One peaceful afternoon while sitting on a small island in a dam, I was watching the large numbers of aquatic insects, and was amazed to see how many different insects were able to walk on the water.
Presently, I noticed what looked like a leaf of Kikuyu grass moving beneath the surface. The island on which I was sitting was covered by Kikuyu grass, and at first I thought the leaf was moving with currents of water. However, it continued in a definite direction until it became attached to a growing plant, where it looked just like a piece of underwater vegetation.
By this time, my interest was so aroused that I took up the leaf from the water and, to my amazement, found a wormlike insect inside a tube made from two narrow pieces of Kikuyu leaf sealed together! I then placed the tube in the water, about a yard from the island, to see whether it would find its way back. Sure enough, the ''jet'' pipe moved back to land at some speed and in a purposeful manner.
The method of propulsion used by this strange contrivance eluded me until I took it up and held it against the sun. There the secret was revealed - the worm , by gyrating its body in the grass ''tube'' with a circular and extending motion, sucked water into and through the tube to provide the jet stream - a remarkable use in Nature of the principle of the Archimedean screw for propulsion!