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.
INSECT HOMES
Nothing in the insect world interests me more than their homes. The collector sees many of these in his rounds, and begins to consider how he can complete his series by adding samples of them as specimens to his collection. I was lucky enough to find, when on a collecting trip one day, a curious structure made of mud on a weed stem. It was declared by the professor to be an ants' "cow-shed." Knowing that the museum specimen was in a bad state of repair I readily offered my find to replace it. The professor refused the gift, but offered me what he thought it was worth. I accepted and bought a pair of shoes with the money, which shows that these things have a market value.
It is well to press a specimen of the favourite food plant of a species of insect and make it a part of the collection. But dried butterflies, fastened in utterly unnatural attitudes upon dried plants they would scorn to eat in life, framed or put under glass globes on the parlour table do not appeal to the naturalist. They are "fakes" pure and simple.