It is quite common to find ants crawling about on the outside of the large heads of the Garden Centaury and a few other Composites. If one looks carefully, one finds that there are streaks of honey to be seen coming from the scales. The honey is not produced in the flowers, and seems at first sight to be of no use at all so far as the plant is concerned, but that is very far from being the case. Here comes a cockchafer or other destructive beetle, intent on absolutely devouring and destroying the young flowers. At once the pugnacity and wrath of the ants are aroused. They take up a menacing and ferocious attitude, and the cockchafer passes to some other plant.[131] [131] Kerner, _l.c._, vol. 2, fig. 264, p. 242. 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.