# worms (not a computer question)

**URL:** <https://boards.straightdope.com/t/worms-not-a-computer-question/397944>\
**Category:** Factual Questions\
**Created:** [March 29, 2007, 5:17am UTC](https://boards.straightdope.com/t/worms-not-a-computer-question/397944 "2007-03-29T05:17:36Z")\
**Posts on this page:** 5\
**Page:** 1

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**Author:** ![justwannano](https://avatars.discourse-cdn.com/v4/letter/j/7ab992/32.png) [@justwannano](https://boards.straightdope.com/u/justwannano)\
**Post date:** [March 29, 2007, 5:17am UTC](https://boards.straightdope.com/t/worms-not-a-computer-question/397944/1 "2007-03-29T05:17:36Z")

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I just got back inside after picking a few dozen night crawlers for a fishing trip I’m going on this weekend. I never have figured why a critter who has no eyes can sense light . Those critters are quite quick retreatring into their hole when a light is shined on them.  
How do night crawlers sense light?

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**Author:** ![zoogirl](https://avatars.discourse-cdn.com/v4/letter/z/b9bd4f/32.png) [@zoogirl](https://boards.straightdope.com/u/zoogirl)\
**Post date:** [March 29, 2007, 5:50am UTC](https://boards.straightdope.com/t/worms-not-a-computer-question/397944/2 "2007-03-29T05:50:20Z")

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I think they do have some sort of very rudimentry eyes. At least, a sensory system capable of “seeing” light and dark. They may also be able to pick up very slight tempature changes but I’m kind of WAG - ing here.

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**Author:** ![tomndebb](https://avatars.discourse-cdn.com/v4/letter/t/b9e5f3/32.png) [@tomndebb](https://boards.straightdope.com/u/tomndebb)\
**Post date:** [March 29, 2007, 6:33am UTC](https://boards.straightdope.com/t/worms-not-a-computer-question/397944/3 "2007-03-29T06:33:11Z")

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Not a direct answer, but [this excerpt from the PBS series _Evolution_](http://www.pbs.org/wgbh/evolution/library/04/4/text_pop/l_044_01.html) has some interesting information on eye development.

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**Author:** ![yabob](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/yabob/32/2821_2.png) [@yabob](https://boards.straightdope.com/u/yabob)\
**Post date:** [March 29, 2007, 6:37am UTC](https://boards.straightdope.com/t/worms-not-a-computer-question/397944/4 "2007-03-29T06:37:23Z")

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They do have some light sensory cells in their skins, although no ability to form a visual image. Less sensitive to the red end of the spectrum. Avoiding light is obviously a useful behavior for a creature that must avoid drying out or it will suffocate.

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**Author:** ![vetbridge](https://avatars.discourse-cdn.com/v4/letter/v/b5e925/32.png) [@vetbridge](https://boards.straightdope.com/u/vetbridge)\
**Post date:** [March 29, 2007, 3:38pm UTC](https://boards.straightdope.com/t/worms-not-a-computer-question/397944/5 "2007-03-29T15:38:25Z")

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Many organisms have photoreceptors without having “eyes”.