Support Of A Different Sort

This week's theme for PhotoHunt is 'support'. Luckily I could think of several potential subjects, but one in particular kept coming back to me. I've always been amazed by the ability of some insects and spiders to walk on water. This recent photo of a water spider came to mind. Actually I think it is more accurately called a fishing spider, but the photo is not detailed enough for me to make a good determination. If I'm not mistaken the true water spiders actually live in the water and can swim underwater. Regardless, this spider uses the surface tension of water to 'support' itself on the water. It's legs are 'hydrophobic' meaning they resist being wetted by water. It's somewhat like wax on a car making the water bead into droplets.

I don't normally go looking for spiders to take photo's of, but sometimes they are just too obvious to pass up. I do watch them from time to time as they scurry across the water. They are amazingly fast. Some insects/spiders can move across the water at a rate of up to 30 body lengths per second. That's maybe 4 inches per second. Perhaps that doesn't sound that fast, but compared to the fastest sprinters who can run about 5 body lengths per second it rates pretty good.

A few days ago I witnessed an unusual maneuver by one of the large spiders. He was easing along when all of a sudden - sproing - he made a vertical leap straight up in the air as though he had been shocked. When he hit the water again he was off in a flash. Presumably this is an evasive action when the spider is startled or senses a predator such as a trout or bass approaching from underneath.

There are not a lot of these spiders at the pond, at least not the size of these. Most often they are not actually on the water, but resting on twigs, grass, or leaves at the edge of the pond. Evidently it takes a lot of energy to walk on the water as the spider has to remain tensed to distribute its weight effectively.

Of course, where you find big spiders you usually find baby spiders. (I presume these are spiders but they may be some type of water insect. It's hard to tell in the photo.)

Oddly most of the readily visible spiders are found along the northern bank of the pond. I'm presume that has something to do with the type of vegetation in or near the water and the amount of sun the area gets throughout the year. Also, more of the floating debris such as leaves, pollen, and such tends to wind up on the northern bank.

When you think about it, walking on water is a pretty neat trick. It's not just the issue of remaining out of the water, but also how do you move. Movement is all about action and reaction. Most walking creatures require friction to move themselves from one place to another. Your foot is held to the surface you are on by friction and your muscles propel you forward. Imagine standing on slick ice and trying to start running and you can see what I mean.

Well, since the spiders legs are hydrophobic and just barely actually 'touch' the water, how do they move without the tip of the leg slipping? The way I understand it the water spider does not exactly use that same type of action that we do. It uses an action similar to rowing. It actually pushes the slight dimple its legs produce in the surface tension of the water backwards which moves its body forward like an oar pushes the water back and the boat forward. For faster movement, such as moving to escape a potential predator, the legs actually penetrate the surface tension slightly, but the spider is so light its forward motion keeps its legs from sinking too deeply.

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For you PhotoHunt visitors I have a little post script. I'm sure many of you may have experienced this same type thing frequently. Last week's theme was 'pointed'. Just after I had made my theme photo post I happened to take a photo that would have been great for pointed. The photo is not of the best quality as the subject was about 10 feet up in a tree and it was getting late in the day, but I'm sure you will appreciate the 'pointed' aspect it displays. If anyone has an idea what this is I would like to know.

PhotoHunt
Weekly Theme - Support