How is earthworm behavior affected by external stimuli?”

They tend to move away from any stimulus be it light or mechanical.

Explanation:

The earthworm, upon encountering a stimulus that is mechanical in nature will turn its anterior end slightly away from the stimulus. Persistence of the stimulus may cause the worm to contract the longitudinal muscles of the opposite side to move the body around taking a new direction. And they also have the behaviour of tending to move away from any light stimulus.

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