REPRODUCTION AND METAMORPHOSIS
Like their relatives the bees and wasps, ants have developed two
types of females, so that a colony contains three distinct sorts of
individuals, known as males, females, and workers.
_The Male._ The male is less subject to variation than either the queen
or the worker. The body is usually slender and graceful, the eyes and
antennae are well developed, and the mouth parts rather small and weak.
In most species the male is winged. As in the bees, the one great
function of the male in the colony is to copulate with the female or
queen, so as to supply her with sperm to fertilize future eggs. The
male is not killed in the course of the sexual embrace, as the drone
honeybee is, but usually dies soon afterward.
_The Female._ The true female or queen is usually larger than either
the male or the worker; the head, eyes, and mandibles are well
developed, and the abdomen is very large to contain the reproductive
organs. The female is usually winged at the time of mating, but the
wings are loosely attached and she loses them as soon as the nuptial
flight is over. The wings and legs are stouter and shorter than those
of the male, in most cases. In a few species the females have no wings,
and in others it is the males which are wingless. No case is known in
which neither male nor female is provided with wings.
_The Worker._ The worker is an undeveloped, wingless female. The eyes
are small, and the ocelli are often lacking; the antennae, legs, and
mouth parts are strong and well developed. There is a great deal
of variation among workers; one common variant is the _dinergate_,
or soldier--a form with a very large head and mandibles adapted to
fighting. The sex organs of the worker are unquestionably female, but
they do not ordinarily function, and a worker has never been seen to
copulate.
_Mating._ In species in which both the male and female are winged,
mating occurs in the air, as in the nuptial flight of the queen bee. In
the case of the honeybee, however, there is only one queen to a great
number of drones, while with the ants there may be hundreds of queens
and drones in the air, all copulating at once. Another difference is
that the mated females do not often return to the parent colony, as the
queen bee always does. When the mating hour draws near all the ants,
even the nearly blind and wingless workers, rush out of the nest in
great excitement, and the air is soon full of flying ants. Copulation
usually begins high in the air, but the linked pairs often fall to
the ground together. In the mating of bees the male is almost always
instantly killed, the genital organs and entrails being torn out of
his body. This mutilation never happens among ants, but the male’s
life-work is ended with the sexual act, and he usually dies shortly
afterward.
_The New Colony._ As soon as the mated female is upon solid ground
again she tears off her wings, or removes them by rubbing against
some solid object. This done, condemned to a crawling, terrestrial
existence for the rest of her days, she sets out alone to establish
a new colony. She digs a hole in the ground, or in rotten wood, or
under a flat stone, seals up the opening, and sits down in the dark
until the eggs in her abdomen are mature. Sometimes this takes weeks
or even months, and during this time the queen has nothing to eat,
but lives by absorbing the large wing-muscles which she will never
use again. Finally the eggs are deposited, being fertilized by some
of the spermatozoa which were obtained from the male, and which are
stored in the spermatheca, a little pouch just above the uterus. When
the larvae hatch she feeds them with a secretion from her salivary
glands. The resulting ants are normal workers, except that they are
unusually small. Sometimes it takes nearly a year to rear this first
brood, and all this time the queen has eaten absolutely nothing. As
soon as the workers are old enough they dig passages to the open air,
and enlarge the nest by adding galleries and runways. They drag in
food and feed the exhausted female, who from this time forward does
nothing but eat and lay eggs--the brood being cared for entirely by the
workers. From now on the female is a timid, photophobic, rickety old
egg-laying machine. During her long fast the great wing-muscles have
been absorbed, leaving the thorax hollow, so that she floats if placed
in water. Only a very few females can survive the ordeal necessary to
found a new colony--probably only one of many thousands which undertake
it. It is a beautiful example of the Darwinian phenomena of survival.
The procedure described above is the usual one in most species of
ants. It was guessed at by Huber in 1810, but the first man to watch
the actual founding of a new colony was an American named Lincecum,
about 1866. In 1879 Sir John Lubbock observed the whole process in an
artificial nest, and his account of the process has since been verified
by numerous other investigators.
In certain species, however, the queen is unequal to the task of
founding a family in this manner. In this case she must return to the
parent colony, join a queenless colony of her own or an allied species,
or raid a small colony of aliens. In this latter event she kills them
all, and adopts their eggs and brood.
_Complete Metamorphosis._ Like the butterflies and beetles, ants have
a complete metamorphosis, that is, they pass through four distinct
developmental stages. In many other insects--the grasshoppers for
example--the metamorphosis is said to be incomplete, because the newly
hatched young have the same general form as the adult, and their
development is merely a matter of increase in bulk.
_The Egg._ Ant’s eggs are very small, rarely more than one-fiftieth of
an inch in length, and are very seldom seen by the casual observer, who
mistakes the comparatively large cocoons for eggs. The egg is usually
elongated, and consists of the germinal spot, the yolk, and the thin
transparent shell called the chorion. The eggs look very much alike,
and one cannot predict whether a given egg will produce a male, a
worker, or a queen. Some eggs are fertilized by sperm stored in the
female’s spermatheca, others are deposited without fertilization, while
those laid by workers are certainly not fertilized, since workers do
not copulate. In bees and certain other related insects it has been
found that unfertilized eggs always produce males, but whether this is
always true in ants is still an open question.
Very little is known of the embryological development of the ant, but
the unhatched larva certainly has traces not only of antennae and legs,
but remnants of certain abdominal appendages not present in the adult
ant, and evidently harking back to more remote ancestors. The egg
usually hatches about twenty days after it is laid, but the length of
this period varies greatly with the temperature.
_The Larva._ The newly hatched larva is a soft, semi-transparent grub,
with a fat body, slender crooked neck and small head. There are no
eyes, but the mouth-parts are fairly well developed, and ten pairs of
stigmata are usually present. The body is covered with short fine
hairs. The digestive system is well formed, but there is no connection
between the stomach and the intestine, so that the larva has no
movement of the bowels until it is about to transform into the next
stage. The accumulated feces in the lower part of the stomach may often
be seen as a black spot showing through the semi-transparent walls of
the body.
[Illustration: Fig. II. Cross-section of an ant-hill, showing the
arrangement of larvae and pupae according to size. (Adapted from
Andre.)]
The larva is fed by the workers, the food being either regurgitated
liquid food or pieces of fresh vegetable or animal matter. It has been
found in the case of the bees that the kind of food given the larva
determines whether it will develop into a queen or a worker, but we
have no definite information about this matter among the ants.
When the larva is fully grown, usually about a month after hatching, it
is buried in the ground by the workers, and spins a silken cocoon about
itself. All ant larvae have spinning organs in the head, but some do
not spin cocoons, and in this case are not buried, but undergo their
metamorphosis in the open chambers of the nest. The larva now voids its
accumulated feces, sheds the larval skin, and appears as the pupa, the
third stage in the ant’s development.
_The Pupa._ In the pupal stage the ant has most of the appendages and
organs of the adult, but they are small and folded close against the
body. The pupa lies quietly, is not fed, and ordinarily gives no signs
of life at all. Gradually the various parts develop, the darker color
of the adult appears, until finally the mature pupa has very much the
appearance of the imago. Then the cocoon is opened by the attendant
workers, the young ant dragged out and fed, and begins its life as an
adult. The pale, newly emerged ant is known as a _callow_. The pupal
stage usually lasts from fifteen to twenty days, but is sometimes much
longer in cold weather.
_The Adult._ The general appearance and characteristics of the adult
are described elsewhere in this book. The total time of development
from the deposition of the egg to the appearance of the callow varies
from about sixty days to five months, and is considerably longer than
the corresponding period in most other insects. The queen bee, for
example, passes through all three stages in about sixteen days, while
some butterflies are developed in less than twenty-five days. Another
interesting feature is the extreme longevity of the adult ant. The
males are short-lived, but the workers of many species live for four
or five years, and the queens for still longer periods. Janet kept one
for fully ten years, and Sir John Lubbock had a queen in his possession
from December, 1874 to August, 1888, “when she must have been nearly
fifteen years old, and, of course, may have been more,” since he had no
means of knowing her age at the beginning of her captivity.