Subsurface Locomotion

<-NARRATOR:-> Listen to part of a lecture from a biology class.
<-FEMALE PROFESSOR:-> When we humans walk from place to place, we move on the Earth's surface,
across the Earth's surface.
Many animals, of course, do the same thing -
horses, and dogs, and cows, and so on all move on the surface,
across the surface of the earth....
But there are also quite a few animals that have the ability to move from place to place underground,
beneath the earth's surface.
This moving around underground is known as subsurface locomotion.
Subsurface locomotion has a number of benefits.
One benefit of subsurface locomotion
is that it enables animals to minimize their exposure to extreme temperatures.
This is very helpful for animals that live in areas with harsh climates,
where it could be very dangerous to spend large amounts of time on the surface.
For example, in the Sahara Desert, in Africa,
there's a type of lizard that's able to move beneath the surface-
through the sand-very quickly.
Because this lizard can move so easily and so quickly underground,
it doesn't have to travel on the surface,
where it would be exposed to dangerously high temperatures.
Another benefit of subsurface locomotion
is that it can help animals capture prey.
That's because animals on the surface
can't see predators that are approaching underground.
Our lizard in the Sahara Desert is again a good example.
The way it works is,
when an insect is walking nearby on the surface,
it produces very subtle vibrations in the sand.
When the lizard senses these vibrations,
it moves very quickly - underground,
where it can't be seen -
toward the source of the vibrations.
It then suddenly pops up right under the insect,
and catches it completely by surprise.