The life-histories of the parasites that attack caterpillars vary greatly. The simplest are those of the large Ichneumon flies: The mother fly lays an egg beneath the skin of the caterpillar. The egg hatches into a larva that absorbs the fatty parts of the body of the caterpillar, gradually growing larger and larger until at last it reaches a length of possibly an inch. By this time it is likely to have absorbed so large a part of the inside of the caterpillar that the latter dies. The parasite larva now changes to a pupa, either inside or outside the skin of the caterpillar, and a little later changes again to an adult Ichneumon fly.

[Ill.u.s.tration: Tachinid Parasite: _a_, fly; _b_, puparium, magnified.]

In the case just given, one egg only was deposited within the skin of the caterpillar. In many others, however, a large number of eggs may be so deposited by a single fly. A special group of Ichneumon flies, called the Microgasters, contains many parasites that have this peculiarity. The Microgaster larvae on coming forth from the caterpillar have the habit of spinning tiny coc.o.o.ns within which they change to pupae. By collecting some cabbage worms which are nearly full grown, and keeping them in a gla.s.s jar one can generally get a considerable number of these Microgaster coc.o.o.ns and rear the flies from them.

Another group of caterpillar parasites is still more minute. They are called the Chalcid flies. Their life-histories are full of interest, and might easily furnish opportunity for a long lifetime of study and experiment. One is likely to get hundreds of these Chalcid flies from a single caterpillar.

Another interesting group of parasites is that of the two-winged Tachina flies (_see cut on this page_). The life-story of some of these is comparatively simple: a buzzing fly, looking much like a large housefly, lays a small whitish egg upon the skin of a caterpillar. This egg is glued tightly and is large enough to be readily seen by the unaided eye. It hatches into a tiny larva that eats its way through the part of the sh.e.l.l glued to the caterpillar's skin, and through the latter at the same time. So the newly hatched Tachina larva finds itself in the body of its caterpillar host. It lives there, absorbing the fatty juices around it until at last it either kills or stupefies its unfortunate victim. It has then become full grown as a larva, and its last larval skin hardens into a brown pupa-case within which the little creature changes into a pupa. It may or may not have burrowed through the skin of the caterpillar before this happened. A little later the pupa changes to a Tachina fly which breaks apart the pupa-case and flies out into the world.

It has lately been found, however, that many Tachinids have much more complicated life-histories than this. I have already discussed some of the more important of these in my book ent.i.tled, "Seeing Nature First"

(_pages 150-158_).

One can frequently rear parasites from the chrysalids of b.u.t.terflies, but in many cases it is probable that these began their parasitic development in the caterpillars, which were able to change to chrysalids before being killed. In some cases, however, the chrysalids seem to be attacked, especially by certain Ichneumon flies.

REARING b.u.t.tERFLIES FROM CATERPILLARS

There are few things in the world more interesting to watch than the wonderful changes which a moth or b.u.t.terfly goes through in the course of its life. You find on a tree or shrub a worm-like caterpillar. You take it in charge, placing it in a box or jar where you can provide leaves for its food and soon it either spins around itself a silken shroud, thus hiding from your sight, or else it simply seems to change to a lifeless object without eyes or wings or legs, unable to move about and motionless, save for a slight wriggle when you touch it. Yet if you keep the shroud or the mummy-like object for two or three weeks you are likely to see a beautiful moth come from the shroud or a glorious b.u.t.terfly break out of the mummy case. (_See plate, page 49._) So you can get the realest kind of moving pictures by simply bringing in the caterpillars that are easily found in garden, field, and wood.

To collect these caterpillars it is only necessary to be provided with a pair of sharp eyes and an empty coffee can or some other form of tin box. Go out into the garden or along the borders of the woods. Look carefully. If you see places where leaves have been eaten, search the leaves near by and you are likely to find one or more of the caterpillars that caused the injury. Transfer them to the box and take them home with a few leaves of the food plant. There place them in some form of vivarium, which simply means a box or cage in which you can keep living creatures.

The most satisfactory cages for rearing caterpillars are those which are open above so that there is not even a gla.s.s plate between the observer and the insect. This kind of vivarium is easily made by using a band of some sticky substance like the tree tanglefoot with which trees are commonly banded, or a strip of sticky fly paper. Any wide shallow box may be used by simply placing an inch-wide band of the sticky material around the vertical sides near the top. The caterpillars will be free to move all over the open box but they cannot cross the band to escape. Fresh leaves are easily placed in the open box and the withered ones removed.

The same plan may be adopted with wide gla.s.s jars, like the ordinary battery jar. Choose a rather large one and smear the inner side near the top with a band of sticky material. The caterpillars are thus prevented from crawling out, but they are open to observation at all times. (_See plate, pages 48-49._)

In the case of the caterpillars that change to b.u.t.terflies no soil need be placed in the bottom of the jar as these will attach their chrysalids to the sides or to a stick or board which may easily be put in. In the case of many caterpillars that change to moths, however, it is desirable to place about two inches of soil in the bottom of the jar. Then if the caterpillars are not coc.o.o.n spinners they can burrow into the soil when they are ready to change to pupae.

Instead of applying the sticky material directly to the gla.s.s a strip of sticky fly paper may be glued to it.

As a rule the b.u.t.terfly caterpillar easiest to find lives upon cabbages. Go into the garden and you are likely to see a dozen green caterpillars upon as many cabbage plants. Bring in several of the larger ones and place them in a vivarium with some fresh cabbage leaves. In a few days some of them will be likely to fasten themselves to the vertical sides of the vivarium and shed the caterpillar skin.

Each thus becomes a chrysalis. About ten days later this chrysalis skin will break open and a white Cabbage b.u.t.terfly will come out.

So your caterpillar goes through the four different stages of insect life. It was first an egg laid upon the leaf by a b.u.t.terfly; the egg hatched into the caterpillar or larva; the larva changed to the chrysalis; the chrysalis changed to the b.u.t.terfly or adult insect.

One of the most satisfactory ways to rear the caterpillars of b.u.t.terflies is to get the females to lay their eggs upon the food plant. In the case of many species this is not difficult. The simplest way is to enclose the mother b.u.t.terfly in a small gauze bag tied over the branch of the food plant. If she has eggs ready to deposit she is very likely to lay them under these conditions. After they are laid the mother b.u.t.terfly may be allowed to escape, but it is well to replace the gauze protection as a safeguard against many sorts of enemies which may destroy the eggs or the young caterpillars that hatch from them. Another way is to enclose the b.u.t.terflies with a twig of the food plant in a gla.s.s jar, sealing it tight to prevent the leaves from wilting. The b.u.t.terfly is likely after she has quieted down to lay her eggs upon the leaves. According to William G. Wright, who speaks from his long experience with the b.u.t.terflies of the West Coast, these genera will lay their eggs on anything: Parna.s.sius, Argynnis, Euptoieta, Neonympha, and all members of the family Satyridae. In these cases one can get the eggs by simply enclosing the b.u.t.terflies in gla.s.s jars or gauze nets without even the leaves of the food plant. William H. Edwards found in his long experience that one can get the eggs of practically all b.u.t.terflies in confinement, provided only the insects are sufficiently mature so that the eggs are ready to be laid. He found that the cause of failure to get eggs from many of the Fritillaries early in the season was that the eggs were not mature and that from the same kinds of b.u.t.terflies with which he failed early in the summer he got plenty of eggs in September.

There is here a rich field for observation and experiment for every naturalist who wishes to take up the study of b.u.t.terflies. He can be sure of the parentage of the caterpillars and can trace them from the very moment of egg-laying through all their wonderful changes until they become b.u.t.terflies again.

PHOTOGRAPHING b.u.t.tERFLIES

There is a famous old saying that to make hare stew it is first necessary to catch your hare. So if one wishes to make perfect pictures of b.u.t.terflies it is first necessary to get the caterpillars.

For though caterpillars are not b.u.t.terflies they are b.u.t.terflies in the making and they will show you most interesting stages in nature's manufacture of these dainty and exquisite creatures. This is not, however, the chief reason why the photographer should get them. He will wish to make perfect pictures and in order to do this he must have not only perfect specimens but living b.u.t.terflies which are willing to look pleasant while he makes comparatively long exposures under conditions of light that he can control. If you catch a b.u.t.terfly outdoors and bring it in you will be likely to find that it is by no means a docile subject. The sunlight shining through the nearest window will be a call which you cannot counteract and your b.u.t.terfly will constantly respond to it in a most vexing manner. So you must catch the b.u.t.terfly young and take advantage of a brief but docile period in their lives when they are willing to pose before your camera in quite a remarkable manner. This is the period just after the b.u.t.terfly emerges from the chrysalis when its wings are fully developed but before the tissues have hardened and the muscles in the thorax are strong enough for flight. At this time the b.u.t.terfly is perfect, every scale is in its place and every spot of color is at its best, and it will rest quietly upon a flower, leaf, or twig while you adjust the camera and expose the plate. From one such specimen one can get many pictures upon different flowers and with different angles of view. (_See plates, pages 160, 225._)

In order to make admirable photographs of living b.u.t.terflies it is by no means necessary to have a regular photographic studio. If one has a room lighted from the north or east one can arrange for exposure near the window, using cardboard reflectors to make the light more even from both sides. In such a situation one soon learns the exposure periods required and can easily get many beautiful photographs.

A collection of prints of the b.u.t.terflies of one's locality would be one of the most interesting photographic exhibits that an amateur could select. It is comparatively easy to get rather full sets showing the life-histories of several of our larger species and such sets are of course of especial interest. In the case of those caterpillars which make nests upon the food plant, like the Painted Beauty larva which remains for weeks feeding upon the leaves of the common wild everlasting, the taking of the pictures of the different stages is comparatively easy. One can keep the plant with the stem in water, and get the caterpillar to change to the chrysalis, and emerge as the b.u.t.terfly, in the nest made from the flower heads and the upper leaves.

[Ill.u.s.tration: _From a drawing by W. I. Beecroft_ _See page 59_

THE BLACK SWALLOWTAIL Caterpillar, chrysalis and b.u.t.terfly]

[Ill.u.s.tration: Two hundred Monarchs resting on one dead limb]

[Ill.u.s.tration: _Photographed by Craig S. Thomas_ _See pp. 16, 235_ "When a stick was thrown into the tree the air was full of Monarchs"

A MIGRATION OF MONARCH b.u.t.tERFLIES]

[Ill.u.s.tration: _See page 45_

THE IMPROVED OPEN VIVARIUM]

[Ill.u.s.tration: _From a photograph from life by A. H. Verrill._ _See page 14_

THE CYNTHIA MOTH AND THE COc.o.o.n FROM WHICH IT CAME]

b.u.t.tERFLY COLLECTIONS

There are few groups in Nature which offer such advantages to the collector as that of the b.u.t.terflies. They are easily obtained, easily preserved, and retain their beauty for a long period even under exposure to strong light. They offer opportunities for serious study in which one cannot only review the facts which others have already discovered, but also hope to contribute something of value to the sum of human knowledge.

The mistake most commonly made by beginners with b.u.t.terflies, as with other collections, is to undertake too much. Instead of starting on the hopeless task of making a collection of the b.u.t.terflies of the world, it is much better to start with the intention of making a collection of those of one's own town. In the latter case one can hope soon to attain the desired end and then, if one wishes, it is a simple matter to reach out and make a collection of the b.u.t.terflies of the state or even of the particular region in which the state is located.

The natural limitations for a collection in New England is to make a collection of New England b.u.t.terflies. There is a splendid example of such a collection on exhibition in the museum of the Boston Society of Natural History. This contains representatives of practically every kind that has been collected in New England, and yet there are less than a hundred species in all. So it is apparent that a local collection should be attainable by any enthusiastic student and the very fact that the number of species is limited adds interest and satisfaction to the pursuit.

The main value of any collection of objects lies in the point of view of the collector. The most natural point of view for a beginner is that of the local fauna, as indicated in the previous paragraph. Such a collection best serves as a basis for a study of the subject but it may well lead to a broader field through some special phase of scientific interest. Thus while it would be hopeless for most persons to attempt a collection of the b.u.t.terflies of the world it would be entirely reasonable for one to start a collection of all the species in the world of any given genus or tribe, and such a set of specimens would soon come to possess decided scientific value. Or, instead of the point of view of generic or family relationship, one could take the point of view of special geographical distribution. Thus a collection of all the b.u.t.terflies found within a certain number of degrees of the North Pole showing the circ.u.mpolar b.u.t.terfly fauna would have great scientific interest.

There are also various other points of view which could be followed in making a collection. There are already in many of the museums of the world collections of b.u.t.terflies which ill.u.s.trate the various phases of true mimicry--the resemblance of one species to another in the same region. This is a field in which one could spend a lifetime of endeavor, and secure results of great value to the world of science.

An easier problem for most collectors in the United States would be a collection made from the point of view of resemblance to environment, including such examples as the Angle-wings that show a bark-like set of marks on the under surface. Yet another point of view would be that of hibernation, the making of a collection of all b.u.t.terflies that hibernate as adults.

These are only a few suggestions. There are many other phases of b.u.t.terfly life which could be utilized as the basis for interesting collections. The important thing is to have a definite object in view and to make the collection a basis for a real study of the subject, so that the collector will not only be growing intellectually but will also be making a real contribution to our scientific knowledge.

_Collecting Apparatus_

To collect and preserve b.u.t.terflies in proper condition for study, certain apparatus is necessary. Perhaps the first essential is the collecting net for catching b.u.t.terflies in the field. The simplest way to obtain this is to buy it of the dealers in entomological supplies.