A LIFE HISTORY COLLECTION
You can not collect insects very long before you begin to see a lot of things you never noticed before. You see leaves cut or eaten in strange forms, or you find a cluster of tiny eggs on a leaf, or several leaves sewed or stuck together with strands of silk. Perhaps you find strange abnormal growths on certain plants, swellings on their stems, leaves transformed into balls, or pod-like or cone-like affairs which do not look natural. These things are sure to arouse your curiosity. Sometimes the answer to your question is right there. Cut open a swollen golden-rod stalk and you will find the culprit which caused the plant to grow that way. But how did the footless, helpless grub get there and when? You break down the mud-dauber wasp's nest from among the rafters of some building. What is that yellowish object that rolls from among the ruined adobe walls? Look! It is a spider. What business has a spider in the wasp's nest, if it is her nest? Spiders have none too good a reputation, but this spider does not act very spry. Seems to be alive, yet not alive.
The secret of the relation between the spiders and the wasps you can read in many a book. You might even guess at it, but there was no guess work about the observer who first studied out this secret. He did not get his knowledge from books. He patiently watched the mud-dauber going about her house building. He knew that her painstaking labour could have but one meaning. She was building not a home for herself, but for her children.
The wasp's children are not little wasps, yet they are none the less young wasps for being footless, colourless, wingless, stingless grubs. They are eggs at first of course, just as all insects are. When the mother wasp has one cell of her apartment house finished she concerns herself immediately with stocking the larder. Knowing the tastes of her yet unborn young, she leaves for a time the mud hole, and visits the haunts of certain spiders. Finding one to her liking, she captures it. Not appreciating the fact that the law forbids the use of preservatives in meats, she injects a drop of some wonder-working fluid into the spider and preserves the creature, not only fresh but alive, though paralyzed. Upon the inert body she places an egg, then seals the cell, well assured in her mind that when the grub hatches it will find the food just as she left it and just enough to nourish the young one to maturity.
Before your first season of collecting is past you will find yourself bringing home as specimens many insects which you will see are not fully grown. Little grasshoppers, scarcely bigger than a fly yet possessed of such strength of leg that they can hurl themselves into the air for a distance equal to twenty times their own length. How do you know that they are young grasshoppers and not fully grown ones of some tiny race? Look at one closely and you will see a look of youth about him that is unmistakable. He is fuzzy, his head is too big for him, his legs out of all proportion to the rest of him. Then, too, he has no wings, just little buds where the wings will be some day. By these tokens you will know him for a baby. You can find them in all sizes and can have a series to show the stages of growth. This is one of the first steps in the making of a "Life History Collection," far more valuable to the naturalist than a collection containing only mature insects.
Generally speaking, all adult insects have wings, and all winged insects are adults. There are exceptions to this, but they will take their places when the time comes. The young of the insects belonging to certain orders resemble their parents enough so as to be placed where they belong at a glance. This is true of the grasshoppers, katydids, and crickets, of the true bugs which include the squash-bugs, the chinch-bug, the stink-bug and others. Of most of the other orders this is not true. The young do not look at all like the adults. In many cases as, for example, the dragon fly and the mosquito, they are fitted in the immature stages to a life in the water. They must, on this account, have organs for swimming, for aquatic breathing, and for getting a living in the water. The forms of these young insects are just as varied as those of the adults, but they do not resemble the winged ones in the least. The life history collection must contain specimens of the immature forms of insect life as well as adults if it is to be most useful and complete.
Some orders of insects, as for example the moths, butterflies, beetles, flies, bees, wasps, ants, and others pass through four distinct changes of form. They always follow the same order. Every generation, beginning with the egg, passes next to the larva (called caterpillar or incorrectly worm, or grub, or maggot), on to the pupa, then to the adult. The egg of an insect is often a most beautiful object. With a hand lens, which every collector will surely need, one can see its delicate colouring, its pearl-like shell, its curiously carved or sculptured surface. To get some idea of the great variety in form, colour, shape, and markings of insects' eggs, ask at your library for a book on butterflies, with coloured plates, and the chances are that you will be surprised.
The second or larval stage of the insect's life is the eating, growing stage. During this stage the young bee, butterfly, ant, or moth moults several times. In this process the entire old skin is shed, an operation well worth seeing. Under the old coat a new one has formed, which being larger, accommodates itself to the insect's increased size. The larval stage is in the case of many insects the active time when, if they are vegetable feeders, they injure crops.
When the larva has completed its growth it changes into a pupa. Some insects pass this third stage inside of silken cases they spin about themselves, others, after shedding the larval skin, find themselves each clad in a sort of horny coat of mail. We call these chrysalides. Some larvæ creep away into the ground, there to shed their old coats and rest inside of the pupa cases which nature provides. Each one follows the fashion of his own family and is in no danger of being mistaken for any one else.
Out of the pupa, whether it be cocoon, chrysalis, or just plain pupa case, comes the adult. The main business of adult insects is to reproduce their kind. After the eggs are laid there is little excuse for their living. In the case of a great many kinds of insects death follows soon after. There are some noted exceptions to this rule as for instance the wasps which build with so much skill and patience the homes in which to rear their young, the ants and the bees, both social and solitary, which carry on such a complicated home life. Of these highly "civilized" insects only a word can be spoken here. From the chapter on "Bee-Keeping" and from other books you may learn of the wonders they perform. We must return now to our life history collection.
How the subject opens as we add specimens of cocoons and pupa cases to the collection! To get a complete series illustrating the life, let us say, of one of our common butterflies, the monarch or milk-weed butterfly, you should visit the clusters of milk-weed along the roadside or anywhere, in the forenoon of a sunny July or August day. A few butterflies are probably flitting about in rather casual fashion. Watch them light on the leaves, mark the leaf with your eye and hurry to the spot. Search well. The tiny speck of pale yellow may be a drop of milk but if it stands up on the leaf it is likely to be a butterfly's egg. Your lens will tell you. Having made sure of one you will find others.
You may find a young caterpillar lunching on the leaf. If just out of the egg it is a dull lead colour, but when half grown a young monarch is striped with rings of greenish yellow and black. Though handsome as to colour scheme, this caterpillar has manners unbecoming a plain citizen, let alone a monarch. Touch its back with a grass stem and see what happens.
If time permits you should visit your clump of milk-weed daily or better still take home the eggs and the young caterpillars. Keep the food plant fresh in a jar of water and get more when needed. As you want a specimen of the egg-shell for your collection, you must be on the spot when the young caterpillars come out. They sometimes eat the shell the first thing. It is a delicate operation to glue a thing as frail as this shell onto a dried milk-weed leaf, and you may have to content yourself with making a sketch of it on a small square of drawing paper. Pin the leaf or the drawing in the box. It is not easy to keep specimens of caterpillars. There is a method of preparing the inflated skins, but as the process is a difficult as well as a ghastly one, you can wait till you go to college to learn it. For the milk-weed caterpillar I suggest instead, a coloured drawing. When your caterpillars are full-sized they will transform into chrysalides. It is worth sitting up all night to see a sight like this. When a caterpillar spins a little mat of silk and suspends itself by a tail-hook, you will know that the performance is about to begin. The chrysalis is a lovely light green with spots of gold upon it. All this beauty was hidden under the skin of the caterpillar. With an egg, a caterpillar, a chrysalis, and an adult you have all four stages of the monarch's life represented.