Anonyme, Chatty Reading in Elementary science, New York, Longmans, Green & Co., 1901, p .55-59
An insect disguise
- Two boys were walking one pleasant summer daya long the banks of a little stream. Suddendly one of them stopped and began to stare at the water.
- « What are you looking at ? » inquired the other boy.
- « Just look at taht bit of gravel on the top of the water. Did you ever sse gravel float before, »
- « Never, But look again ! Why, it is moving against the current of the stream ! Can you understand that ? »
- « No. But I’ll soon find out what it all meams ! » And without another word he took off his shoes and stocking, waded into the water, and caught the strange little craft in his hand.
- When brought to land the prize was eagerly examined by the two boys. They found it to be round, and about an inch in length. But it was no all gravel ; for from one end there peeped out a little horny head and six slender legs.
- « Oh ! it’s alive ! Why, it’s like an insect plastered all over with a coat of dirt ! » exclaimed one. Then the boys wanted to know all about this strange little sailor. So they carrioed it to their father, who knew a great deal about insect life.
- « It is a caddis-worm, » said he. « If it lives long enough i twill turn into a caddis-fly-one of those delicate insects with large brown wings which you may seen along the brookside. »
- « But how di dit get covered with gravel like this ? » asked the boys.
- « The stream you know, has a gravelly bed, and the caddis-worm got, these bits of stones from the bottom of the stream, and stuck them all together with liquid glue from its own mouth. Many caterpillars the silkworm for instance, can produce a gummy liquid which hardens into silky threads.
11 »If you examine the caddis-case, you will see that it is a little hollow tube of gravel, lined inside with silk to make it comfortable. »
- « But how di dit make the gravel to float on the top of the water ? And why di dit want to make such a strange rough-looking coat of armor at all ? »
- « It will tell you. No doubt you wondered when you saw grit floating on the top of the water. Here is the secret of that wonder. You will notice that the little creature has made his case light enough to float by building a bit of twig into it. You may also observe that this « float » keeps at the top, and projects over at one end as a protection to the head.
- »The strange covering is not so heavy as it looks, and he can draw it along wherever he goes in his search for water-plants and small insects ; he can float i tat the top or sin kit to the bottom, whichever he wishes.
- « As to the reason for all this, the creature does it as a protection against the fishes and the numerous other enemies that are always lying in wait to devour him. In disguising himself as a bit of gravel he certainly deceived you, and hoped in the same way to escape the notice of his enemies.
- » Had the brook possessed a sandy bottom the caddis-case would then have been built of sand. A friend of mine kept some caddis-worms in glass jars covering the bottom of each jar with a different material. The caddis-case were consequently built of a different material in each jar. In each jar it was impossible to distinguis the caddis-case as it lay on the bottom amidst the other material.
- « I went to see one little creature at work. He got together the bits with which he was surrounded, and after outting them into the right position, stuck them firmly together with a few licks.
- » When full-grown, the caddis-worms fasten their cases to a stone or a water-weed, close up the ends with silk, and turn into chrysalides.
- « After a time, having thus cleverly escaped life’s dangers, they move to the surface of the water, and out creep, those pretty little four winged caddis-flies. »
- « Well, » said the elder boy, « it seems to me that the caddis-worm knows how to play a very good game of « Hide and Seek » with its enemies ! »