This section is from "The Horticulturist, And Journal Of Rural Art And Rural Taste", by P. Barry, A. J. Downing, J. Jay Smith, Peter B. Mead, F. W. Woodward, Henry T. Williams. Also available from Amazon: Horticulturist and Journal of Rural Art and Rural Taste.
The Ichneumon animal eats the eggs of the crocodile, to some extent controlling its numbers.
The cuckoo in England and the cow bunting in this country, lay their eggs in the nests of other birds, and the young are nurtured by foster mothers; and it is said these parasite intruders have the instinct to throw the rightful possessors out of their nests. By such a process these foster parents would be lessened the next year - a law that would react upon the parasites in the future; and we see that none of these birds become numerous. The ichneumon insect is a four-winged fly, and an immensely numerous class, of all sizes and exceedingly irregular and eccentric in shape. They are the great regulators of insect life.
The female deposits her eggs in, and the young feed upon, the living bodies of other insects.
It is the fatal enemy of many other insects; flies in their larva state, and even the eggs of some insects, are destroyed by them, but the caterpillars are the great sufferers. You may often see feeble looking ones, studded over the back with little protuberances; these are the cocoons of the parasite grubs that have fed to maturity upon the flesh of the poor worm, and leaving just vitality enough to last as long as it is necessary for them that they should live. These little creatures, when full grown, issue from the substance of the poor caterpillar, spin their cocoons and attach them by silken cords to their miserable victims. (Here the Doctor showed a specimen with eighty cocoons attached, and from which he had collected the flies).
Many insects prey upon each other; sometimes diseases diminish them; birds destroy incredible numbers; toads eat them; frogs and fish consume vast numbers of the larva of the submarine varieties; but such is the incredible rate of increase, that many kinds would overrun us, but for the wonderful check of this parasite class. The newspapers often report fearful numbers of some new insect, and forebode dreadful consequences. Such insects are troublesome for a short time and then disappear. Some observe a periodicity, as the Locust, the Chaffers, and Ephemerae, but most of them are checked by the Ichneumon.
I have seen the stems of grapes cut off in great numbers by a caterpillar, and I attempted to see what butterfly it would come to, but I only got large, fierce looking Ichneumon flies, two from each.
Our pine forests are saved from serious injury, and the lumber from damage, by the friendly interference of an Ichneumon insect that stings the borer, while just under the bark, during the period of its transformation.
I once knew an ecceutric person make a calculation, that the undisturbed increase of a single herring would, in twenty years, more than equal the solid earth, and he became nervous with the idea that we were all to become herrings. He forgot that in addition to the hundreds of enemies that prey upon these fish, besides ourselves, that the cachelot whale feeds upon them, and takes in 2,000 at a single mouthful. No. Nothing here is allowed to take exclusive possession. Of the hundreds of thousands of varieties of insects, none become extinct, and none are permitted to preponderate to a dangerous degree for any length of time.
When meteors and comets jostle the planets out of their places, and the heavenly system becomes disturbed, it will be time enough to anticipate that God has forgotten to regulate the insect world.