Such honey-glands found on the leaves and not connected in any way with the flowers, are more common than one would think. Even the common Bracken produces curious honey-secreting hairs when it is in a young condition. These attract ants which drive away caterpillars and other dangerous insect foes.
Many very dangerous insects are too small for birds, and can only be dealt with effectually by insects or fungi. Of these perhaps the most dangerous are the "scale" insects. The best-known one is very like a minute mussel shell. It is about one-quarter to one-third of an inch long, and can be sometimes found in quantities on apples; they are generally collected round the stalk. The mother insect has this scaly back, and lies down and dies on the top of her eggs, so that her scaly corpse forms a roof and a shield for her young ones. Like all pests of this sort, these creatures increase very rapidly.
A certain scale insect was doing an immense amount of harm in the orange plantations of Fiji, but it was destroyed by the introduction of lady-birds, and of a certain parasitic fly. It is said that these insects destroyed the "scale" in six months!
Experiments have also been tried with fungi. There are certain fungi which attack the bodies of living insects. So far, however, it cannot be said that the results have been at all satisfactory, for the propagation and infection of the living insects by fungus spores is not at all easy. There is also a certain feeling of doubt as to what may happen. Those fungi, and particularly bacteria, might set up dangerous epidemics.
Decaying meal contains hundreds of certain very curious worms called Nematodes. They are short, about one-twenty-fifth of an inch in length, and are smooth and very like minute eels. These creatures are very active, wriggling or swaying to and fro in a characteristic manner. Now in decaying meal there is a peculiar fungus. Like most fungi, it consists of very minute transparent threads which contain living matter or protoplasm. This particular fungus has branches, but also forms curious loops or belts. When one of these eel-worms is swaying about in the meal, it may quite well happen that its tail slips into one of these loops. If that happens, the fate of the worm is sealed, for the loop is elastic, and the more it wriggles the farther it slips in and the stronger it is held. The fungus then begins to grow, and forms a tube which grows into the worm and kills it. All the material in the worm's body goes to nourish the fungus. This extraordinary fungus has been described and figured by Professor Zopf, but seems to be a very unusual and rare form.
CHAPTER XXIII
THE PERIL OF INSECTS
The Phylloxera—French sport—Life history of the Phylloxera—Cockchafer grubs—Wireworm—The misunderstood crows—Dangerous sucklings of greenflies—"Sweat of heaven" and "Saliva of the stars"—A parasite of a parasite of a parasite—Buds—The apple-blossom weevil—Apple-sucker—The codlin moth and the ripening apple—The pear midge—A careless naturalist and his present of rare eggs—Leaf-miners—Birds without a stain upon their characters—Birds and man—Moats—Dust and mites—The homes of the mites—Buds, insect eggs, and parent birds flourishing together.
THE difficulty in describing the Romance of Plant Life does not arise from a want of romance, but the sieges, battles, and alarms are so difficult to see, and the enemies are so tiny, that the terrific contests continually going on escape our notice altogether.
When one does look carefully and closely at the life of a plant, one sometimes wonders how it manages to exist at all in the midst of so many and great dangers.