Worms have long soft cylindrical bodies and no legs. They range in size from microscopic to 22-foot long African giant earthworms and 180-foot marine nemertean worms. Most people are familiar with earthworms, but there are different types of worms that can be found on land, in freshwater and marine environments, and even as parasites inside other creatures. Earthworms have been around for about 120 million years and have primitive sensory systems, with no eyes.
Worms are primitive creatures with no limbs, eyes or ears to provide them with sensory information about their environment. They have sensory receptors in their skin that are sensitive to vibrations, touch, chemicals and light. These receptors transmit information to a very primitive and simple brain that directs their body movements in response to the sensory information provided.
How Worms Sense Light
Light-sensitive receptor cells in the worm’s skin, especially at their front end, allow the worms to register the presence of light, even though they have no eyes. According to Cornell Composting, worms become paralyzed if they are exposed to light for about an hour or more. They can detect both light and changes in the intensity of the light.
Why Worms Need to Sense Light
Worms breathe through their soft, moist skin. If their skin dries out they can no longer breathe and they will die. They spend most of their life in the top 6 inches of moist soils, and avoid sunlight because it will dry them out, exposing them to predators, such as birds. They need to sense light so that if they become wholly or partially exposed to the sun as they are tunneling, they can move back into the soil.
Worms Respond to Different Colored Lights
Experiments have shown that worms respond differently to various visible light wavelengths. They move away from white or blue light, but do not react to red light, such as a red light bulb placed above their environment. If you go out at night searching for worms you will have more success if you use a light with a red bulb, or a red filter across the lens.