Although they are indifferent to undulations in the air audible by us, they are extremely sensitive to vibrations in any solid object.When the pots containing two worms which had remained quite indifferent to the sound of the piano, were placed on this instrument, and the note C in the bass clef was struck, both instantly retreated into their burrows.After a time they emerged, and when G above the line in the treble clef was struck they again retreated.Under similar circumstances on another night one worm dashed into its burrow on a very high note being struck only once, and the other worm when C in the treble clef was struck.On these occasions the worms were not touching the sides of the pots, which stood in saucers; so that the vibrations, before reaching their bodies, had to pass from the sounding board of the piano, through the saucer, the bottom of the pot and the damp, not very compact earth on which they lay with their tails in their burrows.They often showed their sensitiveness when the pot in which they lived, or the table on which the pot stood, was accidentally and lightly struck; but they appeared less sensitive to such jars than to the vibrations of the piano; and their sensitiveness to jars varied much at different times.
It has often been said that if the ground is beaten or otherwise made totremble, worms believe that they are pursued by a mole and leave their burrows.From one account that I have received, I have no doubt that this is often the case; but a gentleman informs me that he lately saw eight or ten worms leave their burrows and crawl about the grass on some boggy land on which two men had just trampled while setting a trap; and this occurred in a part of Ireland where there were no moles.I have been assured by a Volunteer that he has often seen many large earth-worms crawling quickly about the grass, a few minutes after his company had fired a volley with blank cartridges.The Peewit (Tringa vanellus, Linn.) seems to know instinctively that worms will emerge if the ground is made to tremble; for Bishop Stanley states (as I hear from Mr.Moorhouse) that a young peewit kept in confinement used to stand on one leg and beat the turf with the other leg until the worms crawled out of their burrows, when they were instantly devoured.Nevertheless, worms do not invariably leave their burrows when the ground is made to tremble, as I know by having beaten it with a spade, but perhaps it was beaten too violently.
The whole body of a worm is sensitive to contact.A slight puff of air from the mouth causes an instant retreat.The glass plates placed over the pots did not fit closely, and blowing through the very narrow chinks thus left, often sufficed to cause a rapid retreat.They sometimes perceived the eddies in the air caused by quickly removing the glass plates.When a worm first comes out of its burrow, it generally moves the much extended anterior extremity of its body from side to side in all directions, apparently as an organ of touch; and there is some reason to believe, as we shall see in the next chapter, that they are thus enabled to gain a general notion of the form of an object.Of all their senses that of touch, including in this term the perception of a vibration, seems much the most highly developed.
In worms the sense of smell apparently is confined to the perception of certain odours, and is feeble.They were quite indifferent to my breath, as long as I breathed on them very gently.This was tried, because it appeared possible that they might thus be warned of the approach of an enemy.They exhibited the same indifference to my breath whilst I chewed some tobacco, and while a pellet of cotton-wool with a few drops of millefleurs perfume or of acetic acid was kept in my mouth.Pellets of cotton- woolsoaked in tobacco juice, in millefleurs perfume, and in paraffin, were held with pincers and were waved about within two or three inches of several worms, but they took no notice.On one or two occasions, however, when acetic acid had been placed on the pellets, the worms appeared a little uneasy, and this was probably due to the irritation of their skins.The perception of such unnatural odours would be of no service to worms; and as such timid creatures would almost certainly exhibit some signs of any new impression, we may conclude that they did not perceive these odours.