(_Danais Archippus._)
The writer was recently examining one of the species of the milk-weed
that is grown in our greenhouses, the _Asclepias Curassavica_, when to
his surprise there were found several of the larvæ of the Archippus
Butterfly feeding upon the leaves. The plants had been taken from the
greenhouse and plunged in a frame for the summer, and the female of this
butterfly, in her wanderings about the grounds in search of milk-weed
plants upon which to deposit her eggs, with a knowledge of botany far
beyond that of many a gardener, had recognized this A. Curassavica as a
species of milk-weed upon which the young larvæ could comfortably feed.
[Illustration: Fig. 11.]
It is very interesting to observe the habits of insects. They seem to be
endowed with some faculties that are not given to animals of a higher
order. By what powers of perception was this butterfly enabled to tell
that this plant, which she had never seen before, that cannot endure our
climate but must be kept in a warm greenhouse, belonged to that genus of
plants which were the proper food of her young? We attain to such
knowledge only by much study and comparison; she sailing past on
careless wing, without having read the first lesson in botany, knows the
foreigner to be a milk-weed, and stops to deposit her eggs upon it, that
when the young larvæ hatch out they may have suitable food at hand.
The eggs she lays are very small, conical objects, about the
twenty-fifth part of an inch long, white at first, but in two or three
days turning yellow, and then just before the time of hatching they
become a dull grey. If one of these eggs is examined with a microscope
it is seen to be covered with a beautiful net-work of raised lines, the
longitudinal lines appearing like ribs joined together by cross lines,
and coming together at the apex. The lower part of the egg, by which it
adheres to one of the leaf-ribs on the under side of the leaf, is
flattened, giving the egg the appearance of a truncated cone, or of one
of those conical bullets, which are used in breech-loading rifles. If
the reader will look at fig. 11, _a_, he will see a magnified
representation of the egg, showing the longitudial ribs and cross lines;
and at _c_, the egg of natural size, attached to the rib on the under
side of the leaf, just as the butterfly places it.
In about a week after the butterfly has deposited the egg, there hatches
from it a very small caterpillar, not more than the tenth of an inch
long. It however grows very rapidly, and soon becomes too large for its
jacket. But its jacket is very accommodating, and when the little fellow
has got tired of it and wants a new one, the old one splits down the
back, so that he can crawl out of it with a new jacket on, and looking
as bright and gay as any new suit. And now it is a very pretty little
creature, with transverse bands of black, yellow, and white, and a pair
of black horns near the head, and another pair not quite so long near
the other end. If it is examined with a microscope a few black hairs
will be seen on each segment; these are shown at _e_ and _f_ in fig. 11.
The caterpillar seems to eat as though eating was the sole purpose of
its life, and in consequence it increases in size very rapidly, so that
it is obliged to crawl out of its skin twice more before it has attained
its full size. This process of changing its coat is called moulting.
Just before each moult it ceases to eat for a few hours, but as soon as
that process is over, it falls-to again with greater voracity than ever.
At each moult the black fleshy horns become longer. The new horns are
nicely folded up under the skin, as can be seen at _d_, fig. 11, but
soon grow straight after the old skin has been cast off.
[Illustration: Fig. 12.]
If any of our readers, the younger readers especially, have a desire to
begin the study of entomology, they will find this insect a very
interesting subject with which to make a beginning. The writer can well
remember his excursions to a neighboring field overgrown with milkweeds,
when he had scarce attained to the dignity of pantaloons, in search of
these beautiful larvæ. These he gathered in considerable numbers,
confined them in a box, and watched with delighted interest the various
metamorphoses they underwent. Those who have never witnessed them, if
they have any taste for the study, will be surprised and greatly
gratified to watch the changes undergone in the progress from the egg to
the butterfly. The creature is of such a size, and so beautiful in all
its stages, that there is no difficulty in seeing it at all times, and
each step adds some new feature of interest.
When the caterpillar has attained its full size it will be about an inch
and three quarters in length, and will have the appearance shown in fig.
12. The markings are very distinct. Each segment has a transverse band
of black in the centre, bordered on each side with white, with a yellow
band between. After it has reached this stage of its life it ceases to
eat, and presently begins to roam about in search of a suitable place to
undergo its next change. And a wonderful change it is; instead of a
hungry creeping creature, eating voraciously night and day, it is about
to fasten itself to a spot from which it can not move, and pass into a
condition in which it will have neither mouth to eat with, nor feet with
which to walk. To all outward seeming it will have ceased to live; cold,
and stiff, and motionless, it will manifest no sense of feeling
whatever, nor any symptom of life.
Having found a place suitable for the metamorphose about to take place,
which will always be the underside of some convenient support, the
caterpillar proceeds to cover a considerable space, a diameter of three
or four inches, with fine, white, silken threads, which it spins from
its mouth, or from spinnarets placed at the mouth. These silken threads
are laid on thicker and thicker towards the centre of the chosen spot,
and at the centre a small pointed knob is raised of the same material.
All this is done in order that the creature may suspend itself, head
downwards, and hang securely by this silken knob without danger of being
torn by its weight from its fastenings. Having completed all these
arrangements, it proceeds to suspend itself by fastening the hooks on
the pair of feet upon the last or anal segment into the silken knob, and
when these are secured lets go its hold of the silken carpet with all
the other feet and hangs suspended in mid-air, from the underside of
some fence rail, or horizontal bar, or if in confinement, from the lid
of the box or ceiling of the room.
What strange spell is upon the creature that it leaves its food, which a
short time ago was all its desire, and travels off in search of some
hidden retreat, some lonely nook? And why is it now travelling round and
round within the circumference of a few inches upon the ceiling, laying
down so carefully such a network of silken threads? Who has told it to
lay them down increasing in thickness from the circumference to the
centre? And now it has ceased to travel about, and has stationed itself
with its head in the centre of its silken carpet; if you will watch it
closely, you will see that it is yet spinning, and now and then it moves
its head to the right and left, about as far as it can conveniently
reach. As you look you see a little projection is being built up
directly under its head, and that these motions to the right and left
are made in the act of laying down some anchoring cables that shall
fasten it securely to the web or carpet it has fastened upon the
ceiling. What schoolmaster taught it that a cone is the strongest form
in which it can arrange its gossamer threads? And who told it to go and
hang itself thereby, suspended from its hindermost feet? Does it know
the future that is before it; the life that lies beyond this gateway of
seeming death? (_Continued in next No._)
[Illustration: The Canadian Horticulturist]
=VOL. I.]= =OCTOBER, 1878.= =[NO. 10.=