Meddle not with him that flattereth with his lips.
On keeping away people we don’t want
Not all insects are welcome visitors to plants; there are unbidden guests who do harm. To their visits there are often obstacles. Stiff hairs, impassably slippery or viscid stems, moats in which the intruders drown, and other structural peculiarities, whose origin may have had no reference to insects, often justify themselves by saving the plant. Even more interesting, however, is the preservation of some acacias and other shrubs by a bodyguard of ants, which, innocent themselves, ward off the attacks of the deadly leaf-cutters. In some cases the bodyguard has become almost hereditarily accustomed to the plants, and the plants to them, for they are found in constant companionship, and the plants exhibit structures which look almost as if they had been made as shelters for the ants. On some of our European trees similar little homes or domatia constantly occur, and shelter small insects, which do no harm to the trees, but cleanse them from injurious fungi. (J. Arthur Thomson, M. A.)