In the end, Eliza laid a large number of eggs in a silken cocoon, in shape a balloon, and secreted, like the web, by her invaluable spinnerets. Indeed, the real reason--I won't say excuse--for the rapacity and Gargantuan appetite of the spider lies, no doubt, in the immense amount of material she has to supply for her daily-renewed webs, her home, and her cocoon, all which have actually to be spun out of the assimilated food-stuffs in her own body; to say nothing of the additional necessity imposed upon her by nature for laying a trifle of six or seven hundred eggs in a single summer. And, to tell the truth, Lucy and Eliza seemed to us to be always eating. No matter at what hour one looked in upon them, they were pretty constantly engaged in devouring some inoffensive fly, or weaving hateful labyrinths of hasty cord round some fiercely-struggling wasp or some unhappy beetle.
We weren't fortunate enough, I regret to say, to see Eliza's eggs hatch out from the cocoon; but in other instances, especially in Southern Europe, I have noticed the little heap of well-covered ova, glued together into a mass, and attached to a branch or twig by stout silken cables. If you open the cocoon when the young spiders are just hatched, they begin to run about in the most lively fashion, and look like a living and moving congeries of little balls or seedlets. The common garden spider lays some seven hundred or more such eggs at a sitting, and out of those seven hundred only two on an average reach maturity and once more propagate their kind. For if only four lived and throve, then clearly, in the next generation, there would be twice as many spiders as in this; and in the generation after that again, four times as many; and then eight times; and so on _ad infinitum_, until the whole world was just one living and seething mass of common garden spiders.
What keeps them down, then, in the end to their average number? What prevents the development of the whole seven hundred? The simple answer is, continuous starvation. As usual, nature works with cruel lavishness. There are just as many spiders at any given minute as there are insects enough in the world or in their area to feed upon. Every spider lays hundreds of eggs, so as to make up for the average infant mortality by starvation, or by the attacks of ichneumon flies, or by being eaten themselves in the young stage, or by other casualties. And so with all other species. Each produces as many young on the average as will allow for the ordinary infant mortality of their kind, and leave enough over just to replace the parents in the next generation. And that's one of the reasons why it's no use punishing Lucy and Eliza for their misdeeds in this world. Kill them off if you will, and before next week a dozen more like them will dispute with one another the vacant place you have thus created in the balanced economy of that microcosm the garden.