the insect easily pierces the bark or leaf, and sucks out the sap of the plant tissues. The jointed sheath permits of a change of position without the removal of the beak. A part of the sap is digested, and is used for growth and the production of young, while the residue is expelled as a waste substance known as honey-dew. It is thus undoubtedly an excretion which escapes by way of the anal opening. It may not, however, consist entirely of the waste products of digestion. MacGillivray states that in plant-lice, which produce honey-dew abundantly, the posterior portion of rectum is greatly enlarged and is lined with large active cells which may excrete the honey-dew. The objection to honey-dew on the ground that it is an excretion rather than a secretion is largely imaginary, as secretion is the more general term including excretion.
The quality of honey-dew varies greatly according to the plant on which it occurs and the insects producing it. When freshly gathered it may be clear, sweet, and agreeable in flavor, or at least not unpalatable. The better grades find a ready sale to bakers, who prefer it for baking purposes to floral honey. But usually it is very inferior in quality; for when it remains for days on the foliage it gathers many impurities. A black smut often covers the leaves so that the extracted honey-dew is inky black, resembling tar. This type might, perhaps, be used by manufacturers of blacking or of lubricants. It is not a safe food on which to winter bees. If they are left on the summer stands, and can obtain frequent flights, they may winter in fair condition; but if they are placed in a cellar they will all probably perish from dysentery. For brood-rearing in the spring it is unobjectionable, and it is, therefore, advised that it be removed from the hives in the fall, and sugar syrup fed in its stead.
The composition of honey-dew honeys as compared with floral honeys is shown in the chemical analyses given in the following table:
|Floral honeys —||Water.||Invert sugar||Sucrose.||Ash||Dextrine.||Undetermined.||Free acid as formic.|
|Honey-dew honeys —|
|Hawaiian sugar cane||15.46||64.84||5.27||1.29||10.01||3.13||0.15|
From the above table it is apparent that honey-dew honey contains less invert sugar, but more sucrose or cane sugar, dextrine or gums, and ash, than floral honey. It is because of the larger percentage of gums and ash that it is unsuitable for winter feeding. Honey-dew honey may also be distinguished from floral honey by means of the polariscope. A ray of light passed through a solution of floral honey is turned or rotated to the left; but passed through a solution of honey-dew honey it is turned to the right. If floral honey turns the ray to the right it has been adulterated with glucose. No floral honey is obtained from the wind-pollinated flowers of hickory and white oak.
Besides bees, honey-dew is attractive to wasps, ants, flies, and other insects. Bees pay no attention to plant-lice; but ants care for them and stroke them gently with their antennae in order to induce them to yield honey-dew more freely. This behavior led the botanist Linnaeus to call Aphis the cow of the ants (Aphis formicarum vacca). Ants defend plant-lice from their enemies, move them to new pastures, care for their eggs, and build over them covers of earth, or cow-sheds, to keep them warm. Ants also extend their protection to scale-insects. It has been shown by observation and experiment that plant-lice and coccids which receive the care