Article beginning on page 351.
Psyche 7:351-361, 1894.

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THE HIBERNATION OF APHIDES.
BY CLARENCE M. WEED, DURHAM, N. 11.
[Annual address of the retiring president of the Cambridge Entomological Club, 14 febraary, 1896.1 In latitudes where winter is a period
of protracted cold, a successful mode of passing through it is of fit s1 importance to all animals hat cannot follow the
swallow with the changing season.
Such creatures must not only endure
the low temperatures 1.0 which they :we
subjected, but also must so protect them- selves thai a cei tain proportion of them, at least, bh:dl escape the attacks of the various enemies that are h+o:irl during' this long period of forced inactivity.
With insects successful hibernation is
of vital importance, and each species
appears to have chosen (largely 1111 niigli the action of iiatural selection) i!ic safest method of passing thro'ugh. A vast
number of them hibernate in the egg
state; many in the larva! state ; many
as pupae; and a considerable propor-
tion as adults. Not infrcqiicntiy the
same species may hibernate in two or
more of these conditions.
In such cases
it is evident that if the insect in one
stage suffers more loss than in the other. the latter - other things being equal -
will gradually replace the former as the hibernating condition.
The aphides furnish an interesting
illustration of the various metliods the different species of a single family may :idopt to pass the winter. The normal
life-history of these little creatures may be briefly summarized as follows. In
the spring there hatches from an egg
deposited the autumn previous, a little
aphid that sucks the sap of its food
plant for a number of clays - sometimes
a fortnight -before it becomes full-
grown. During' this period of growth,
i~ molts or sheds its skin a number of
times to provide for its rapidly increas- ing size. This insect is sometimes
called the stem-mother. She is always
wingless. Soon after reaching nxiturity
she commences to give birth to living
young, continuing the process usually
for several days. These young are
most con~monly born naked, but hi
some species they are surrounded lyy a
thin pcllicle which ruptures soon after
birth. They resemble the stem-mother
in general appearance, being of course
much smaller. Each soon begins suck-
ing sap on her ow11 account, and in the
course of ten days or a fortnight becomes mature. It then begins bringing other
aphides into the world: these soon
mature and give birth to a third germ=
ation. All of the individuals of these
early broods are parthenogenetic females giving birth to living young without the



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352 PSYCHS. [March 1896.
presence of males.
Many of them are
provided with wings but the majority
are wingless. This n~et:hod of repro-
duction is continued throughout the
warm season, but on the approach of
cold weather a true sexual generation is produced, the males of which may be
cither winged or wingless while the
females are always wingless. Sexual
union between these two forms takes
place, and the females deposit true eggs. These pass throiig11 the winter, and in
spring hatch into stem-mothers which
renew the cycle of existence.
The great majority of aphides pass
through the winter in the egg state.
This is doubtless the safest way, for
even supposing the viviparous or sexed
forms capable of enduring intense cold,
they wo~~ld be much more liable to be
eaten by birds, scattered by winds or
washed away by floods, than the eggs.
The latter are nearly always at least
partially secured against these vicissi- tudes, although doubtless millions of
them perish from exposure to the
elements, or are gobbled up by the
hungry beaks of chickadees and other
winter birds. But as a rule the eggs
are so small and so carefully stowed
away, that a sufficient number to propa- gate the species survive all perils.
Perhaps as simple a method of pro-
viding for the eggs as any is that
adopted by a handsome yellow Callip-
terus (C. discolor Monell) which I
studied in Illinois a few years ago.
This species lives on the under side of
oak leaves, particularly the Burr Oak
(~ZLWCZLS macrocar&z) generally on
limited colonies. In autumn a sexed
generation is produced, the males
having wings and Hie oviparous
females being provided with a long,
tapering ovipositor by means of whicli
they push the eggs through the dense
pubescence on the under side of the
leaf, gencrdly fastening it firmly
against the mid-rib. Many of these
leaves remain on the tree until quite
late in spring; and it is fair to pre-
sume that a sufficient proportion of the aphides hatch before the leaves fall
off, climb upon the twigs and begin
sucking at the buds, although this lias
not so far as I know been observed.
The eggs are certainly safer hidden
in the pubescence of the leaves, from
observation by birds, than they would
be upon the twigs.
Frum fastening the egg to the leaf to
attaching it to the bark of the twig
is a short step, and one which appears
to have been taken by a majority of the
aphides affecting trees and shrubs. In
many cases it has ~iaturally resulted
from the insects being compelled to
migrate to the twigs by the early falling of the leaves. In many of the states in
the valleys of the Mississippi and its
tributaries where the Box Elder or Ash-
leaved Maple (Negundo aceroides) is
abundant, its foliage is often infested by a small aphid of the genus Chaitophorns
(C. negundoides). In autumn the
sexed forms leave the falling leaves and congregate in great numbers 'on the
twigs. The males are wingless little
creatures with slender flattened bodies, barely two millimeters in length, and




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March 1396.1 PSYCHE. 353
long legs and antennae. The egg-lay-
ing females arc larger and have much
broader bodies. They deposit their
eggs irregularly upon the bark of the
twigs, especially about the buds. The
eggs are elliptical-ovoid, less tlian one nlimcter long, greenish or yellowish
brown when first laid, but graclnally
changing to shining black.
There is a pretty little aphis (A.
enonymi} living' upon the under surface
of the leaves of the shrub called Burn-
ing Bush (Enonymus atropz~rpzweus).
In autumn the oviparous females con-
greg'iite on the twigs and deposit their eggs in the crevices about the buds.
A curious little Callipterns which
I found commonly on the leaves
of Beech in centrill Ohio a few years
;go also repairs to the bark for ovipo-
sition, but is much more careful in
concealing the eggs. The viviparous
colonies are found late in summer and
early in autumn on the under sides of
the leaves, with more or less flocculcnl inattei" about them. The sexed ~OI-I~S
develop during October, and the ovi-
parous females wander over the bark of
the twig's, limbs, and tmnk, in search
of crevices in which to deposit their
eggs. When a suitable place is found
the egg is laid, and is then driven into position by the following method. The
insect so places hcrsclf that her liind
Iep easily touch the egg ; then standing on her four front legs, she brings the
two hind ones down upon the egg in
rapid succession, striking with eonsid-
erable force. This serves Llie double
purpose of pushing the egg" into place,
and of dr.-iwing out -A viscid secretion with which it is covered into a tlircad- like silvery film so similar to the sur- rounding bark that it is difficult to
detect the difference. A minute and a
hi11S to two miniit~'~ are spent in this process.
Recent observations have shown that
a number of species of aphides live upon various trees c1n1-ingaauturnn, winter,
m i l spring, but for the summer season
migrate to more succulent herbaceous
plants. The best authenticated exam-
ple of this is the Hop Aphis (Phorodon
humidi) which was carefully studied
both in Europe and America by Dr.
C. V. Riley. The life-history of the
species is briefly this. The insect passes the winter in the egg st:ite on plum
trees. In spring- each egg hatches into
a small aphid that sucks the sap from
the expanding leaves. This is the so-
callcd stem-mother. She becomes full-
Town in a week or two and then begins
bringingforth living young ;it an average rate of about three each clay, continuing the process until she has becrtine the
mother of a hundred or more rapidly
developing aphides. Each of these in
turn gives birth to other young in the
same way. Three generations of these
pnrthenogenetic forms are produced
npon the plnm, the last becoinin:
winged and deserting the trees to seaicli for hop plants. On finding them these
winged migrants light upon the under
aides of the leaves where they start
colonies; and the species continues
developing upon the hop plant through-
out the summer. In early autumn an-




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354 t'S TCHE. [~a~ch IS^^.
other winged generation is produced,
which migrates back to the plum (on
which account these forms are some-
times called return-migrants), where
each settles upon a leaf and gives birth to three or more young that develop into sexual oviparous females. About the
WdmC time winged males are produced
upon the hops. They also migrate to
the plum "where they mate with the
oviparous females. The latter deposit
the winter eggs upon the twigs about
the buds; and on the advent of cold
weather all forms but the eggs perish.
There is no doubt thai a considerable
immber of the aphides commonly aEect-
inn- irecs and shrubs have a somewhat
a
similar history.
Fur instance our com-
mon apple aphis (A. ma&) spends the
summer upm grasses, where they con-
tinue breeding until autumn, when they
return to the apple, and the winged
females establish colonies of the wing-
less egg-laying form upon the lcavcs.
The males fly in from the s~~mmei-
host-plant. The eggs are then laid on
the twigs and buds zind the cycle for the year is completed.
The aphid commonly affecting
cherry trees (Afyszts cerast} has a
similar history. It winters over on
the twig's in the egg state. Early in
spring the young aphidcs hatch and
crawl upon the bursting buds, insert-
ing their tiny sap-sucking beaks into
the tissues of the unfolding leaves.
In a week or ten days they become
full-grown and begin giving birth to
young lice, which also soon develop
and repeat the process, increasing
very rapidly.
Most of the eaily spring
forms are wingless but during' June
great numbers of tlic winged lice
appear, and late in June or early in
July they generally leave the cherry,
migrating to some other plant, although
we do not yet know wliat that plani
is. Here they continue clevelopinp
throughout the summer, and in autumn
a winged brood again appears and
migrates back to cherry. These
migrants give birth to young that
develop into egg-laying females which
deposit small, oval, shining black eggs
upon the twigs.
While the aphides allecting decidu-
OLIS trees commonly live upon the
leaves ~1x1 deposit eggs upon the buds.
the rule is reversed in. the case of
some species found upon conifers. For
instance the large Lachnus (7;. $a)
occurring upon the twigs of Scotcli
Pine deposits eggs in longitudinal
rows upon the leaves. The handsome
White Pine I~acl~nus (L. sirobi} has
also a similar habit. Like most plant-
lice. this species reproduces vivipa-
rously, or by giving birth to living-
young, during the summer, but on
the approach of cold weather the
sexual individuals are produced. Dur-
ing October these are usually the
only forms present, tlie oviparous
females being congregated in great.
numbers upon the bark of the smaller
branches, with their heads directed
towards the trunk of the tree. When
disturbed they move about rapidly,
usually attempting to conceal them-
selves on the other side of the branch.




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March i8q6.1 f's2xxI7. 3%
At such times they also wave their
long hind legs in the air, probably to
flighten away predaceous or parasitic
enemies. The males are winged and
the oviparous females wingless. The
eggs are deposited in longitudinal
rows on the White Pine leaflets.
Each egg is not quite one-tenth of
an inch Ions elongate-oval, brownish
when first extruded but soon chang-
ing to shining black.
Besides the aphides liv-
. ing upon leaves and ovi-
positing upon twigs, and
those living- iipon twigs
and ovipositing upon
leaves, there are many
species which both live
and oviposit upon the
twigs. Seven11 such forms
occur upon willow, the
prettiest one being the
Spotted Willow Aphis
(Melanoxanthns salicis).
This insect lives over win-
ter in the egg slate on
the hark of willow twiss.
suminer they have often increased so
enormously as to cover all the twigs
of infested trees. making them appear
filthy tind unsightly, as well as impair- ing their vitality by extracting the sap. In auliimn a sexed generation is pro-
duced. the males of which may be
either winged or wingless. In Ohio
I have found only winged males, while
in New Hampshire I found both forms,
the apterous ones being much the more
F. Uetmrrs. del.
b
Fig. I.
Floi-eulent Willow Aphis: a, oviparous female-enlarged; b, head and antennae of same-greatly enlarged; c, eggs on willow bark-one-half larger than natural sizes.
-
Early in spring the eggs
hatch into young plant-lice which insert their tiny beaks into the tender bark and suck out the sap. Thcy grow rapidly,
and each one soon becomes the motliei
of several young aphides.
The genera-
tion from the egg are all wingless, but
those of the second generation probably
develop into both winged and wingless
forms, which are also viviparous. Snc-
cessive broods continue to appeal
throughout the entire summer, all being
viviparous, and some having wings
while others have none. By mid-
abundant. The oviparous feimies con-
gregate in one or a few places for pur-
poses of oviposition. In such situations tlicy often cover the liark with their
eggs. When first laid each egg is
coated with a sticky liquid that dries
into a thin, grayish, irregular covering, closely rcscinbling the willow bark in
appearance.
Another species, closely resembling
the spotted one, and called the Floccu-
lent Willow Aphis (M. flocczilosus)
lives upon the Gray Willow in floccu-




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lent colonies, so closely resembling the bark that they are difficult to detect.
The males of this species are wingless.
The ovipai-ous females seem to take
more care than do the spotted ones in
depositing their eggs in the crcvices of rough bark where the peculiar whitish
covering of each helps greatly to con-
ceal it.
There tire two other aphides of the
genus Melanoxanth~~s which live upon
willow twigs but differ from those men-
tioned above in habits of oviposition.
The Bicolored Melanoxantlius (M ti-
color) is a rather rare species found in many of the western States. The males
are winged, and the yellowish brown
oviparous females deposit their eggs in
the crevices about the buds: the latter
after a short exposure to the air become shiiiing" black with none of the flocc~l- lent covering found on the eggs of the
oilier species. The most abundant
member of the genus is that sometimes
called the Willow Grove Aphis (116
salicti) which is similar to the spotted form, but without the conspicuous
white spots. It lives in large colonies
on the twigs and branches. The winged
males and oviparous females dcvelop
in autumn, and the latter oviposit on
the twig's about the buds.
One of the largest aphides living
upon twigs is the Sycamore Laclinns
(L. platam'coh) which occasionally
becomes extremely abundant in many
sections of the United States. The
sexed forms appear early in autumn,
and eggs are deposited in enormous
numbers upon the bark.
Some of the aphides affecting" herba-
ceous plants complete their yearly cycle upon them. The larp'c reddish brown
species (flectaro'phora ~udbeckiae) so
commonly found upon composite plants
of the genus Solidago and Lactuca is
one of these.
In studying its autumn
history in. Illinois a few years ;ip, 1
found that the sexed forms developed
during October, the males having
wings. Eggs were occasionally clepos-
ited upon the okl slems of wild lettuce
(Lactaco candense), but much more
commonly upon the under leaf surface
of the young, first-year plants of Lac-
tuca and the closely allied Muhlen-
bergia. Evidently the chances of sur-
vival and future development are better
in the case of the eggs deposited upon
the leaves of young biennials or peren-
nials, than of those fastened to the old stems which arc liable to be broken off
and blown or washed away, so t111it if
the eggs survived the young aphides
would not be likely to find suitable food at htiucl. [u such cases a system of
natural elimination must tend toward
the preservation of the forms oviposit-
ing- upon the young" plants.
Perhaps the most remarkable fact
coiin~cled with the hibernation of
aphides is that of the preservation of
the eggs through the winter in the
nests of ants. This was discovered
long ago by Huber. and has since been
abundantly confirmed by Schmarda,
Lubbock and others. Huber's account
is so interesting, and apparently so
little known, that I quote it at some