How Do Earthworms Respond to Light?
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The Blind Earthworm
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Earthworms retreat from light. The worms you see above ground during storms have often come above ground as a result of flooding, not out of any fondness for being out and about in broad daylight. Instead, earthworms live up to the nickname of one of their families: they're night crawlers, avoiding strong light and only coming to the surface in darkness.
Light Sensitive Cells
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Earthworms may not have eyes, but that doesn't mean they don't see--or, at least, that they don't sense light. Earthworms have photosensitive cells scattered around the skin of their bodies, particularly near the head-end. When a worm comes close enough to the surface for light to filter through grass and surface soil the worm's light detecting cells "see" the sunshine and the worm retreats back down into the ground where it is safe and cool and damp.
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Catching Night Crawlers
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For those who love to fish, they know that night crawlers are a challenge to catch. The old fashioned way was at night with a flash-light. The light would be pointed over the earth with just enough reflected light shimmering on the moist skin of the night crawler to spot the worm. Then your best bet to catch the creature was a fast snatch--even the reflected shimmer would send them back under where you couldn't catch them. Now people have updated a bit, and use a flashlight with a red bulb or some form of red filter. This technique works because the photosensitive cells on the worm's skin are less sensitive to red light and the worm is less likely to run from your flashlight beam.
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