How Do Earthworms React to Light and Dark?

Earthworms react negatively to light, avoiding it entirely when possible, because prolonged sunlight paralyzes and ultimately kills them. Earthworms thrive in darkness and live healthy lives without ever seeing the sun.

Earthworms have no eyes; they differentiate between light and dark by using their anterior, or front end, which is highly sensitive to temperature changes. Earthworms do not like light; they are cold-blooded and quickly overheat in sunlight. Overheating causes their slimy coating to slowly dry out, which allows them to dehydrate and kills them. Earthworms in warm areas quickly take cover in a cooler area or die trying.

Earthworms prefer their damp, cool home beneath the earth and can live out their entire lives without coming above ground. Worms are normally seen above ground in warmer months, but not because they want to be above ground; flooding caused by heavy rains, melting snow and other sources drive worms from their homes. The waterlogged earth forces them to breach the earth's surface or drown. Others are dug up by animals or people and must find, or dig, a new path below ground. Worms have no lungs and breathe through their skin; if submerged in water for too long they drown.