There are great swarms of insects which devour or burrow into it, or suck its life-juices. These are infinitely more dangerous than the relatively clumsy, heavy-footed, grazing animal.
Every part of a plant has its own special insect foe, and it is really difficult to understand how it can possibly escape.
Perhaps the "Achilles' heel" is the root, for, underground, plants get no help from the watchful and ever-present army of birds, who are, as we shall see, the natural police of the world.
The Phylloxera, for instance, which ruined the old and valuable vineyards in France, is a terrible little acarid, or mite, which attacks the roots. Too small to see, and impossible to kill without killing the plant, it laid waste the fertile hills and valleys of all South and Central France, causing millions of pounds damage. One reason for this destruction sprang from the universal sporting instinct innate in every Frenchman. Everybody goes out with his gun to destroy any lark, sparrow, or titmouse that is idiotic enough to remain in the country. Only birds can deal efficiently with insect pests. Take this horrible little Phylloxera, for instance; a single female in her life of forty-five days will lay about two hundred eggs. Each egg becomes a little grub, which after a few moments of uncertainty and agitation settles itself, and begins to suck steadily at any unoccupied part of the vine root. After ten to twelve days' life it will be laying eggs as rapidly as its mother. Thus in an ordinary summer the number of young ones produced from a single female becomes quite incalculable.
These pests are natives of America. Imported on American roots about 1868, they had in thirteen years practically ruined the vineyards in France, Spain, Portugal, Italy, and Germany.
All sorts of remedies were tried—saturation of the ground by poisons, flooding the vineyards to drown them, artificial cultivation of their insect and plant enemies, and many others.
The correct and satisfactory method has been at last discovered. American vines of sorts which are able to resist these Yankee mites have been imported, and the valuable French vines have been grafted on to them.
Another very dangerous root-enemy, which is common in this country, is the Cockchafer grub or Whitegrub. (But it is not nearly so bad as in France, where in the summer of 1889, a single farmer collected 2000 lb. of Cockchafers.) The grub (each female lays seventy eggs) burrows into the earth, and for no less than three summers remains below ground devouring indiscriminately the roots of everything he can discover. Underground, the mole is almost his only enemy, but the rooks, starlings, and gulls, which follow the plough, are watching for him. The Wireworm, Clickbeetle, or Skipjack, is also an underground demon which lives for three years, and gnaws and worries at plant roots for the whole of that time. It, however, shows itself above the surface.
A gentleman who had passed his whole life in the country complained, in my presence, of the damage done by rooks. He had had six thousand of them shot that summer, and remarked that he had seen with his own eyes one of them pulling out a young cabbage plant by the root. Of course it was quite unnecessary to point out that the poor bird was merely trying to get at the wireworms and devour them!
For some time I used to look out for great attacks of wireworm in turnip-fields: when one was recorded, I never failed to find that the crows had been ruthlessly shot down a season or two before.