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Why do earthworms avoid strong light?
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The structure of polychaetes. (Left) Free-moving polychaetes. (A) Neanthes, (B) Nereis. (Right) Tube-dwelling (sedentary) polychaetes. (C) Amphitrite, (D) Sabella.
Earthworms do not have eyes and cannot see, but they are highly sensitive to light. While they lack the complex photoreceptors found in many other animals, their bodies possess a sensitivity that allows them to detect light stimulation.12
This sensitivity is a survival mechanism; because earthworms are invertebrates that thrive in moist, soil-rich environments, exposure to strong light can be harmful or fatal, often leading to desiccation. By avoiding light, they remain in the protective, damp conditions of the soil necessary for their respiration and overall health.1