Popular Science Monthly/Volume 1/September 1872/The Enemies We Import
|←On Moral Contagion||Popular Science Monthly Volume 1 September 1872 (1872)
The Enemies We Import
IT would seem as if every grain brought its bane. The Agricultural Department at Washington has done a good deal for agriculture in the importation and distribution of foreign seeds, slips, and plants. In this way have been secured to the country many of the choicest improved plants from abroad, and many entirely new to our gardens. But it is to be feared that, in some instances unavoidably, and in others from want of care or skill, or both, the eggs and larvae of foreign insect-pests have been introduced, and are today troublesome to the husbandman, and a source of mischief and loss to the interests of the nation at large. If that man, or that art, is a public blessing that makes a spear of wheat grow where the land was sterile before, or makes that bear twofold that before did little more than barely reproduce its kind, surely, then, that is a pest and misfortune that appears as a new destroyer of the anticipated harvest. So far as size is considered, the little fly introduced in the provender of the Hessian soldier, in 1776, is contemptible; yet it was destined to become an enemy more formidable than the troops that brought it. So diminutive, indeed, is this pest, that many a husbandman has never seen it to know it, and, in fact, only knows it from its sad depredations on his honest labor; which are such that all the combined whirlwinds and destructive storms that have ever swept over portions of our land have not robbed the national wealth so much as this almost invisible, tiny creature, that dances in the sunbeam; which science well names Cecidomyia destructor, and which tradition calls the Hessian fly.
In Freehold, N. J., in the autumn of 1870, 1 detected a new-comer making terrible havoc with the cabbage. This esculent was entered from without, and almost honey-combed by a small green caterpillar, that I had never seen before. It was soon determined to be the Pieris rapae, or cabbage-caterpillar of Europe. The parent was a pretty butterfly, mainly white, with black spots on the wings. It first appeared on this continent at Quebec, and made its noxious power felt in the destruction of the cabbages to the amount of many thousands of dollars in that neighborhood. It soon came into Northern New England, and in 1869 was found in the gardens within a few miles of New York. At Freehold, of course, it was stretching south. It soon reached Philadelphia. Last summer it was at home at Baltimore, and this June it has appeared at Washington. The terrible little beauty is thus belting the land with a scourge.
Among the insect pests that have become celebrated because of its fearful capacity of increase, the grasshopper deserves mention. It is well known that in Russia this insect appears in such prodigious numbers that the wheels of the vehicles roll crushingly through the masses. Mr. Glover, the entomologist of the Department of Agriculture, states that a new grasshopper has appeared. Besides several larvæ and part of an entire insect found when cleansing the pots in the greenhouse of the department, a pair of these strange creatures, a male and a female, has been obtained. They went lustily to work on the leaves of the coffee-plant, bananas, etc., in the greenhouse, "much in the same manner as is done by our native katydids, by eating holes in the leaves and gnawing away the edges. Their jaws were remarkably strong and sharp, and when the insects were incautiously handled they bit so severely as to draw blood. The male was about 1.75 inch in length from the tip of the cone, or horn on its forehead, to the end of its wing-covers when closed. The female measured 3.05 inches to the end of the ovipositor, which itself was at least 1.25 inch in length. The general color of both male and female was a light pea-green, and the wings were delicately veined with distinct nerves, resembling the venation of leaves. A very marked feature in this insect, when alive, is that the labrum and clypeus are bright yellow, contrasting strongly with the jet-black of the mandibles, which, together with the cone or horn on the top of its head, gives it a remarkable appearance. This cone or horn, which is placed obliquely upward on the top of the forehead, forming a line with the face, is yellow beneath, black at the tip, and ends in an acute point, which is somewhat bent downward at its summit. No insect resembling it having hitherto been found in this neighborhood, there is but little doubt that it has lately been imported with or on some foreign plants sent from South America, or the West Indies; and, as many exotic plants have been received from Balize, British Honduras, it is probable that this grasshopper came in the egg-state, on some of the plants from that locality, and was hatched out last summer in the greenhouse. This fact alone admonishes us how careful we should be when importing new and valuable plants from abroad, for, if a large insect, nearly two inches in length, and fully the size of a katydid, can be so easily introduced, how much more readily the small and inconspicuous noxious insects hidden under the bark would be likely to escape notice, until they had perpetuated their species, so as to become partially naturalized and injurious to our plants! There is no danger, however, that this grasshopper will spread, and, as it is apparently very tender and accustomed to a tropical climate, most probably it would not be able to withstand the rigors of our winters in the open air, and as all were killed or caught as soon as seen in the greenhouse, there is very little probability of any being left to perpetuate their race." Mr. Thomas has described this insect under the name of Copiophora mucronata, in the "Canadian Entomologist."
More curious and perhaps more interesting to scientific consideration is the appearance, in the hot-houses of the Agricultural Department, of a new earth-worm. The species is very large, and, compared with our common angle-worm, it is very curious. It has multiplied in the hot-houses of the department so as to have become a real pest. It is believed to have been introduced from Japan in the earth with the plants imported in the expedition under Commodore Perry. Mr. Glover seems to think it is the same as the worm now doing much damage to pot-plants in the hot-house conservatories of England, and quotes Mr. Fish in the English Gardener's Chronicle, who speaks of "the eel-worm" as "probably a tropical relation of the common earth-worm, as it cannot live out-of-doors in the climate of England, and scarcely subsists in a greenhouse, but revels in the temperature of a plant-store or orchideous house. It differs from the common worm in its mode of locomotion, and in several of its habits. It comes out at night on walls, stone floors, etc., and is as quick as an adder in its movements when disturbed. It seems impossible to eradicate it; it appears to breed with extraordinary rapidity, and is endowed with great muscular power, so much so that it is somewhat difficult to hold a large specimen between the thumb and finger. Lime-water, which is a sovereign remedy against the common earth-worm, appears to have little influence on it, and the only effective mode of destruction is to turn out the soil from the pot and catch and kill the intruder, taking care, however, not to knock or jar the plant, as this worm, instead of coming to the surface on being disturbed, like the common worm, will instantly recede to the centre of the ball of earth and remain there undisturbed. Mr. W. Baird speaks of a worm under the name of Megascolex (Perichæta) diffringens, found in three different gardens in England, in hot-stove houses, which is probably the same as the eel-worm referred to by Mr. Fish."
If, in the blatant ethics of the pot-house politician, "eternal vigilance is the price of liberty," in a sense certainly of equal importance it behooves that, even in disseminating these matters for the common good, science should dictate the method, and the economist practise the care that shall conserve the good while it separates the bad. But only of its best and noblest minds can the age exact the task of separating wisely and well its blessings and its bane.