Butterflies Worth Knowing Part 8

The most familiar and abundant American b.u.t.terflies are cla.s.sified together under the family name _Pieridae_, or the Pierids. Three groups or tribes of them are popularly known as the Whites, the Orange-tips, and the Yellows. Our two commonest b.u.t.terflies, the White or Imported Cabbage b.u.t.terfly and the Sulphur Yellow b.u.t.terfly, are typical representatives of this family. Most of the rest, like these, are of moderate size with rounded wings which are more or less marked with black. There are six well-developed legs and the caterpillars of practically all the species are cylindrical greenish worms which under a lens are seen to be covered with short hairs. When the caterpillars are ready to change to chrysalids they spin a web of silk upon the supporting surface and just back of it, a loop of silk that serves to hold the chrysalis in place and keep it from swaying back and forth.

The chrysalids are characterized by having a pointed projection on the front of the head, the rest of the body being more or less angular.

Notwithstanding their close general resemblance to their food plants, the caterpillars of this family suffer from attack by various enemies.

Birds find many of them, not only eating them themselves but also using them freely for feeding the nestlings. Parasitic insects also take a heavy toll from these caterpillars. This attack of enemies is doubtless a chief reason why many of the common species are not much more destructive.

THE TRIBE OF THE WHITES

Three white b.u.t.terflies of approximately the same size are found widely distributed over the United States. The most abundant species is the White or Imported Cabbage b.u.t.terfly. The next in abundance is probably the Checkered White, and the rarest in most localities is the Gray-veined White which is a northern form.

=The White or Imported Cabbage b.u.t.terfly= _Pieris rapae_

There is probably no b.u.t.terfly which one can generally find so easily in its early stages as the White or Imported Cabbage b.u.t.terfly which is found practically wherever cabbages are grown and is generally so abundant that caterpillars and chrysalids are readily discovered. In the Northern states the insect pa.s.ses through the winter within the chrysalis, coming forth rather early in spring as the familiar white b.u.t.terfly with black dots upon the wings and blackish front angles of the fore wings. (_See plates, pages 64-65 and 81._)

The b.u.t.terflies that thus appear in spring flit freely about over fields, meadows, and gardens, sipping the nectar of various early flowers through their long, coiled tongues and stopping occasionally to alight upon the leaf of a cabbage or other plant of the mustard family to deposit the small, pale yellow eggs which remain attached by a sort of glue. The adult b.u.t.terflies continue their leisurely life for a fortnight or more, thus extending the laying of the eggs over a considerable period.

About a week after being deposited the egg hatches into a tiny green caterpillar that begins feeding upon the tender surface of the cabbage leaf. It is commonly called the cabbage worm and it is doubtless the most generally destructive insect affecting this crop. It continues to feed for several days before the first moult, after which it becomes decidedly larger and begins to eat again more voraciously than before.

It undergoes several successive moults during the next two or three weeks before it becomes full grown as a caterpillar. Unlike most b.u.t.terfly larvae it has changed very little in its general appearance during its growth. It is always of a pale green color, strikingly like the glaucous green of the cabbage leaf, a fact which doubtless helps to conceal it from the eager eyes of birds and other animals.

When the caterpillar is thus full fed it is likely to leave its food plant and find shelter elsewhere. Sometimes it will stop on the lower surface of the outer leaves, but more commonly it will find a piece of board, an overhanging stone, a fence-post, or the side of a building, where it will prepare for the change to the chrysalis. It will do this by spinning a silken thread upon the surface in which to entangle its hind legs and a loop of silk near by with which to hold its body. When these preparations are completed the insect will cast its last caterpillar skin, emerging as a grayish or brownish chrysalis, the color usually varying with the color of the surrounding surface.

A week or more later the chrysalis skin bursts open and the white b.u.t.terfly emerges to expand and dry its wings before it flies away for its leisurely life. There are two or more broods each season, the number varying with the lat.i.tude. There is a decided variation in the length of time required for the completion of the cycle from egg to b.u.t.terfly. In hot weather the insect may mature in about three weeks while in cooler weather it may require as much as five weeks.

_Its Introduction and Dispersal_

While it is well known that a large proportion of our most destructive insects have been imported from Europe, it is only in comparatively few cases that man has been able to make careful records of the times and places where the insects were introduced and to follow the spread of the pest from these original centres. The Imported Cabbage b.u.t.terfly is one of the few species of which this is true. This insect has been known for centuries in Europe, where it feeds freely upon the leaves of cabbages and turnips. So far as known it was first introduced into North America about 1860, when it appeared in Quebec.

Eight years later it was again introduced into the region of New York City. From these two points the insect spread gradually in various directions until in 1871 it covered the whole of New England and various parts of New York and New Jersey. From then on it spread even more rapidly and was evidently accidentally introduced into various parts of the country which became new centres of distribution. Of course it would be very easy for this to happen through the s.h.i.+pment of cabbages from one part of the country to another. Within thirty years of the time of its first introduction it had become a serious pest over practically all the United States and Canada.

The introduction and spread of such a pest is of interest in itself, but in this case there is to be noted the additional fact that the presence of this foreigner has practically led to the extinction of two native species of b.u.t.terflies, both closely related to each other and to the invader and both feeding upon the same plants. An almost pure white b.u.t.terfly--the Gray-veined White--was formerly exceedingly abundant in many of the Northern states, while farther south there was another species, the Checkered White, which was also abundant. Both of these have now so completely disappeared that in some localities they are almost never seen, while their imported relative has become perhaps the most abundant of all American b.u.t.terflies.

=The Gray-veined White= _Pieris napi_

One would naturally suppose that when a b.u.t.terfly was reduced to the greatest possible simplicity in its coloring there would be little chance for the development of geographical or seasonal varieties. But he would only have to study a large collection of specimens of this species, taken at different seasons and in different regions, to find his supposition at fault. Here is a b.u.t.terfly which is essentially a slender black-bodied creature with four white wings scarcely touched with color, and yet we are told that there are eleven varieties in the United States so distinct that they have received scientific names, not to mention various others which have been found in Europe. This is indeed a remarkable showing and it is a striking ill.u.s.tration of the infinite variations which Nature can produce with the most limited materials.

To me the seasonal variations of a b.u.t.terfly are always of greater interest than those which are geographical. We know that in the case of a great many animals, from insects to mammals, the different conditions of climate and physical environment found in different regions produce variations of many sorts. So it does not seem especially strange that in Alaska there should be a different form of a certain b.u.t.terfly than is found in Virginia. But that in the same locality there should be two or more forms of a b.u.t.terfly existing under identical conditions as to climate and environment is not so easily explained. In the case of the Gray-veined White we collect in early spring in New England, or other Northern states, a lot of chrysalids. We keep them until the b.u.t.terflies come forth and we find even here two distinct forms, one smaller and more delicate than the other, with both surfaces of the wings pure white: scientists call this form, _virginiensis_; the other larger with the under surface of the wings slightly tinted with yellow: scientists call this form _oleracea_. The first named has but one brood a year while the second lays eggs which develop into caterpillars that produce b.u.t.terflies of still a _third_ form, in which the upper surface of the wings is pure white with a slightly greater expanse: scientists call this form _cruciferarum_. These three varieties occur in Eastern regions and may be found in the same localities, and differ considerably from various geographical varieties found in the Far West.

The caterpillar of the Gray-veined White is a bit smaller than those of the nearly related forms, and in color is green with no distinct longitudinal markings, but with many fine dots of black over the surface. The cylindrical body is covered with a fine down. When feeding upon cabbage it is more likely to attack the outer than the inner leaves, and so even when abundant it is less troublesome to gardeners than the imported species. It is now, however, so rare that it seems to feed chiefly upon wild cruciferous plants and is more likely to be found along the borders of open woods than in gardens and fields. The winter is pa.s.sed in the chrysalis state.

=The Checkered White= _Pontia protodice_

Some years ago the Checkered White was commonly called the Southern Cabbage b.u.t.terfly but the general distribution of the imported species has had the same effect upon its abundance in the South that it has had upon the Gray-veined White in the North. Consequently, it is now much less abundant than formerly, even in the Southern states where it is most at home. There are two fairly distinct forms: the spring form and the summer form. The latter is practically of the same size as the Imported Cabbage b.u.t.terfly: the males have the hind wings nearly white above and the fore wings with a few black dots or spots upon their outer halves. The females are much more definitely marked, having the upper surface of both pairs of wings marked in black or brownish black in such a way as to enclose a large number of white diamonds. The spring form is decidedly smaller and the markings are much less distinct than in the summer form.

The seasonal history of this species is comparatively simple. In winter the chrysalids are found. From these chrysalids in early spring the small b.u.t.terflies of the spring form come forth. These lay eggs upon various cruciferous plants which hatch into greenish caterpillars that eat the leaves and soon mature so far as their caterpillar stage is concerned. They are then about an inch long, with downy cylindric bodies more or less marked with rather pale yellow stripes, touched here and there with purplish green or dotted slightly with fine black dots. These caterpillars now attach themselves by means of a b.u.t.ton of silk and a silken loop to some support like a piece of board, the side of a stone, or almost any available shelter. Each casts its larval skin and appears as a grayish chrysalis from which probably a fortnight later the summer form of the b.u.t.terfly emerges. There are commonly two broods of this summer form, making three sets of b.u.t.terflies for the entire season. The caterpillars of the second summer brood of b.u.t.terflies go into the chrysalis stage in autumn to remain throughout the winter.

Some very interesting observations upon the sleeping habits of this b.u.t.terfly have been made in St. Louis by Mr. and Mrs. Phil Rau. The insects were found abundantly resting upon the seed heads of white snakeroot. Early in October, when a warm south wind was blowing, the great majority of the b.u.t.terflies slept horizontally with their heads toward the wind. At other seasons and in other places, many of them were found in a vertical position but practically all had their bodies toward the wind prevailing at the time. The observers were unable to ascertain definitely whether the insects thus oriented themselves at the time of alighting, so that their wings presented the least resistance to the force of the wind, or whether this was a mechanical result of the breezes.

=The Great Southern White= _Pontia monuste_

There used to be in the Northern states before the advent of the Imported Cabbage b.u.t.terfly a familiar white b.u.t.terfly which then laid its eggs upon cabbages in much the same way that the imported pest now does. One who has seen this northern Gray-veined White and then sees the Great Southern White will be likely to think of the latter as a larger edition of the former, for in the males of the southern species the wings are practically white save for a narrow dusky border at the outer angle of the front pair, although in the female this dusky margin is wider and the hind wings show a series of dusky triangles near the margin. There is also a curious black marking suggestive of a crescent on each front wing near the middle of the front border, which helps to make the appearance of this b.u.t.terfly very distinct from that of any other.

Although this species is at times so abundant that it swarms in great flocks and although it has been known for many years, its life-history seems not to have been carefully worked out since it was first described by Abbott more than a century ago. The caterpillars feed upon cruciferous plants and when full grown are about an inch and a half long, of a general yellow color, more or less striped with purple lines. The species is distinctly tropical extending northward into our Southern states.

Dr. G. B. Longstaff reports this species as abundant in Jamaica where he found that the clubs of the antennae of the living insects showed a beautiful turquoise blue color, although another observer described them as bright green with a tinge of blue. This is an interesting color variation for a member of this group. In the tropics also there are two forms, one belonging to the dry season and one to the wet season.

_Synopsis of the Whites_

_Imported Cabbage b.u.t.terfly_ (_Pieris rapae_). Expanse 2 inches. Upper surface white with a black marginal dash on the front outer angle of the front wing. One round black spot on each of the four wings in the male. Two round spots on each of the front wings in the female and one round spot on each of the hind wings. Under surface of hind wings yellowish white; spots on front wings in same position as on upper surface. A spring form (_immaculata_) is smaller and the black spots are almost obsolete.

_Gray-veined White_ (_Pieris napi_). Expanse 2 inches. Upper surface white with only a darker marginal splash next the body. Under surface white with gray veins.

_Checkered White_ (_Pontia protodice_ or _Pieris protodice_). Expanse 2 inches. Upper surface white, strongly marked especially in the female with dark grayish brown on both pairs of wings. Along the outer margins these marks are so arranged as to enclose white diamond spots.

Male with front wings only lightly marked and hind wings scarcely marked at all. Under surface much like upper, with a slight yellowish tinge in female.

_Great Southern White_ (_Pontia monuste_ or _Pieris phileta_.) Expanse 2 1/2 inches. General color white with a narrow black margin around apical angle of front wings. These margins are wider in the female, in which s.e.x there is a series of marginal spots on the hind wings.

Easily known by its large size.

THE TRIBE OF THE ORANGE-TIPS

When one sees a gossamer-winged b.u.t.terfly flitting from flower to flower on a bright June day it seems one of the most ethereal of earth's visions. One could readily fancy that the whole sight--flowers, b.u.t.terflies, and all--might easily vanish into thin air. So it is something of a shock to hear scientists talk about fossil b.u.t.terflies and to realize that these fragile creatures have been living generation after generation for untold millions of years.

A realization of this fact, however, helps us to understand the many wonderful ways in which b.u.t.terflies in all stages of their existence have become adapted to the conditions of their lives.

There is perhaps no group of b.u.t.terflies whose beauty seems more fragile than that of the Orange-tips. These are delicate creatures, with slender bodies and almost gauzy wings, of a size somewhat smaller than our common white and yellow b.u.t.terflies. Perhaps the most remarkable feature is the marking of the wings, the upper sides of the front pair having an orange patch near the apex and the under sides having a background of delicate whitish or yellowish green, lined and spotted with darker coloring in a very characteristic way. This peculiar marking is so significant that it has been called "flower picturing." To understand the reason for its existence one has only to watch the b.u.t.terflies in their native haunts. He will find them flitting from blossom to blossom among the plants of the mustard family--the _Cruciferae_. This is one of the most characteristic families in the plant world: the foliage for the most part is small and delicate and the flowers have a characteristic four-petaled structure, being practically always of small size and generally toned in whites or yellows. When an Orange-tip is at rest upon these blossoms it merges so completely into the background that it disappears from view. Should a bird chase one of these insects through the air it would see chiefly the orange tips which are so marked upon the upper side of the wing, and when the b.u.t.terfly closed its wings and lighted among the flowers the orange color would instantly disappear and there would be only an almost invisible surface against the background of flower and leaf.

The adaptations of these Orange-tips to the conditions of their lives are by no means confined to this remarkable resemblance to the flowery background. In the case of some species the whole yearly cycle has been adapted to correspond to the yearly history of the cruciferous food plant. As is well known many species of the mustard family spring up early in the season, put forth their blossoms which quickly develop into fruits and then die down, the species being carried through until the next year by the dormant seeds. In a similar way the Orange-tips feed as caterpillars upon the host plant through the spring, completing their growth before the plant dies and then changing to chrysalids which remain dormant through summer, fall, and winter and come forth as b.u.t.terflies early the following spring. The insect has thus adapted itself in a most remarkable manner to the yearly history of its plant host.

=The Falcate Orange-tip= _Synchloe genutia_

The Falcate Orange-tip is about the only member of this tribe generally distributed east of the Rocky Mountains. This is a beautiful insect which is sparingly found even as far north as New England. It is more abundant throughout the Southern states, occurring south at least as far as Texas. It appears to be a good ill.u.s.tration of the adaptation of its development to that of its food plants. The eggs are laid upon leaves or stems of such spring-flowering _Cruciferae_ as rock cress (_Arabis_), and hedge mustard (_Sisymbrium_). On hatching the caterpillars feed upon stems, leaves, flowers, and even seed pods of these plants, becoming mature in a few weeks and changing to chrysalids under the protection of such shelter as they can find. In the Northern states these chrysalids remain unchanged until the following spring when the b.u.t.terflies emerge and are found upon the wing for a few weeks in May and early June. In some southern regions at least the species is evidently double-brooded, as Dr. Holland reports that he has taken the b.u.t.terflies in late autumn in the western portion of North Carolina.

[Ill.u.s.tration: Egg of _Synchloe genutia_, magnified 20 diameters. (From Holland)]

This Falcate Orange-tip is one of the daintiest and most exquisite of northern b.u.t.terflies. It is a prize which any collector will find joy in possessing. It is easily recognized by its general white color, which in the female is relieved only by a distinct black mark on the upper surface of the front wings and a row of marginal markings upon all the wings. The male is slightly smaller and is at once known by the orange blotch on the outer angle of the upper surface of the front wing. This outer angle projects into a distinct point which gives the species its name Falcate. (_See plate, page 256._)

Dr. J. L. Hanc.o.c.k has described in a most interesting manner the way in which this Orange-tip loses itself among the flowers of rock cress.

In northern Indiana he found this b.u.t.terfly abundant in April at the time of the blossoming of _Arabis lyrata_. The b.u.t.terflies would be flying about, easily seen in the air. Then they would suddenly disappear and could be found only after the most careful search. They had simply lit upon the flower heads, when the flower picturing of the under surface of the wings blended perfectly with the appearance of the cl.u.s.tered flower.

"The green markings of the under side of the wing," writes Dr.

Hanc.o.c.k, "are so arranged as to divide the ground color into patches of white, which blend with or simulate perfectly the petals of the cl.u.s.tered flowers. The eyes of the b.u.t.terfly are delicate pale green and the antennae are whitish, all of which adds to the effectiveness of the blend. The flowers of _Arabis_ have white petals with the centre yellowish green, as is also the calyx. There is a shade of pink outside the base of the petals. All in all, the adaptation of insect to flower here displayed is one of rare exquisiteness."[C]