The armadillo jumps because he is surprised.
Here
is a
photograph of an actual armadillo caught in mid-jump!
Armadillos prefer to defend themselves by: diving into their burrows, hastily
digging a new burrow, and the best known defense, rolling into a ball.
In addition to these behaviours, sometimes when they are surprised, they will
jump straight up. Unfortunately, this is no defense against automobiles, their main Texas
predator!