- Published: 18 September 2009
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Mary Anne Krieger, aged 13, for h er question:
What senses does an earthworm have?
The earthworm has no eyes, no ears, no nose and certainly no fingers. Yet he can tell light from darkness. He can sense the vibrations of sound. He has sensations of taste and smell which tell him when food is good to eat and when it is not. He can sense the touch of a robin's bill.
His body is made of two pink tubes, one inside the other. The inner tube is a complex network of living cells. The outer tube is the skin. This skin is banded with thick and thin rings. The family name of the earthworm is Annelids ‑ which means the ringed ones:
We cannot say that the worm has a brain. But it has the simple beginnings of a brain. It has a well organized nervous system. Nerve cells carry messages to and from a sort of central switchboard. This is a cord of nerve fibers and is the worm's simplified brain.
Other nerve cells thread throughout the worm's body. The sense, or sensory, nerve cells reach their tips to the outer skin. They are able to flash certain messages to the central area of the nervous system. The simple brain then sends out orders to the muscles, akin and mouth.
Mr. Worm finds it wise to avoid bright sunlight. For one thing, the sun tends to dry out the moisture from his skin. For another, there are more hungry birds around in the daytime. So the nerve cells in the akin of the earthworm inform him when the light is bright. He acts on this information and retreats to the safety of his dark burrow.
Other nerve endings in the throat inform the worm whether a certain leaf is good to eat or not. These nerve tails parry smell‑taste information. Others respond to the vibrations of a heavy tread. And Mr. Pinky makes for home as fast as a worm can travel ‑which isn't very fast.
Mr. Worm has another trick to keep himself out of trouble. He can lengthen or shorten himself: He can close the rings around his body like a concertina and make himself short and fat. He can stretch the soft skin between them and make himself long. This trick is useful for coping with hungry robins. The worm has two sets of muscles to do this expanding and contracting. One set runs around his body another set runs lengthwise. They are also the muscles with which he crawls along.
So, it seems, Mr. Dinky manages very well for himself ‑ even though he has no eyes to see, no ears to hear, no nose to smell and no fingers to sense touch. He has all the sense he needs to lead a worm's life. And he uses his good sense to do whatever he has to do.