The weight of the insect and structure of
their feet in combination with the surface tension
of water allow some insects to walk on water.
Water molecules are more attracted to each other
than they are to other materials, so they generate
a force to stay together called surface
tension. If the force that the insect foot
makes on the water, is less than the surface
tension of the water, the bug will float. If the
force of the foot is greater than the surface
tension, the bug will sink. What determines the
amount of force the foot generates is dependent on
weight and foot shape. If the foot is flat and
wide, the weight is dispersed across a greater
surface area and the force is less than if the
foot were sharp and thin.
Small animals can run over water because of the
surface tension water has. You can see how
water tension works if you put a drop of water on
a table. The molecules of water in that drop will
stick together to create a dome shape, rather than
lying flat and even on the tabletop.
Water molecules stick together and a force must
be used to surface of the water. While this force
seems small to us, very small animals that don't
weight that much will not create enough force to
separate the molecules. Small insects, spiders,
and even a species of lizard, the basilisk lizard,
are able to take advantage of the surface tension
of water and can move over the water without
sinking into it.
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