long-forgotten years between the Glacial period and the expedition of
Lewis and Clarke were not without interest in the history of the
trout. For all these years the fishes have been trying to mount the
waterfalls in order to ascend to the plateau above. Year after year,
as the spawning-time came on, they leaped against the falls of the
Gardiner, the Gibbon, and the Firehole Rivers, but only to fall back
impotent in the pools at their bases. But the mightiest cataract of
all, the great falls of the Yellowstone, they finally conquered, and
in this way it was done: not by the trout of the Yellowstone River,
but by their brothers on the other side of the Divide. These followed
up the Columbia to the head-waters of the Snake River, its great
tributary, past the beautiful Heart Lake, and then on to the stream
now called Pacific Creek, which rises on the very crest of the
Divide. In the space between this stream, which flows west to help
form the Snake River, and a smaller stream now called Atlantic Creek,
flowing down the east slope of the Divide, the great chain of the
Rocky Mountains shrinks to a narrow plateau of damp meadow, not a
fourth of a mile in width; and some years, when the snows are heavy
and melt late in the spring, this whole region is covered with
standing water. The trout had bided their time until they found it so,
and now they were ready for action. Before the water was drained they
had crossed the Divide and were descending on the Atlantic side toward
the Yellowstone Lake. As the days went by, this colony of bold trout
spirits grew and multiplied and filled the waters of the great clear
lake, where their descendants remain to this day. And no other
fishes--not the chub, nor the sucker, nor the white-fish, nor the
minnow, nor the blob--had ever climbed Pacific Creek. None of them
were able to follow where the trout had gone, and none of them have
ever been seen in the Yellowstone Lake. What the trout had done in
this lake--their victories and defeats, their struggles with the bears
and pelicans, and with the terrible worm, joint enemy of trout and
pelicans alike--must be left for another story.
[Illustration: TROUT.]
So the trout climbed the Yellowstone Falls by way of the back
staircase. For all we know, they have gone down it on the other side.
And in a similar way, by stealing over from Blacktail Deer Creek, they
overcame the Undine Falls in Lava Creek and passed its steep obsidian
walls, which not all the fishes in the world could climb.
In the Gibbon River the cataracts have proved to the trout an
impassible barrier; but, strangely enough, its despised associate, the
sluggish, chunky blob, the little soft-bodied, smooth, black
tadpole-like fellow, with twinkling eyes and a voracious appetite--a
fish who cannot leap at all--has crossed this barrier. Hundreds of
blob live under the stones in the upper reaches of the stream, the
only fish in the Gibbon waters. There he is, and it is a standing
puzzle even to himself to know how he got there. We might imagine,
perhaps, that some far-off ancestor, some ancient Queen of the Blobs,
was seized by an osprey and carried away in the air. Perhaps an eagle
was watching and forced the osprey to give up its prey. Perhaps in the
struggle the blob escaped, falling into the river above the falls, to
form the beginning of the future colony. At any rate, there is the
great impassable waterfall, the blob above it and below. The osprey
has its nest on a broken pine tree, above the cataract, and its tyrant
master, the bald eagle, watches it from a still higher crag whenever
it goes fishing.
Two years ago the Hon. Marshall McDonald, whose duty as United States
Fish Commissioner it is to look after the fishes wherever they may be,
sent me to this country to see what could be done for his wards. It
was a proud day when I set out from Mammoth Hot Springs astride a
black cayuse, or Indian pony, which answered to the name of Jump,
followed by a long train of sixteen other cayuses of every variety of
color and character, the most notable of all being a white pony called
Tinker. At some remote and unidentified period of her life she had
bucked and killed a tradesman who bestrode her against her will, and
thereby, as in the old Norse legends, she has inherited his strength,
his wickedness, and his name. And when, after many adventures, I came
back from this strange land and told the story of its fishes other men
were sent out from Washington with nets and buckets. They gathered up
the trout and carried them to the rivers above the falls, and now all
the brooks and pools of the old lava-bed, the fairest streams in the
world, are full of their natural inhabitants.
[Illustration]
THE COLORS OF ANIMALS
(FROM CHAPTERS IN POPULAR NATURAL HISTORY.)
BY SIR JOHN LUBBOCK, BART., M.P., F.B.S., ETC.
[Illustration]
The color of animals is by no means a matter of chance; it depends on
many considerations, but in the majority of cases tends to protect the
animal from danger by rendering it less conspicuous. Perhaps it may be
said that if coloring is mainly protective, there ought to be but few
brightly colored animals. There are, however, not a few cases in which
vivid colors are themselves protective. The kingfisher itself, though
so brightly colored, is by no means easy to see. The blue harmonizes
with the water, and the bird as it darts along the stream looks almost
like a flash of sunlight; besides which, protection is not the only
consideration. Let us now consider the prevalent colors of animals and
see how far they support the rule.
Desert animals are generally the color of the desert. Thus, for
instance, the lion, the antelope, and the wild ass are all
sand-colored. "Indeed," says Canon Tristram, "in the desert, where
neither trees, brushwood, nor even undulation of the surface afford
the slightest protection to its foes, a modification of color which
shall be assimilated to that of the surrounding country is absolutely
necessary. Hence, without exception, the upper plumage of every bird,
whether lark, chat, sylvain, or sand grouse, and also the fur of all
the smaller mammals and the skin of all the snakes and lizards, is of
one uniform sand color."
It is interesting to note that, while the lion is sand-colored like
the desert, the long, upright, yellow stripes of the tiger make it
very difficult to see the animal among the long dry grasses of the
Indian jungles in which it lives. The leopard, again, and other tree
cats are generally marked with spots which resemble gleams of light
glancing through the leaves.
The colors of birds are in many cases perhaps connected with the
position and mode of construction of their nests. Thus, we know that
hen birds are generally less brightly colored than the cocks, and this
is partly, perhaps, because bright colors would be a danger to the
hens while sitting on their eggs. When the nest is placed underground
or in the hole of a tree, etc., we find it no longer to be such an
invariable rule that the hen bird is dull-colored; but, on the
contrary, she is then often as gaily colored as the male. Such, for
instance, is the case with the hen kingfisher, which is one of the
brightest of British birds and one of the very few which make their
nests underground; the hen woodpecker, which is also gaily colored and
builds in hollow trees, forms a second instance.
In the few cases where the hens are as conspicuously colored as the
cocks, and yet the nest is open to view, we generally find that the
hens are strong, pugnacious birds, and well able to defend themselves.
There are even instances, though these are comparatively rare, in
which the hens are more brilliantly colored than the cocks; and it is
an interesting fact that it is then the cocks, and not the hens, which
hatch the eggs.
It therefore seems to be a rule, with very few exceptions, that when
both the cocks and hens are of strikingly gay or conspicuous colors,
the nest is such as to conceal the sitting bird; while, whenever there
is a striking contrast of colors, the nest is open and the sitting
bird exposed to view.
Again, most fishes are dark above and pale below. This points to the
same fact, for when one looks down into the dark water, the dark color
of their backs renders them the less easy to distinguish; while, to an
enemy looking up from below, the pale belly would be less conspicuous
against the light of the sky. Those fishes which live deep down in the
depths of the ocean present no such contrast between the upper and
under surface. Many of the smaller animals which live in the sea are
as transparent as glass, and are consequently very difficult to
distinguish.
It is sometimes said that if animals were really colored with
reference to concealment, sheep would be green, like grass. This,
however, is quite a mistake. If they were green they would really be
more easy to see. In the gray of the morning and the evening twilight,
just the time when wild animals generally feed, gray and stone colors
are most difficult to distinguish. Sheep were originally mountain
animals, and every one who has ever been on a mountain-side knows how
difficult it is to distinguish a sheep, at some distance, from a mass
of stone or rock.
It is, again, a great advantage to the rabbit and hare to be colored
like earth; black or white rabbits are more easy to see, and
consequently more likely to be killed. This, however, does not apply
to those which are kept in captivity, and we know that tame rabbits
are often black and white. Again, in the far north, where for months
together the ground is covered with snow, the white color, which would
be a danger here, becomes an advantage; and many Arctic animals, like
the polar bear and polar hare, are white, while others, such as the
mountain hare and ptarmigan, change their color, being brown in summer
and white in winter. So are the Arctic fox and the ermine, to whom it
is then an advantage to be white, not to avoid danger, but in order
that they may be the more easily able to steal unperceived upon their
prey.
Many of the cases in which certain insects escape danger by their
similarity to plants are well known; the leaf insect and the
walking-stick insect are familiar and most remarkable cases. The larvae
of insects afford, also, many interesting examples, and in other
respects teach us, indeed, many instructive lessons. It would be a
great mistake to regard them as merely preparatory stages in the
development of the perfect insect. They are much more than this, for
external circumstances act on the larvae, as well as on the perfect
insect: both, therefore, are liable to adaptation. In fact, the
modifications which insect larvae undergo may be divided into two
kinds--developmental, or those which tend to approximation to the
mature form; and adaptational or adaptive, those which tend to suit
them to their own mode of life.
It is a remarkable fact, that the forms of larvae do not depend on
those of the mature insect. In many cases, for instance, very similar
larvae produce extremely dissimilar insects. In other cases, similar,
or comparatively similar, perfect insects have very dissimilar larvae.
Indeed, a classification of insects founded on larva would be quite
different from that founded on the perfect insects. The group to which
the bees, wasps, and ants belong, for instance, and which, so far as
the perfect insects are concerned, form a very natural division, would
be divided into two; or rather one portion of them--namely, the
saw-flies--would be united to the butterflies and moths. Now, why do
the larvae of saw-flies differ from those of their allies, and resemble
those of butterflies and moths? It is because their habits differ from
those of ants and bees, and they feed on leaves like ordinary
caterpillars.
In some cases the form changes considerably during the larval state.
From this point of view, the transformations of a small beetle, called
_Sitaris_, which have been carefully observed by M. Fabre, are
peculiarly interesting.
The genus Sitaris, which is allied to the blister-fly and to the
oil-beetle, is parasitic on a kind of solitary bee which excavates
subterranean galleries, each leading to a cell. The eggs of the
beetle, which are deposited at the entrance of the galleries made by
the bees, are hatched at the end of September or beginning of
October, and we might not unnaturally expect that the young larvae,
which are active little creatures with six serviceable legs, would at
once eat their way into the cells of the bee. No such thing: till the
month of April following they remain without leaving their birthplace,
and consequently without food; nor do they in this long time change
either in form or size. M. Fabre ascertained this, not only by
examining the burrow of the bees, but also by direct observations of
some young larvae kept in captivity. In April, however, his captives at
last awoke from their long lethargy, and hurried anxiously about their
prisons. Naturally inferring that they were in search of food, M.
Fabre supposed that this would consist either of the larvae or pupae of
the bee, or of the honey with which it stores its cell. All three were
tried without success. The first two were neglected; and the larvae,
when placed on the latter, either hurried away or perished in the
attempt, being evidently unable to deal with the sticky substance. M.
Fabre was in despair. The first ray of light came to him from our
countryman Newport, who ascertained that a small parasite found on one
of the wild bees was, in fact, the larva of the oil-beetle. The larvae
of Sitaris much resembled this larva. Acting on this hint, M. Fabre
examined many specimens of the bee, and found on them at last the
larvae of his Sitaris. The males of the bee emerge from the pupae sooner
than the females, and M. Fabre ascertained that, as they come out of
their galleries, the little Sitaris larvae fasten upon them. Not,
however, for long: instinct teaches them that they are not yet in the
straight path of development; and, watching their opportunity, they
pass from the male to the female bee. Guided by these indications, M.
Fabre examined several cells of the bee; in some, the egg of the bee
floated by itself on the surface of the honey; in others, on the egg,
as on a raft, sat the still more minute larva of the Sitaris. The
mystery was solved. At the moment when the egg is laid, the Sitaris
larva springs upon it. Even while the poor mother is carefully
fastening up her cell, her mortal enemy is beginning to devour her
offspring; for the egg of the bee serves not only as a raft, but as a
repast. The honey, which is enough for either, would be too little for
both; and the Sitaris, therefore, at its first meal, relieves itself
from its only rival. After eight days the egg is consumed, and on the
empty shell the Sitaris undergoes its first transformation, and makes
its appearance in a very different form.
The honey, which was fatal before, is now necessary--the activity,
which before was necessary, is now useless; consequently, with the
change of skin, the active, slim larva changes into a white fleshy
grub, so organized as to float on the surface of the honey, with the
mouth beneath and the breathing-holes above the surface; for insects
breathe, not as we do through the mouth, but through a row of holes
arranged along the side. In this state it remains until the honey is
consumed; then the animal contracts, and detaches itself from its
skin, within which the further transformations take place. In the next
stage the larva has a solid corneous envelope and an oval shape, and,
in its color, consistency, and immobility, resembles the chrysalis of
a fly. The time passed in this condition varies much. When it has
elapsed, the animal moults again, again changes its form; after this,
it becomes a pupa, without any remarkable peculiarities. Finally,
after these wonderful changes and adventures, in the month of August
the perfect beetle makes its appearance.
[Illustration: FIG. 1. THE CATERPILLAR OF THE MARBLED WHITE BUTTERFLY
(_Arge galathea_).]
In fact, whenever in any group we find differences in form or color,
we shall always find them associated with differences in habit. Let us
take the case of Caterpillars. The prevailing color of caterpillars is
green, like that of leaves. The value of this to the young insect, the
protection it affords, are obvious. We must all have observed how
difficult it is to distinguish small green caterpillars from the
leaves on which they feed. When, however, they become somewhat larger,
their form betrays them, and it is important that there should be
certain marks to divert the eye from the outlines of the body. This is
effected, and much protection is given, by longitudinal lines (Fig. 1),
which accordingly are found on a great many caterpillars. These
lines, both in color and thickness, much resemble some of the lines on
leaves (those, for instance, of grasses), and also the streaks of
shadow which occur among foliage. If this be the explanation of them,
then they ought to be wanting, as a general rule, in very small
caterpillars, and should prevail most among those which feed on or
among grasses.
[Illustration: FIG. 2.--THE CATERPILLAR OF THE EYED HAWK-MOTH
(_Smerinthus ocellatus_).]
Now, similar lines occur on a great number of caterpillars belonging
to most different groups of butterflies and moths, as you may see by
turning over the illustrations of any monograph of the group. They
exist among the Hawk-moths--as, for instance, in the Humming-bird
Hawk-moth; they occur in many butterflies, especially in those which
feed on grass; and in many moths. But you will find that the smallest
caterpillars rarely possess these white streaks. As regards the second
point, also, the streaks are generally wanting in caterpillars which
feed on large-leaved plants. The _Satyridae_, on the contrary, all
possess them, and all live on grass. In fact we may say, as a general
rule, that these longitudinal streaks only occur on caterpillars which
live on or among narrow-leaved plants. As the insect grows, these
lines often disappear on certain segments, and are replaced by
diagonal lines. These diagonal lines (Fig. 2) occur in a great many
caterpillars, belonging to the most distinct families of butterflies
and moths. They come off just at the same angle as the ribs of leaves,
and resemble them very much in general effect. They occur also
especially on species which feed on large-leaved plants; and I believe
I may say that though a great many species of caterpillars present
these lines, they rarely, if ever, occur in species which live on
grass; while, on the contrary, they are very frequent in those
species which live on large-leaved plants.
It might at first be objected to this view that there are many cases,
as in the Elephant-Hawk-moth, in which caterpillars have both. A
little consideration, however, will explain this. In small
caterpillars these oblique lines would be useless, because they must
have some relation, not only in color, but in their distance apart, to
the ribs of the leaves. Hence, while there are a great many species
which have, longitudinal lines when young, and diagonal ones when they
are older and larger, there is not, I believe, a single one which
begins with diagonal lines, and then replaces them with longitudinal
ones. The disappearance of the longitudinal lines on those segments
which have diagonal ones, is striking, where the lines are marked. It
is an advantage, because white lines crossing one another at such an
angle have no relation to anything which occurs in plants, and would
make the creature more conspicuous. When, therefore, the diagonal
lines are developed, the longitudinal ones often disappear. There is
one other point in connection with these diagonal lines to which I
must call your attention.
In many species they are white, but in some cases--as, for instance,
in the beautiful green caterpillar of the Privet-Hawk-moth--the white
streak is accompanied by a colored one, in that case lilac. At first
we might think that this would be a disadvantage, as tending to make
the caterpillar more conspicuous; and in fact, if we put one in full
view--for instance, out on a table--and focus the eye on it, the
colored lines are very striking. But we must remember that the habit
of the insect is to sit on the lower side of the leaf, generally near
the middle rib, and in the subdued light of such a situation,
especially if the eye be not looking exactly at them, the colored
lines beautifully simulate a line of soft shadow, such as must always
accompany a strong rib; and I need not tell any artist that the
shadows of yellowish-green must be purplish. Moreover, any one who has
ever found one of these large caterpillars will, I am sure, agree with
me that it is surprising, when we consider their size and conspicuous
coloring, how difficult it is to see them.
But though the prevailing color of caterpillars is green, there are
numerous exceptions. In one great family of moths the prevailing color
is brown. These caterpillars, however, escape observation by their
great similarity to brown twigs--a resemblance which is heightened by
their peculiar attitudes, and in many cases by the existence of warts
or protuberances, which look like buds. Some, however, even of these
caterpillars, when very young, are green. Again, some caterpillars are
white. These feed on and burrow in wood. The Ringlet Butterfly also
has whitish caterpillars, and this may at first sight appear to
contradict the rule, since it feeds on grass. Its habit is, however,
to keep at the roots by day, and feed only at night.
In various genera we find Black caterpillars, which are of course very
conspicuous, and, so far as I know, not distasteful to birds. In such
cases, however, it will be found that they are covered with hairs or
spines, which protect them from most birds. In these species the bold
dark color may be an advantage, by rendering the hair more
conspicuous. Many caterpillars are black and hairy, but I do not know
any large caterpillar which is black and smooth.
Brown caterpillars, also, are frequently protected by hairs or spines
in the same way; but, unlike black ones, they are frequently naked.
These fall into two principal categories: firstly, those which, like
the Geometridae, put themselves into peculiar and stiff attitudes, so
that in form, color, and position they closely resemble bits of dry
stick; and, secondly, those which feed on low plants, concealing
themselves on the ground by day, and only coming out in the dark.
Yellow and yellowish-green caterpillars are abundant, and their color
is a protection. Red and blue, on the contrary, are much less common
colors, and are generally present as spots.
Moreover, caterpillars with red lines or spots are generally hairy,
and this for the reason given above. Such species, therefore, would be
avoided by birds. There are, no doubt, some apparent exceptions. The
Swallow-tail Butterfly, for instance, has red spots and still is
smooth; but as it emits a strongly-scented liquid when alarmed, it is
probably distasteful to birds. I cannot recall any other case of a
British caterpillar which has conspicuous red spots or lines, and yet
is smooth.
Blue is, among caterpillars, even a rarer color than red. Indeed,
among our larger larvae, the only cases I can recall are the Lappets,
which have two conspicuous blue bands, the Death's-head Moth, which
has broad diagonal bands, and two of the Hawk-moths, which have two
bright blue oval patches on the third segment. The Lappets are
protected by being hairy, but why they have the blue bands I have no
idea. It is interesting, that both the other species frequent plants
which have blue flowers. The peculiar hues of the Death's-head
caterpillar, which feeds on the potato, unite so beautifully the brown
of the earth, the yellow and green of the leaves, and the blue of the
flowers, that, in spite of its size, it can scarcely be perceived
unless the eye be focussed exactly upon it.
The Oleander Hawk-moth is also an interesting case. Many of the
Hawk-moth caterpillars have eye-like spots, to which I shall have to
allude again presently. These are generally reddish or yellowish, but
in this species, which feeds on the periwinkle, they are bright blue,
and in form as well as color closely resemble the blue petals of that
flower. One other species, the Sharp-winged Hawk-moth, also has two
smaller blue spots, with reference to which I can make no suggestion.
It is a very rare species, and I have never seen it. Possibly, in this
case, the blue spots may be an inherited character, and have no
reference to the present habits. They are, at any rate, quite small.
No one who looks at any representations of Hawk-moth caterpillars can
fail to be struck by the peculiar coloring of those belonging to the
Pine Moth, which differ in style of coloring from all other sphinx
larvae, having longitudinal bands of brown and green. Why is this?
Their _habitat_ is different. They feed on the leaves of the pinaster,
and their peculiar coloring offers a general similarity to the brown
twigs and narrow green leaves of a conifer. There are not many species
of butterflies or moths which feed on the pine, but there are a few:
and most, if not all of them, have a very analogous style of coloring
to that of the Pine Moth, while the latter has also tufts of
bluish-green hair which singularly mimic the leaves of the pine. It is
still more remarkable that in a different order of insects we again
find species--for instance one of the saw-flies--which live on the
pine, and in which the same style of coloring is repeated.