Butterflies Worth Knowing Part 3

THE MONARCH b.u.t.tERFLY: CHANGE FROM CATERPILLAR TO CHRYSALIS.

Photographs from life. (_See pages 8-10, 233_)]

[Ill.u.s.tration: Chrysalis showing b.u.t.terfly ready to emerge The empty chrysalis b.u.t.terfly just out of chrysalis Side view a little later

THE MONARCH b.u.t.tERFLY: THE CHANGE FROM CHRYSALIS TO ADULT.

Photographs from life (_See pages 10-13, 235_)]

[Ill.u.s.tration: _See page 30_

THE CAROLINA LOCUST Above, with wings expanded as in flight]

SELECTIVE COLOR SENSE

One who collects the Underwing moths soon discovers that the light colored species which resemble the bark of birch trees are likely to be found upon the trunks of those trees, and that the dark colored kinds which resemble the bark of maple trees are likely to be found upon the trunks of these. Obviously, were this not true the protective coloring would avail but little and it is evident that these moths are able to select a background which is of advantage in helping to conceal them.

There is much evidence to show that in a similar way the b.u.t.terflies are able by means of a well-developed color sense to select the places where they alight. One of the most notable examples is that of a South American species, _Peridromia feronia_. This is a silvery gray b.u.t.terfly which alights head downward upon the bark of certain palm trees that have silvery gray stems and remains there with its wings fully expanded so that it utilizes the background in much the same way that the Underwing moths do. "When disturbed they will return to the same tree again and again."

One who will observe the habits of our Angle-wings and other b.u.t.terflies which have obliterative coloring of the under wing surface can easily learn that these insects select rather carefully the places where they alight. It will be found that as a rule each species utilizes a background that blends with its own coloring. It is probable that this habit is much more common in other groups of b.u.t.terflies than has been realized. Much evidence of this sort has been collected regarding the b.u.t.terflies of Europe and other countries, as well as near our own borders in America.

WARNING COLORATION AND MIMICRY

The colors of a great many animals, including a considerable percentage of American b.u.t.terflies and their larvae, have been commonly explained by the theory of _warning colors_. According to this theory animals which were for any reason not edible by birds and mammals have developed various striking combinations of color such as black and yellow, red and black, or black and white, in order to advertise to their foes their inedible qualities. This theory has been very generally accepted by naturalists and will be found expounded at length in many books published during the last quarter century.

The whole subject of the validity of warning coloration has recently been brought up for reconsideration by the illuminating investigations of Mr. Abbott H. Thayer and discussed at length in the book upon "Concealing Coloration" already mentioned. In an appendix to this book dated 1908 Mr. Thayer states that he no longer holds the belief that "there must somewhere be warning colors." He has convincingly shown that a large proportion of the animals which were supposed to be examples of this theory are really ill.u.s.trations of concealing coloration. But there yet remain various facts which have been conclusively proven that apparently require the theory of warning colors to explain them. Here is another field in which there is a real need for much careful investigation under conditions that are rigidly scientific.

Along with the theory of warning coloration the theory of _mimicry_ has been propounded. According to this if a b.u.t.terfly in a given region shows warning coloration, having developed such coloration because it is distasteful to birds and mammals, it may be mimicked by another b.u.t.terfly in the same region belonging to another group, the latter b.u.t.terfly being edible, but benefiting by its resemblance to the distasteful species, because birds or mammals mistake it for the latter and do not attempt to catch it. The most notable example of such mimicry in North America is that of the Monarch b.u.t.terfly, which is supposed to be the distasteful species, and the Viceroy b.u.t.terfly, which is supposed to mimic it. Several other instances of mimicry are found among our own b.u.t.terflies, while in South America, Africa, and Asia there are numberless examples.

HELIOTROPISM

It has long been known that the green surfaces of plants respond to the stimulus of the sun's rays in a most remarkable manner. This response has commonly been called _heliotropism_ and it has been carefully studied by botanists all over the habitable world. More recently, the fact has been observed that many animals respond in certain definite ways to the stimulus of direct suns.h.i.+ne and the same term has been applied in this case. Very little attention has been given to the subject of heliotropism until within a few recent years.

But the observations which have been made by Parker, Longstaff, Dixey, and others open up a most interesting field for further observation.

An admirable summary of our present knowledge of the subject has been published by Dr. Longstaff in his book "b.u.t.terfly Hunting in Many Lands."

One of the earliest observations upon this subject was that published in my book "Nature Biographies" which appeared in June, 1901, concerning the habit in the Mourning Cloak: "On a spring-like day early in November (the 8th) I came across one of these b.u.t.terflies basking in the suns.h.i.+ne upon the ties of a railway track. It rested with its wings wide open. On being disturbed, it would fly a short distance and then alight, and I was interested to notice that after alighting it would always turn about until the hind end of its body pointed in the direction of the sun, so that the sun's rays struck its wings and body nearly at right angles. I repeatedly observed this habit of getting into the position in which the most benefit from the suns.h.i.+ne was received, and it is of interest as showing the extreme delicacy of perception toward the warmth of suns.h.i.+ne which these creatures possess."

A little later, some very elaborate observations were made upon this habit of the Mourning Cloak by Prof. G. H. Parker of Harvard University. Professor Parker noticed that during the warm spells in winter the b.u.t.terflies came out of their hiding places and after alighting, always placed themselves with their heads away from the direction of the sun and their bodies lying nearly at right angles to the sun's rays. By experiment, he found that they adjusted themselves to this position as soon as they were fully exposed to direct suns.h.i.+ne, even if at the time of alighting they were in a shadow. He found that this movement was a reflex action through the eyes, for when the eyes were blinded no such adjustment took place. He called it _negative heliotropism_.

Dr. Longstaff uses the term _orientation_ for this adjustment of the b.u.t.terfly to the sun's rays and he finds it is a very general habit, especially with the Angle-wings, for the b.u.t.terfly thus to orient itself after alighting, in such a way that the hind end of the body points toward the sun. This occurs not only with those species which keep their wings spread open when they alight but also with those in which the wings are closed together and held in a vertical position on alighting.

Various explanations of this phenomenon have been offered but apparently none of them are yet generally accepted. Were the habit confined to b.u.t.terflies like the Mourning Cloak, it would seem easy to prove that a main advantage was found in the benefit derived from the heat rays of the sun. Were it confined to those species which always fold their wings on alighting, it would seem easy to believe that it was a device for reducing the shadow cast by the insect to its lowest terms. It has also been suggested that the habit is for the purpose of revealing to the fullest extent the markings of the b.u.t.terfly.

Evidently there is here an ample field for further investigation before definite conclusions are reached.

LIST AND SHADOW OBSERVATIONS

Another field for most interesting studies upon the habits of living b.u.t.terflies has been opened up by the very interesting discussion of _list and shadow_ in Colonel G. B. Longstaff's fascinating book, "b.u.t.terfly Hunting in Many Lands." He there summarizes his numerous observations upon b.u.t.terflies in various localities which he has seen to lean over at a decided angle when they alight. He defines "_List_"

as "an att.i.tude resulting from the rotation of the insect about its longitudinal axis, as heliotropism results from a rotation about an imaginary vertical axis at right angles to this." The name is adapted from the sailors' term applied to a vessel leaning to one side or another in a storm.

Apparently this interesting habit was first called to the attention of European entomologists by an observation of Colonel C. T. Bingham made in 1878, but not published until long afterward. The observation was this:

"The _Melanitis_ was there among dead leaves, its wings folded and looking for all the world a dead, dry leaf itself. With regard to Melanitis, I have not seen it recorded anywhere that the species of this genus when disturbed fly a little way, drop suddenly into the undergrowth with closed wings, and invariably lie a little askew and slanting, which still more increases their likeness to a dead leaf casually fallen to the ground."

Long before this was printed, however, a similar habit had been observed by Scudder in the case of our White Mountain b.u.t.terfly (_Oenis semidea_). But this species is so exceptional in its habitat that the habit seems to have been considered a special adaptation to the wind-swept mountain top. The possibility of its being at all general among the b.u.t.terflies in lowlands seems to have been overlooked.

The observations recorded by Longstaff relate chiefly to various members of the Satyrid group. For example, a common Grayling, _Satyrus semele_, was watched many times as it settled on the ground. As a rule three motions are gone through in regular sequence: the wings are brought together over the back; the forewings are drawn between the hind wings; the whole is thrown over to right or left to the extent of thirty, forty, or even fifty degrees.

This habit, of course, is of advantage to the insect. It seems possible that the advantage might be explained in either of two ways: first, the leaning over on the ground among gra.s.ses and fallen leaves might help to render the disguising coloration of the insect more effective, the large ocelli serving to draw the eye away from the outline of body and wing; second, the listing of the b.u.t.terfly toward the sun tends to reduce the shadow and to hide it beneath the wings.

There is no doubt that when a Grayling b.u.t.terfly lights upon the ground in strong suns.h.i.+ne the shadow it casts is more conspicuous than the insect itself and the hiding of this might be of distinct advantage in helping it to escape observation. It is significant that in England the b.u.t.terflies observed appear to lean over more frequently in suns.h.i.+ne than in shade. An observation of Mr. E. G.

Waddilove, reported by Colonel Longstaff, is interesting in this connection:

"A Grayling settled on a patch of bare black peat earth, shut up its wings vertically, and crawled at once some two yards to the edge of the patch to where some fir-needles, a cone or two, and a few brittle twigs were lying, and then becoming stationary threw itself over at an angle of some forty-five degrees square to the sun. It thus became quite indistinguishable from its surroundings."

Apparently, some of the Angle-wings may have the same habit, for in Barrett's "Lepidoptera of the British Islands," there is a note in regard to _Grapta C-alb.u.m_ to the effect that it is fond of sunning itself in roads, on warm walls, or on the ground upon dead leaves in sheltered valleys. "Here, if the sun becomes overclouded, it will sometimes close its wings and almost lie down, in such a manner that to distinguish its brown and green marbled under side from the dead leaves is almost impossible."

Here is a most fascinating opportunity for American observers to determine definitely the facts in regard to our numerous species of b.u.t.terflies that may show this habit. An observer with a reflex type of camera might easily be able to get pictures that would be of great value in helping to determine the princ.i.p.al facts in regard to the subject. Our common Graylings and numerous species of Angle-wings are so abundant and easily observed that they offer splendid opportunities to any one who will undertake a serious study of the subject.

PARASITIC ENEMIES

All three of the earlier stages of b.u.t.terflies--egg, larva, and chrysalis--are subject to attack by various parasitic insects which develop at the expense of the host. Such parasites are probably the most important check upon the increase of b.u.t.terflies, and along with birds, mammals, and bacterial diseases, they help to keep up that balance of nature which in the long run maintains a surprising uniformity in the numbers of each kind of b.u.t.terfly.

For the most part these insect parasites are small four-winged flies, although many of them are two-winged flies. In either case the life stages show a series of changes much like those of the b.u.t.terflies themselves. Each parasite exists first as an egg, second as a larva, third as a pupa, and fourth as an adult fly. The larval stage, however, is simply that of a footless grub which lives within the body of its victim absorbing its life blood and gradually killing it.

The parasites of b.u.t.terfly eggs are legion. They are tiny flies whose life-story in briefest summary is this: The b.u.t.terfly lays an egg. The parasite fly finds this egg soon after it is laid, and pierces the sh.e.l.l with her tiny, sharply pointed ovipositor and deposits inside of the sh.e.l.l her own microscopic egg. This egg within the egg soon hatches into a curious little larva that develops at the expense of the contents of the b.u.t.terfly egg sh.e.l.l, and soon absorbs the whole of them. The parasite larva now changes to a pupa which a little later changes again to an adult fly like the one that laid the parasite egg in the beginning. Of course the b.u.t.terfly egg never hatches into a caterpillar.

One of the most interesting questions in regard to these egg parasites is this: How does the tiny parasitic fly find the newly laid egg? One would think that the proverbial search for a needle in a haymow would be an easy task compared with that of a fly about as large as the head of a pin finding a b.u.t.terfly egg of similar size upon some part of one of the millions of leaves upon the trees and shrubs in field and forest. Yet the search is successful, as every one who has tried to get caterpillars from eggs found out of doors will testify. On a later page in this book, in connection with the story of the life of the Mourning Cloak b.u.t.terfly, I have recorded some observations upon the little parasite which seemed to have been riding around upon the body of the b.u.t.terfly waiting for her to lay her eggs.

For one parasite upon the eggs of b.u.t.terflies, there probably are dozens that attack the caterpillars. A large proportion of the b.u.t.terfly larvae brought in from outdoors, especially those which are half-grown or more, will yield not b.u.t.terflies but parasites. This is the experience of practically every one who attempts to rear these insects, and it emphasizes the value of the advice that in order to get fine specimens, it is desirable to rear them from eggs laid by b.u.t.terflies beneath netting or in cages.