Each year, earthworms move deep into soil during fall and winter and return toward spring and summer. what is the likely stimulis for this behavioral response

Each year, earthworms move deep into soil during fall and winter and return toward spring and summer. The likely stimulis for this behavioral response are relative humidity & temperature. Since the nematode breathes via the skin, the mucus coating may become dry & the organism would die if exposed to extreme cold & dryness.