and Water boatsmen who search their prey on the surface. Water striders have a real bughead as can be seen on the left: narrow, with bulgy eyes, long antennae and the beak (proboscis), that is typical for bugs and consists of the the mouth parts which are reformed to a long, piercing sucking tube. The razor sharp inner mouth parts are elongated in the body, so the point of the beak can protrude quite far. Bigger prey is approached carefully, the Water strider nips it with his beak and if there is too much struggling than he jumps to a fake respectful distance to wait a while. Sometimes a fish or newt may snatch their banquet in one gobble... The Water strider itself must take care not to be eaten by a fish. When attacked it runs with high jumps very fast a astonishing distance and (mostly) escapes in that way.

Gerris species, Water striders with dents in the Water surface
It keeps us amazed how insects and spiders may walk on the water, but the Water strider is the champion with its swift manoeuvres and high jumps. The surface is clearly dented in like a tough film, but doesn't break. It's a classical school example of the surface tension of water.
Gerris species, Water striders with dents
Of course many research has been done to clear this secret of the Water strider. Much can be found on the Web. The body and legs are covered with a water repellent fur coat. The hairs itself have a micro structure which keeps air enclosed. Moreover they are covered with a tiny layer of wax. This makes the contact angle for water very high, which means they are very water repellent. For more about the contact angle and surface tension read the page about the water surface. Click the links on the bottom of this page to see other web sites about this subject. Water striders may not sink into the water, they are not able to dive like the Water cricket. That's why polish their hair coating continuously to keep the water resistance at the max. And that's also why the water on which they live, may not be polluted with substances that lower the water resistance, like dish washers detergents. Garden ponds qualify perfectly as a living habitat and there you can observe these amusing and interesting with ease. They can be held at the water of a small aquarium for a few days, just mind that the animals have a tendency to jump out, so don't fill the tank too high or use a glass cover. If they are to be transported, it should not be done in a dashing jar of water, that will drown them very quick. Use a box or a ventilated plastic box with some wet water plants or moss. This is best for most water insects by the way - they have no gills.

Gerris (?) species, larger species Water strider
click a picture to enlarge
Two other pictures of Water striders. On the left a larger species, maybe Gerris najas. On the right one a smaller species, Gerris lacustris? Mark the different length of the wings. That isn't a difference between the species, the individuals of one and the same species may also have different wing lengths. This fact is common with many bug species. According to the length of the ptera (wing) there are aptere specimen without wings, microptere with very small, brachyptere with short and macroptere with fully developed wings.


Next page: the reproduction of the Water strider.


WEB LINKS:
Micro-photos of the hairs
Robostrider, an artificial Water strider and on the hydro mechanics (Dutch) .
Another robot Water strider.
Nice demo contact angle.
Sharp picture of a Water strider.




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COPYRIGHT:
All pictures on this site were made by Gerard Visser (Almelo, Netherlands), unless stated otherwise. All rights remain with him. These pictures may not be used for purposes any other than private viewing or printing. Do NOT hardlink to these pictures or place them on other websites without the author's approval. Should you need them for purposes which include third parties, you must ask the author permission by e-mail. People, who want to use this pictures for exhibitions or publications or educative material are much encouraged to do so, after approval as mentioned and giving the normal credits.
© G.H. Visser 29-01-2007
rev. 27-10-2007


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