This past week we began working with a graduate student named Jae Hak on water striders. The goal of this research is essentially to understand water strider jump locomotion. However, we will also examine the effects of added weight on jump behavior and mechanics as well as the probability of mating female jumping. The core of the research I examined during the past school semester. This involved understanding the hydrophobic properties of the water strider's bodies/legs (they have air pockets in the hairs on legs to keep them above the water surface), and the basic mechanisms of their jump i.e. legs row across the water surface, propel downward - treating the water surface as a trampoline - and launching their bodies off the water in order to escape predation from below the water.
We collected the water striders from ponds, and streams nearby the SNU campus by peering intently at the water. Using a net to scoop and capture. I actually ended up taking a nice, little, cold swim in one of the pools of water during our second water strider collecting expadition. We were hiking down a low grade waterfall, and I decided that a particularly slippery and wet rock was a great place to stand. Needless to say, my feet slid out from underneath me, and I plunged feet-first into chilly water. I would like to note here that neither Christina NOR Jae Hak made any attempt to save me, just watching casually as I slid further into the pond. With every movement I made to get out of the water, my feet slipped further into the coating of decomposing leaves beneath the water surface. Now, I eventually did get out - without any help - but the lower half of my body was thoroughly saturated with H2O… Unfortunately, I don't have any picture evidence that this occurred. Only the memories of Christina and Jae Hak… Which is probably a good thing…
After collecting the water striders, we had to mark their backs with three color coded spots of paint. In order to begin this process we had to first identify the sex of the each water strider. Generally the females have more protected genital parts, their abdomens continue further down than in a male water strider. Also, the female water striders are typically much larger than the males. After sexing the marking began. The females started with a dot of the blue color (signifies the number 3), and each addition was consecutive. The male water striders began with the color red (1). Due to the fact that we will be examining the effects of added weight, we thought it necessary to see if the added paint spots increased the weight of the water strider. In order to test this theory, we weighted each water strider before and after the addition of paint. Surprisingly, every water strider tested weighed less after the paint was added.
Christina and I spent much of the week determining the best placement, amount etc. for the light and camera positions in order to best record the water strider jumps. As seen in the picture, the placement includes two (eye burning) bright lamps, directly opposite two cameras. In the middle is a clear box filled with water in which the water strider is placed. There will eventually be a third camera collecting bird's-eye video, however at this point Christina and I still had to learn the program necessary to analyze the 3D data (MaxTRAQ). We practiced filming the water striders in 2D, getting used to the equipment. The camera on the left is the "master" camera, and the camera on the right is the "slave," meaning the left camera controls the actions of the camera on the right. Recording the water striders proved to be very technical. In order to facilitate a water strider jump, we used a bent wire to lightly tap the water strider's abdomen from below the water. In theory, this would cause the water strider to jump gracefully from the water surface. However, the water striders were often unresponsive to the wire, or were overactive - constantly jumping and throwing themselves at the walls of the container - and it proved difficult to record a clean, successful jump in which the water striders legs do not puncture the surface of the water. One important thing to understand about water striders is that when they get fully wet, they can no longer remain at the surface of the water. If they cannot find a hard surface to clean the water from their hairs, they will drown. Touching the water striders also effects their hydrophobicity. The more you touch a water strider, the less effectively it will remain on the surface of the water. Although the process can be long, watching a water strider jump in close proximity after spending an entire semester reading papers that described the process was highly interesting! It was amazing to see the way their legs simply rowed across the water surface, jumping off it like a trampoline, and sometimes jumping completely out of the box!
We also learned how to feed the water striders, and Jae Hak keeps a store of frozen crickets in the freezer solely for this purpose! The crickets must first be hacked out of the frozen containers and thawed in lukewarm water. After thawing we have to carefully place each bug so it floats on the surface of the water. Any bug that sinks will not be eaten, seeing as water striders do not have the ability to dive. Feeding the water striders is not a difficult process, but cleaning out the old, eaten bugs smells a lot worse than one would think…
This picture illustrates the process of thawing out the crickets.
This picture illustrates the process of thawing out the crickets.
This week Christina and I are beginning to learn the software necessary to analyze 3D data, this is proving to be a long and complex process full of many online tutorials and uses of the search bar… I super glued several fingers together today… (just a bit of preview for next week's research summary). See ya'll next week!