HONEY-PRODUCING CATERPILLARS.
Late in June, growing abundantly in the edges of woods throughout this region, may be seen the Cimicifuga racemosa of botanists, popularly called Rattleweed, or Black Snakeroot. It sends up a stalk, sometimes branching, four or five feet, terminating in a spike or spikes, six to ten inches long, of round, greenish-white buds, which stand upon short stems, and are arranged in rows about the stalk, diminishing in size till they reach the pointed top. The lower buds, when they are about the size of an ordinary pea, open first, and the flowering proceeds by degrees up the spike, so that buds are to be met with throughout a period of from four to six weeks. The flowers emit an intensely sweet odor, which renders them attractive to butterflies and bees.
But should you examine these buds with care, you will find a number of small caterpillars, the larva of the beautiful Azure Butterfly, called Lycæna pseudargiolus, feeding thereon. During its younger stages it is white, and so near the color of these buds that it is well protected, and very difficult to find. Later on, it may be white or greenish, and often diversified with a few black or brown patches, irregularly diffused over the surface.
When mature the larva is one-half of an inch in length, and, like all Lycænid larvæ, is onisciform, or shaped like the little pill-bug, so common under stones and logs. The head is very small, and is placed on the end of a long, green neck, which at the junction is of the thickness of the head, but gradually enlarges, and seems to be fixed at the hinder part of the second segment, the latter being hollowed out so as to form for it a sheath. In the final larval stages this segment is elevated, transversely compressed, and inclines forward, thereby shielding the head as the larva moves about. When quiescent the neck and head are wholly retracted, and as the former, when fully extended, is very much longer than the depth of the second segment, it must possess considerable elasticity.
The larva feeds on the heart of the bud, and to reach this cuts away the surface on one side till an opening is made sufficiently large to admit its head; and as it feeds the second segment is firmly pressed against the bud so as to permit the utmost elongation of the neck. Thus it is enabled to eat out the contents of the bud, and only desists when there remains but the empty shell. When so engaged the anterior segments are curved up and the others rest upon the stalk of the plant, but very small larvæ repose wholly in the bud. Not a single instance has been observed where an open flower has been attacked, but the destruction of buds is very extensive.
But now comes the most remarkable part of the larval history of Pseudargiolus. The whole upper part of the larva is covered with small, glassy, star-shaped processes, scarcely raised above the surrounding surface, from the centre of which spring short, filamentous bodies, bristling with feathery-looking tentacles, which the caterpillar has the power of protruding at will. It throws them out like the tentacles of Papilio or the horns of snails. More singular still is an opening upon the eleventh segment, placed transversely and surrounded by a raised cushion, about which the granulations that cover the body of the caterpillar are particularly dense. From the middle of this opening, which is shaped like a button-hole, issues, at the caterpillar’s will, a sort of transparent, hemispherical vesicle, from which is emitted a good-sized drop of fluid, which the animal is capable of reproducing when absorbed.
PSEUDARGIOLUS BUTTERFLY.
Larva Feeding on Bud of Black Snakeroot, and Guarded by Ants.
Four species of ants may be seen attending, not the small larvæ, but those that have attained the nearly mature condition. They are invariably found on or near the larva. Their actions, as they run over the body, caressing with antennæ, evidently persuading the larva to emit a drop of the fluid, are alike curious and interesting. Most of this caressing is done about the anterior segments, and while the ants are thus occupied, or rather, while they are absent from the last segments, the tubes of the twelfth seem expanded to their full extent, and so remain, without retracting or throbbing, until the ants come hurrying along with great excitement and set foot or antenna directly on or close by the tubes, when they are instantly withdrawn. The ants pay no heed to the tubes. They seek for nothing from them, and expect nothing. But they turn at once to the eleventh, caress the back of that segment, and, putting their mouths to its opening, exhibit an eager desire and expectancy. Suddenly a dull green, fleshy, mammilloid organ protrudes, and from the summit of which comes a tiny drop of clear green fluid, which the ants, some two or three perhaps standing about it, lap greedily up. As the drop disappears, this organ sinks in at the apex, and is so withdrawn. The ants then run about, some in quest of other larvæ upon the same stem, some with no definite object, but presently return and pursue the caressings as before. The intervals between the appearance of the globule vary with the condition of the larva. Where exhaustion by long-continued solicitings occurs, some minutes elapse before renewal is effected, the tubes in the meantime remaining concealed. Fresh larvæ, however, require little or no urging, and globule follows globule, as many as six emissions in seventy-five seconds, without even a retracting of the organ. Often the presence of the ant, when the larva is aware of it, evokes, all unsought, the sugary fluid.
Ordinarily the tubes expand when the ants are absent from the last segments, and are certainly withdrawn when they come near. These tubes, from all appearances, serve as signals to the ants. When the latter discover them expanded, they know that a refection is ready, and rush to the opening in the eleventh segment where it is to be found. The tubes certainly serve no other purpose. No visible duct appears in the dome of the tube when largely magnified, and the ants seek nothing from it or the twelfth segment. They cannot be used to intimidate, or to frighten away enemies, for in the younger stages, when the larvæ have the most to dread, neither the tube nor the organ in the eleventh segment is available. The outward openings, and the orifice in the eleventh segment, exist in the youngest larval stages, but are functionless until the larva has nearly attained maturity. Ants seldom attempt to caress or solicit young larvæ, but pass them by with indifference, seemingly knowing that they cannot emit the secretion. When an ant approaches one of these immature larvæ, the larva manifests considerable annoyance, throwing up the hinder segments, as though the ant was an enemy which it was desirous to get rid of. If the tubes could now be thrust out, the ant would be attracted, rather than repelled.
But when the period arrives that the tubes are free, and the secretion is ready to be ejected, which is perhaps just after the third skin-moulting, and it cannot be earlier, the larva grows now quiet and submissive, inviting the attentions of the ants, and rewarding their antennal caresses.
Four species of parasites affect these larvæ. Two are dipterous. These, which are of the size of the common house-fly, deposit their eggs, during the second larval stage, on the back, and near the junction of the second and third segments. In process of time the grubs hatch and eat their way into the larva, to emerge when the latter has become fully grown, thus destroying its life. Another of these enemies is a minute hymenopterous insect, whose egg is placed in the very young larva, probably in the first stage of its life. The grub, in this case, eats its way out of the half-grown larva, spins a silken cocoon, from which in a few days issues the newly-matured parasite. The destruction of larvæ by these, and very likely by other similar parasites, is doubtless immense. But no parasite attacks, it does seem, the mature larva, for, if it did, the grub of the former would live within and destroy the chrysalis, and instead of a butterfly emerging therefrom would come forth the parasite. Multitudes of chrysalids of other species of butterflies are thus destroyed, but Pseudargiolus, at this stage, appears to enjoy a singular immunity from enemies.
Why this species, and doubtless many others of its family, are thus favored, will soon be apparent. Ants may be seen wherever these larvæ may be found, ever ready to receive the honeyed secretion when it pleases the little creatures to eject it, but all the while exercising the closest vigilance lest some wary ichneumon may come along and deal a thrust of its ovipositor, which means misery and ultimate death to their helpless friends. So intent is the larva, with its head buried in the flower, upon its feeding, and so quietly and stealthily does the ichneumon approach its intended victim, that hardly a single individual would be left to tell the story of its existence were it not for the ants. The larvæ know their protectors, it would seem from their actions, and are able and willing to reward their services. The advantage is mutual, and the association friendly. No compelling by rough means on the one part is noticeable, and no reluctant yielding on the other. All demonstrations made by the ants are of the most gentle character. They caress, entreat, and as they drink in the sweet fluid, lifting their heads to prolong the swallowing, they manifest to the utmost their satisfaction and delight. It is amusing to see them lick away the last trace, caressing the back of the segment with their antennæ as they do so, as though they were coaxing for a little more.
In Pseudargiolus the tubes are white, cylindrical, nearly equal in size, rounded at summit, and studded with little tuberculations from which arise the tentacles. These last are tapering, armed with small spurs set in whorls, and stand out straight, making a white hemispherical dome over the cylinder, but none of them fall below the plane of the base of the dome, nor do they ever hang limp or lie across the dome, as is the case in a European species. When the tube comes up the rays rise in a close pencil, and take position as the dome expands; but, on the contrary, when the tube is withdrawn, the top of the dome sinks first, the rays coming together in pencil again.
VIOLACEA BUTTERFLY.
Larva, Protected by Ants, Feeding on Flower-buds of Dogwood.
Lycæna pseudargiolus is subject to great variation, and occurs under many forms, most of which having been regarded as distinct species. In the early spring Violacea appears, and is characterized by dimorphism in the female, some of that sex being blue, others black. This form, which may be called the winter form, deposits its eggs in the clusters of flower-buds of the Dogwood, the young larvæ obtaining their first food by boring into the buds, but later on eating their way into the ovaries. The flies that come from these larvæ late in May are Pseudargiolus, which, as stated before, lays its eggs on Cimicifuga racemosa, most of the resulting butterflies over-wintering to produce Violacea. A small percentage of the May chrysalids give butterflies as late as September, which are smaller than the parent-form, and also differ therefrom in the more decided character of the marginal crescent discal spots on the under side of the wings. There does not seem to be any regular second summer brood, that is, there are but two regular annual broods, the Violacea of March and the Pseudargiolus of May, the individuals happening to emerge in July, August and September being irregular visitants, for which the name of Neglecta has been given. The females of the last form lay their eggs upon Actinomeris squarrosa, and the chrysalids, thence resulting, give Violacea the next spring.
Larvæ feeding on Dogwood vary much in color from those that feed on the Black Snakeroot, few being white in the last stages, but nearly all dull-crimson or green, or a mingling of the two. Nevertheless, a small percentage of the larvæ on Cimicifuga racemosa are also green or crimson, though the most of them white. Ants do not seem to visit the larvæ on the Dogwood, and on being introduced to them in confinement treat them with indifference. On rare occasions tubes have been discovered in the eleventh segment, fully expanded, and accompanied by a pulsating movement, but no teasing or irritating availed to make them appear. Even severe pressure applied to the sides of the segment failed to force out any fluid. As with the fall food-plant, Actinomeris squarrosa, the Dogwood is neither sweet nor juicy, and it is possible that the larvæ feeding on these plants do not secrete the fluid.
Eggs of this polymorphic species are round, flat at base, the top flattened and depressed, and have a diameter of one-fiftieth of an inch. Their ground-color is a delicate green, the entire surface being covered with a white lace-work, the meshes of which being mostly lozenge-shaped, with a short rounded process at each angle. In from four to eight days the egg hatches into a larva, which is scarcely one-twenty-fifth of an inch long, and whose upper side is rounded, the under being flat. On each side of the dorsal line is a row of white clubbed hairs, with similar ones at the base and in front of the second joint, making a fringe around the body. The head is very small, obovoid, retractile and black; the legs retractile, and the color a greenish-white or brownish-yellow.
The first moult occurs in from three to five days, the larva having increased to twice its former length, while very little difference is manifest in the coloration. In from three to five days the caterpillar has again changed its skin, doubled its length, assumed more pronounced colors, which are diversified in some with mottlings upon back and sides, and developed along the back, from the third to the tenth joint, a low, broad, continuous, tuberculous ridge, cleft to the body at the junction of the segments, the anterior edge of each joint being depressed, the sides incurved. The third moult takes place in three or four days more, but there is very little change from the former period. Three or four days subsequent to this change occurs the fourth or final moult, and in five or six days from this the larva is ready to pass into the chrysalis state.
In its mature form the larva is about one-half of an inch in length. The body is onisciform, flattened at base, furnished with retractile legs, and has the back elevated into a rounded ridge, which slopes backwards from the sixth segment. The sides are rather deeply hollowed, and in the middle of each segment, from the third to the eleventh, is a vertical, narrow depression. The last segments are flattened, the last of all terminating roundly, its sides being narrowed and slightly incurved, while the second segment is flattened, arched and bent nearly flat over the head. Standing on the body is a ridge, tubercular in nature, which in each segment from the third to the eleventh is distinct and cleft to the body. In color, specimens vary. Some examples are white, others decidedly greenish, but many have the posterior slope of the second segment black or dark brown, while a few have most of the back a dark brown, irregularly mottling a light ground, or with small brown patches diffused over the back, but mostly on the anterior segments. The entire surface is velvety. This appearance is caused by minute stellate glossy processes, scarcely raised above the surface, mostly six-rayed, and sending from the centre a concolored filamentous spine a little longer than the rays. These stars are arranged in nearly regular rows, and are light, except in the brown patches, where both star and spine are brown. This velvet-like condition of the skin only reveals its true composition under a magnifying glass.
On the eleventh segment, near the posterior edge of the back, is a transverse slit, in a sub-oval spot, from which proceeds a membranous process; and on the twelfth, on each side, is a mark like a stigma, but a little larger, from which proceeds a membranous tube, ending in a crown of feathery tentacles, these three special organs being exposed or concealed at the will of the larva. The head is small, obovoid, dark brown, and is placed at the end of a long, pale green, conical neck, which is rectractile, both neck and head being covered by the second segment.
Before changing to a chrysalis, the summer larvæ sometimes turn pink, and from pink to brown, or become brown without the pink stage, although others remain white or change to rusty brown. The body contracts to about three-tenths of an inch and takes on a rounded form.
The chrysalis is dark-brown or yellow-brown, but varying in color, the wing-cases being dark or green-tinted. Two sub-dorsal rows of blackish dots are found on the abdomen, and sometimes a dark dorsal line. In the few instances in which the butterfly emerges the same season the duration of this stage is from thirty to sixty days, but most chrysalids pass the winter and mature in the spring.
NEGLECTA BUTTERFLY.
Larva Feeding on Central Florets of Actinomeris, and Guarded by Ants.
Now for a description of the butterfly. In general terms, the upper side of the wings of the male is a deep azure-blue, with a delicate terminal black border. On the apical part of the fore-wings the fringes are black, but white and barred with black on the rest of these wings and on the hind-wings. In the female the fore-wings have a broad, blackish outer border, in some examples extending along the costa, while the hind-wings have a blackish costa and a row of dark spots along the outer margin. Usually the ground-color is a lighter blue in the females than in the males. A pale silvery gray, with a silky lustre, is the color of the under side of the wings, which is relieved by a row of spots along the outer margin, each preceded by a crescent, a curved row of elongate spots across the disk of the fore-wings, and several spots on the basal part of the hind-wings, all the markings being of a pale brown color. Violacea, the so-called winter form, has the dark parts and crescents on the under side of the wings quite prominent, but they do not, either in the outer border or in the basal portion, coalesce. Pseudargiolus, the largest of the series, there being but three forms in Pennsylvania, expands one and four-tenths inches. The upper surface of the male usually has a terminal border to the hind-wings of the same shade of blue as is visible on the fore-wings, the middle area of the hind-wings being a little paler than this border on the fore-wings. On the under side of the wings the spots are much smaller than on the preceding form. Neglecta, which resembles Pseudargiolus, and has the spots on the under surface small, is a smaller form, never expanding more than one and one-tenth inches. It is a summer form when there is more than one generation in a season, ranging from Canada, through New England to West Virginia and Georgia, and occurring also in Montana and Nevada. Violacea has a more extended limit, being found in Alaska, British America, Ontario, Quebec, New England to West Virginia, and Colorado, while Pseudargiolus ranges from Wisconsin south to Tennessee, and on the east from Pennsylvania to Georgia.