How Does an Earthworm React to Light & Darkness?
While earthworms move away from bright white light, they ignore reddish light and are attracted to dim light. "The advent of evening calls (earthworms) forth from their burrows," notes Frank E. Bedard, since their "more active enemies above ground" are not present.
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Features
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The back of earthworms, as well as their prostomium, a lobe of tissue overhanging the mouth that the worm uses to probe its surroundings, contain light-sensitive cells called photoreceptors. Thus worms can sense light, even though they do not have eyes.
History
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In 1903, George P. Adams examined how earthworms respond to light. "Earthworms retreat toward their burrows during the daytime because of their negative phototropism," or orientation to light, he wrote. "They emerge at night not so much because of darkness as because of their positive phototropism for faint light," he wrote.
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Theories/Speculation
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Photoreceptors on an earthworm's body allow it to turn away from brightness, which signifies daytime hazards such as the sun's ultraviolet light, excessive heat or robins on the prowl. The worm escapes in the direction of darkness.
Fun Fact
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Charles Darwin noted of earthworms that while they prefer to mate in the darkness, "their sexual passion is strong enough to overcome for a time their dread of light."
Expert Insight
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"If earthworms are exposed to light for too long (about an hour), they will become paralyzed and die when their skin dries out," according to Rhonda Sherman, extension specialist at North Carolina State University.
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References
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- Photo Credit Image by Flickr.com, courtesy of Prabhu
