"Work out your own salvation."—Paul.
"Any new set of conditions occurring to an animal which render its food and safety very easily attained, seem to lead as a rule to degeneration."—E. Ray Lankester.
Parasites are the paupers of Nature. They are forms of life which will not take the trouble to find their own food, but borrow or steal it from the more industrious. So deep-rooted is this tendency in Nature, that plants may become parasitic—it is an acquired habit—as well as animals; and both are found in every state of beggary, some doing a little for themselves, while others, more abject, refuse even to prepare their own food.
There are certain plants—the Dodder, for instance—which begin life with the best intentions, strike true roots into the soil, and really appear as if they meant to be independent for life. But after supporting themselves for a brief period they fix curious sucking discs into the stem and branches of adjacent plants. And after a little experimenting, the epiphyte finally ceases to do anything for its own support, thenceforth drawing all its supplies ready-made from the sap of its host. In this parasitic state it has no need for organs of nutrition of its own, and Nature therefore takes them away. Henceforth, to the botanist, the adult Dodder presents the degraded spectacle of a plant without a root, without a twig, without a leaf, and having a stem so useless as to be inadequate to bear its own weight.
In the Mistletoe the parasitic habit has reached a stage in some respects lower still. It has persisted in the downward course for so many generations that the young forms even have acquired the habit and usually begin life at once as parasites. The Mistletoe berries, which contain the seed of the future plant, are developed especially to minister to this degeneracy, for they glue themselves to the branches of some neighboring oak or apple, and there the young Mistletoe starts as a dependent from the first.
Among animals these lazzaroni are more largely represented still. Almost every animal is a living poor-house, and harbors one or more species of epizoa or entozoa, supplying them gratis, not only with a permanent home, but with all the necessaries and luxuries of life.
Why does the naturalist think hardly of the parasites? Why does he speak of them as degraded, and despise them as the most ignoble creatures in Nature? What more can an animal do than eat, drink, and die to-morrow? If under the fostering care and protection of a higher organism it can eat better, drink more easily, live more merrily, and die, perhaps, not till the day after, why should it not do so? Is parasitism, after all, not a somewhat clever ruse? Is it not an ingenious way of securing the benefits of life while evading its responsibilities? And although this mode of livelihood is selfish, and possibly undignified, can it be said that it is immoral?
The naturalist's reply to this is brief. Parasitism, he will say, is one of the gravest crimes in Nature. It is a breach of the law of Evolution. Thou shalt evolve, thou shalt develop all thy faculties to the full, thou shalt attain to the highest conceivable perfection of thy race—and so perfect thy race—this is the first and greatest commandment of nature. But the parasite has no thought for its race, or for perfection in any shape or form. It wants two things—food and shelter. How it gets them is of no moment. Each member lives exclusively on its own account, an isolated, indolent, selfish, and backsliding life.
The remarkable thing is that Nature permits the community to be taxed in this way apparently without protest. For the parasite is a consumer pure and simple. And the "Perfect Economy of Nature" is surely for once at fault when it encourages species numbered by thousands which produce nothing for their own or for the general good, but live, and live luxuriously, at the expense of others?
Now when we look into the matter, we very soon perceive that instead of secretly countenancing this ingenious device by which parasitic animals and plants evade the great law of the Struggle for Life, Nature sets her face most sternly against it. And, instead of allowing the transgressors to slip through her fingers, as one might at first suppose, she visits upon them the most severe and terrible penalties. The parasite, she argues, not only injures itself, but wrongs others. It disobeys the fundamental law of its own being, and taxes the innocent to contribute to its disgrace. So that if Nature is just, if Nature has an avenging hand, if she holds one vial of wrath more full and bitter than another, it shall surely be poured out upon those who are guilty of this double sin. Let us see what form this punishment takes.