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.