This section is from the "The New Student's Reference Work Volume 5: How And Why Stories" by Elinor Atkinson.
Once upon a time a baby was born. It was a very, very small baby, and almost too feeble to move. Yet, the very first day of its life, it ate two hundred times its own weight. As long as it lived it ate as greedily as that. It was nearly all mouth and stomach. Every day or two it outgrew its own skin. The skin split down the back, the baby crawled out in a new and larger skin, and went right on eating. It seemed never to sleep. In a few weeks it changed its skin five times. When it was grown up it was ten thousand times as big as when it was born.
What a monster! If this were a human baby, it would have eaten a pile of food as big as a ton of coal the first day. And, when fully grown, it would have weighed one hundred thousand pounds. Is this a giant story, like that of the Brob'ding-nag'ians in Gulliver's Travels? No, it's a really, truly story, but the monster babies are more like the Lilliputians. They were the tiny people, who swarmed all over Gulliver when he was asleep, and tied him up tight with cobwebs or something. Our Lilliputian enemies are caterpillars and grubs. They are hatched, many of them, from pinhead eggs, and they grow to hundreds and even thousands of times as big as when they come out of the eggs.
"Once upon a time" is right now, and all the time. You can find these monster babies on every lawn, in every garden and park and farm, on the grass, on small plants and big trees; buried in soft fruits and hard grains, and in tunnels they have bored in roots and stems and tree trunks. You can see their fathers and mothers flying in the air, too They are beautiful butterflies and moths, shiny beetles and gauzy-winged flies. How pretty they are, and they don't seem to be doing any harm at all.
So long as they have wings few insects eat much, and most of them live only a short time. But the females are busy laying eggs. That little gray moth, half an inch across the wings, that you see hovering over the pink apple blossoms, lays an egg that hatches into the apple worm. The fat white grub eats its way through, spoils the apple and crawls out. It spins a rough cocoon, just the color of the tree, and under a scale of bark. There it lies all winter, coming out as a moth, in the spring, to lay more eggs in the blossoms, to spoil more apples.
All insects go through this larva stage. Then they do nothing but eat. Bees feed their babies with honey, so they do no harm at all, and are very useful to us. But most insects die when they have laid their eggs, and they leave their greedy babies to eat plants that men work so hard to grow. They always lay the eggs where the larva can find their favorite food, and they lay hundreds and even thousands of eggs, most of them too small for you to see.
When the eggs of butterflies, moths and flies hatch, they come out as caterpillars with six legs, hairy or smooth worm-like bodies and chewing mouths. The larva of beetles are usually footless grubs. Some of them look much like the parent insects, but are less active. They all begin to eat ravenously. Inside there is little but stomach and material for making cocoons. Leaf-eaters grow to full size in a few weeks. Orchard fruit and nut eaters stay in the fruits until they fall. The larva of some boring beetles live in the wood of trees for two or three years. They honey-comb solid trees with little tunnels.
When grown to full size the larva of all insects spin cocoons or make horny or papery cases. Some roll up in leaves, using a very little silk to close the openings. They use the hairs from their own bodies, sometimes, to mix with silk, or with plant fibres. These cocoons nestle in the ridges of bark, hang from stems or leaves, or lie in the ground. Cocoons are often so near the color and texture of the thing they are fastened to, that you may look at hundreds of them and never see them at all.
There is no living plant or animal that these little creatures do not prey upon. As insects they sting, suck blood and sometimes kill the higher animals. But it is as grubs and caterpillars that they eat and injure millions of dollars worth of grains and fruits and garden crops every year.