CHAPTER V.. Honey-Dew.

HONEY-DEW.

The term +honey-dew+ is applied to those sweet clammy drops that glitter on the foliage of many trees in hot weather. The name of this substance would seem to import, that it is a deposition from the atmosphere, and this has been the generally received opinion respecting it, particularly among the ancients; it is an opinion still prevalent among the husbandmen, who suppose it to fall from the heavens: +Virgil+ speaks of "Aërii mellis cœlestia dona:" and +Pliny+ expresses his doubts, "sive ille est cœli sudor, sive quædam siderum saliva, sive purgantis se aëris succus." The Rev. +Gilbert White+, in his Naturalist's Calendar, regards honey-dew as the effluvia of flowers, evaporated and drawn up into the atmosphere by the heat of the weather, and falling down again in the night with the dews that entangle them. But if this were the case, the fall would be indiscriminate, and we should not have it confined to particular trees and shrubs, nor would it be found upon green-house and other covered plants. Some naturalists have regarded honey-dew as an exudation or secretion from the surface of those leaves upon which it is found, produced by some atmospheric stroke, which has injured their health. +Dr. Darwin+ stands in this class. Others have viewed it as a kind of vegetable perspiration, which the trees emit for their relief in sultry weather; its appearance being never observed in a cold ungenial summer. Dr. +Evans+ is of this opinion, and makes the following comparative remark: "As the glutinous sweat of the negro enables him to bear the fervours of his native clime, far better than the lymph-perspiring European; so the saccharine dew of the orange, and the fragrant gum of the Cretan cistus, may preserve them amidst the heats even of the torrid zone." Mr. +Curtis+ has given it as his opinion that the honey-dew is an excrementitious matter, voided by the aphis or vine-fretter, an insect which he regards as the general cause of what are called blights. He assures us that he never, in a single instance, observed the honey-dew unattended with aphids.

I believe it will be found that there are at least two sorts of honey-dew; the one a secretion from the surface of the leaf, occasioned by one of the causes just alluded to, the other a deposition from the body of the aphis. Sir +J. E. Smith+ observes of the sensible perspiration of plants, that "when watery, it can be considered only as a condensation of their insensible evaporation, perhaps from some sudden change in the atmosphere. Groves of poplar or willow exhibit this phenomenon, even in England, in hot calm weather, when drops of clear water trickle from their leaves, like a slight shower of rain. Sometimes this secretion is of a saccharine nature, as +De la Hire+ observed in orange trees." "It is somewhat glutinous in the tilia or lime-tree, rather resinous in poplars, as well as in Cistus creticus." "Ovid has made an elegant use of the resinous exudations of Lombardy poplars, which he supposes to be the tears of Phaëton's sisters, who were transformed into those trees. Such exudations must be considered as effusions of the peculiar secretions; for it has been observed that manna may be scraped from the leaves of Fraxinus ornus, as well as be procured from its stem by incision. They are often perhaps a sign of unhealthiness in the plant; at least such appears to be the nature of one kind of honey-dew, found in particular upon the beech, which, in consequence of an unfavourable wind, has its leaves often covered with a sweet exudation, similar in flavour to the liquor obtained from its trunk. So likewise the hop, according to +Linnæus+, is affected with the honey-dew, and its flowers are rendered abortive, in consequence of the attacks of the caterpillar of the Ghost moth (Phalæna Humuli) upon its roots. In such case the saccharine exudation must decidedly be of a morbid nature."

The other kind of honey-dew which is derived from the aphis, appears to be the favourite food of ants, and is thus spoken of by Messrs. +Kirby+ and +Spence+, in their late valuable Introduction to Entomology. "The loves of the ants and the aphides have long been celebrated; and that there is a connexion between them you may at any time in the proper season, convince yourself; for you will always find the former very busy on those trees and plants on which the latter abound; and if you examine more closely, you will discover that the object of the ants, in thus attending upon the aphides, is to obtain the saccharine fluid secreted by them, which may well be denominated their milk. This fluid, which is scarcely inferior to honey in sweetness, issues in limpid drops from the abdomen of these insects, not only by the ordinary passage, but also by two setiform tubes placed, one on each side, just above it. Their sucker being inserted in the tender bark, is without intermission employed in absorbing the sap, which, after it has passed through the system, they keep continually discharging by these organs. When no ants attend them, by a certain jerk of the body, which takes place at regular intervals, they ejaculate it to a distance." The power of ejecting the fluid from their bodies, seems to have been wisely instituted to preserve cleanliness in each individual fly, and indeed for the preservation of the whole family; for pressing as they do upon one another, they would otherwise soon be glued together, and rendered incapable of stirring. "When the ants are at hand, watching the moment at which the aphides emit their fluid, they seize and suck it down immediately: this however is the least of their talents; for the ants absolutely possess the art of making the aphides yield it at their pleasure; or in other words of milking them." The ant ascends the tree, says Linnæus, that it may milk its cows the aphides, not kill them. Huber informs us that the liquor is voluntarily given out by the aphis, when solicited by the ant, the latter tapping the aphis gently, but repeatedly with its antennæ, and using the same motions as when caressing its own young. He thinks, when the ants are not at hand to receive it, that the aphis retains the liquor for a longer time, and yields it freely and apparently without the least detriment to itself, for even when it has acquired wings, it shows no disposition to escape. A single aphis supplies many ants with a plentiful meal. The ants occasionally form an establishment for their aphides, constructing a building in a secure place, at a distance from their own city, to which, after fortifying it, they transport those insects, and confine them under a guard, like cows upon a dairy farm, to supply the wants of the metropolis. The aphides are provided with a hollow pointed proboscis, folded under the breast, when the insects are not feeding, with which instrument they puncture the turgid vessels of the leaf, leaf-stalk or bark, and suck with great avidity their contents, which are expelled nearly unchanged, so that however fabulous it may appear, they may literally be said to void a liquid sugar. On looking steadfastly at a group of these insects (Aphides Salicis) while feeding on the bark of the willow, their superior size enables us to perceive some of them elevating their bodies and emitting a transparent substance in the form of a small shower.

"Nor scorn ye now, fond elves, the foliage sear, When the light aphids, arm'd with puny spear. Probe each emulgent vein till bright below Like falling stars, clear drops of nectar glow."

+Evans.+

The willow accommodates the bees in a kind of threefold succession, the farina of the flowers yielding spring food for their young,--the bark giving out propolis for sealing the hives of fresh swarms,--and the leaves shining with honey-dew in the midst of summer scarcity. But to return to the aphides. "These insects may also be seen distinctly, with a strong magnifier, on the leaves of the hazel, lime, &c. but invariably on the inferior surface, piercing the vessels, and expelling the honey-dew from their hinder parts with considerable force." "These might easily have escaped the observation of the earlier philosophers, being usually concealed within the curl of the leaves that are punctured." The drops that are spurted out, unless intercepted by the surrounding foliage, or some other interposing body, fall upon the ground, and the spots may often be observed, for some time, beneath the trees affected with honey-dew, till washed away by the rain. When the leaves of the kidney-bean are affected by honey-dew, their surface assumes the appearance of having been sprinkled with soot.

Honey-dew usually appears upon the leaves, as a viscid, transparent substance, sweet as honey, sometimes in the form of globules, at others resembling a syrup, and is generally most abundant from the middle of June to the middle of July.

It is found chiefly upon the oak, the elm, the maple, the plane, the sycamore, the lime, the hazel and the blackberry; occasionally also on the cherry, currant, and other fruit trees. Sometimes only one species of trees is affected at a time. The oak generally affords the largest quantity. At the season of its greatest abundance, the happy humming noise of the bees may be heard at a considerable distance from the trees, sometimes nearly equalling in loudness the united hum of swarming. Of the plane there are two sorts; the oriental and the occidental, both highly ornamental trees, and much regarded in hot climates for the cooling shade they afford.

"Jamque ministrantem Platanum potantibus umbram."

+Virgil+

The ancients so much respected the former that they used to refresh its roots with wine instead of water, believing, as Sir William Temple has observed, that "this tree loved that liquor, as well as those who used to drink under its shade."

"Crevit et affuso latior umbra mero."

+Virgil+

The sycamore has been discarded from the situation it used formerly to hold, near the mansions of the convivial, owing to the bees crowding to banquet on its profusion of honey-dew, and occasioning an early fall of its leaves. The lime or linden tree has been regarded as doubly acceptable to the bees, on account of its fragrant blossoms and its honey-dewed leaves appearing both together, amidst the oppressive heats of the dog-days; but it seems doubtful whether the flowers have any attraction but their fragrance, as they are said to have no honey-cup.

It is of great importance to apiarians who reside in the vicinity of such trees as are apt to be affected with honey-dew, to keep their bees on the storifying plan, where additional room can at all times be provided for them at pleasure, as during the time of a honey-dew, more honey will be collected in one week than will be afforded by flowers in several. So great is the ardour of the bees on these occasions, and so rapid are their movements, that it is often dangerous to be placed betwixt the hives and the dews.

That species of honey-dew which is secreted from the surface of the leaves, appears to have been first noticed by the +Abbé Boissier de Sauvages+. He observed it upon the old leaves of the holm-oak and upon those of the blackberry, but not upon the young leaves of either; and he remarked at the same time, that neighbouring trees of a different sort were exempt from it: among these latter he noticed the mulberry tree, "which," says he, "is a very particular circumstance, for this juice" (honey-dew) "is a deadly poison to silk-worms."

Some years do not afford any honey-dew, it generally occurs pretty extensively once in four or five years.