How Light Affects Earthworms

Earthworms are affected strongly by light, and even more strongly by sunlight in particular. This is due to their anatomical structure, and it is certainly a protective mechanism. It is unclear whether or not the light itself causes pain; it is possibly the fact that the light may be a precursor to death that motivates the reactions of earthworms. This natural reaction to light can be used to a worm-keeper's advantage.

  1. Anatomy

    • Earthworms cannot see, but they have light-receptive cells scattered over the lengths of their bodies. These cells are most prevalent at either end of their bodies, although there are a few scattered in between as well. They are incredibly sensitive to light, reacting in proportion to a light's strength.

    Time Frame

    • Upon sensing light at either end of their bodies, earthworms react immediately. If exposed to ultraviolet light (such as full sunlight) for extended periods of time, they may die.

    Effects

    • Exposure to strong light at either end of an earthworm causes it to immediately seek shelter by burrowing. If no material (soil, or bedding, if the earthworm is being kept inside) is available for burrowing, the earthworm will try to get away from the light as quickly as it can. This will involve extremely fast contraction of its rings in order to shimmy away. If it feels particularly threatened, it may curl up into a knot to try to wait out the threat posed by the light.

      If the light is trained on the central portion of the earthworm, it may be confused and begin moving in sideways motions and seemingly random patterns. This may be because earthworms do not have as many light-receptive cells in the middle segments of their bodies.

    Considerations

    • It is unclear whether it is the light itself that causes earthworms such discomfort, or the heat which often accompanies light. Earthworms do not have lungs, and so must breathe through their skins, taking oxygen directly into their bodies through moisture. It is for this reason that their preferred environments are moist, but not so moist that they drown.

    Benefits

    • If environmentally concerned individuals keep earthworms for worm composting purposes, the earthworms' inherent discomfort under bright lights can be used to control them. Worms in a worm bin may crawl wherever they choose while it is dark. Individuals keeping worm bins may not want them to go certain places, such as outside their designated worm bins. These individuals can use bright lights to coax the worms into burrowing down into their bedding, rather than trying to escape or go exploring.