Popular Science Monthly/Volume 34/December 1888/The Pine-Tree Lizard
|THE PINE-TREE LIZARD.|
ON the outskirts of the quaint little village of May's Landing, N. J., there is seen that rare object, an abandoned railroad. Starting near this place, and running eastward for a distance of some six miles, is a single track, laid upon a substantial road-bed of gravel, and extending through typical Jersey pine-barrens and cedar-swamps. For several years not a car has passed over the rails, which, left to nature, have grown nutty-brown with rust, and often concealed by luxuriant growths of false ipecac (Euphorbia ipecacuanhæ), great circular mats of deep purple or pale-green foliage, for such is the freak of the plant to vary thus in color.
When I visited this spot late in May, 1887, the charm of the abandoned railroad was rivaled by the beauties of the surroundings. The glistening snow-white sands were thickly starred with golden Hudsonia; the creek's banks, weighted with densest foliage, brilliant with sarracenia in the height of its glory, and everywhere the more modest grasses gave way to sparkling sun-dews. One knew not where to turn, so crowded were the spot's enticing features, and the rambler was likely to return empty-handed, as is so apt to be the case where attractions are spread out in bewildering profusion. Wondering what novelties might be in store as I passed the outlying traces of the village, I soon found my progress suddenly and effectually stayed—I had reached the tottering, crumbling trestle over Babcock's Creek. Here the gray lizards found a most congenial home, and the peculiar locality offered every reasonable facility for studying them. A long-desired opportunity was at last mine, and birds and botany were no longer thought of.
This pretty creature, known as the gray or pine-tree lizard (Sceleporus undulatus), is also, in many localities, called the "brown swift"; and this seems a most appropriate name, as we read the remarks of Holbrook, De Kay, and of Alexander Wilson, on the habits of the creature. For instance, the last named, in his "Ornithology," expresses surprise that a sharp-shinned hawk should have captured one, "as lightning itself seems scarce more fleet than this little reptile." I was not prepared, therefore, to find the "swifts" on the trestle anything hut swift. It was by hiding, and not through speed, that they sought to escape, and it proved comparatively easy to capture them with the unaided hand. Often they played bo-peep merely around the timbers, and were readily surprised, so that they ran into one hand as they avoided the other. This proved to be the case, also, when I searched for the lizards in the pine-woods, which were as readily captured when up on trees as were those on the trestle.
The village boys adopted ordinarily the simple plan of using a thread-noose placed at the end of a short stick. Dropping the noose gently about the neck of the lizard, they lifted the creature slightly, when its struggles at once tightened the thread and made it a prisoner. It was a favorite pet with the children, and, when I asked some of them if it ever bit or snapped at their fingers, they were greatly amused. I lay stress upon this point, because of the rather widely spread opinion that these lizards are venomous. It is one with the equally absurd impression, due to ignorance and belittling prejudice, that all our snakes are harmful; but a curious feature in this case is the fact that the impression of the lizard being venomous obtains in inverse ratio to the abundance of the animal. Where exceedingly rare, the lizard is dreaded; while, where abundant, as at May's Landing, it is a favorite pet with the children.
Probably a closer study of animal life would materially reduce the list of species supposed to be harmful by those who see but little and know absolutely nothing about them, and put an effectual check upon those who, taking advantage of the ignorance of their audiences, assert deliberate falsehoods, because more entertaining than the simple truth.
As is well known, the pine-tree lizard is quite sensitive to low temperatures. It does not make its appearance in southern New Jersey earlier than May, nor remain abroad later than September. Of course, this is a general statement, and only approximately true, as all such statements must be. Perhaps there can be found nothing more absurd in scientific literature than the frequent ex-cathedra statements—for instance, concerning the movements and range of our birds, as though the latter recognized any other law than that of their own convenience and fancy.
At May's Landing I found the lizards sensitive even to the ordinary variations of temperature of average summer days, observing that, whenever it was cloudy, they were far less abundant, and actually sluggish. On the other hand, the extreme degree of heat to which they are willing to expose themselves is not a very high one, judging from the actions of a large number kept in confinement.
Fifteen adult lizards were placed in an inclosure in which every prominent feature of their homes was reproduced. I found that at 120° Fahr., with the atmosphere perfectly still, they invariably sought shelter, clustering in one cooler and dark corner; but at 100° they were exceedingly active, particularly if hungry, and made no effort to avoid the direct rays of the sun.
When exposed to a sudden transition from a very high to a low temperature, they quickly became inert, and, as the warmth was allowed to increase, it was instructive to see the sluggish movements of both the lizards and the imprisoned flies give way to more active ones, which culminated in the restored suppleness of the reptiles being equal to the capture of the swiftly darting insects. Forced exposure, for a period of three hours, to a temperature of 135°, caused death in four instances, and brought about a condition akin to æstivation in nine specimens thus exposed. As the pine-tree lizards are always found in localities where there is adequate shelter from excessively high temperature, it is not probable that æstivation ever occurs, as it does occasionally among some of our wild mice; but it is interesting to note that a condition closely allied to it can be artificially produced.
The conclusion reached by both field observation and experiments was, in brief, that when the temperature is such that those forms of insect life upon which they depend become inactive, the lizards withdraw to their shelters and likewise remain quiet if not asleep, this period of inactivity extending over several days, as during the prevalence of a northeast storm, or a protracted "spell" of cool and cloudy weather. Again, experiments with a large number in confinement showed that when kept without food at a low temperature, they lived for many days, while a like number starved in a short time when a high temperature was maintained. This lizard, therefore, appears to be one originally belonging to a tropical climate, that has gradually become adapted to a temperate and variable one.
The normal coloring of the pine-tree lizard is distinctly protective. Whether this has been gradually acquired or not, it is certain that it now renders the animal quite inconspicuous. Particularly when it is resting upon a rough-barked tree is this true; and one of my first objects, in studying the species in its native haunts, was to determine how far the markings were changeable and under their owner's control. Many specimens were found to be quite dark—indeed, almost black—while others were so light that the undulating transverse bars upon the back were very distinct and discernible at a considerable distance. This difference, I am quite sure, bore no relation to the surroundings; and the specimens subsequently collected and kept under daily observation for nine weeks practically retained the light or dark coloring they possessed, at the time of capture. In confinement many individuals remained of a light color under all circumstances; others, that were dark when received, became light for brief periods, but were very dark fully ninety-five per cent of the time they were under observation.
The long and broad glistening green markings upon each side of the abdomen are equally variable, certainly not a distinction of sex, as suggested by Le Conte and Say, and often absent for weeks in specimens which occasionally exhibited them in all their brilliancy.
In no instance was there that prompt change of hue that we see in the tree-toad (Hyla versicolor), and even more so in the wood-frog (Rana sylvatica). The change in the latter is as abrupt and complete as in certain fishes, and is particularly significant, inasmuch as it is the only frog that needs protective coloring, living as it does in woodland tracts, where it is exposed to an abundance of enemies: and may it not be that, by its power to adapt itself to the general color of the surroundings, it renders itself inconspicuous to the insects upon which it preys? If so, the control over its color becomes doubly advantageous.
Vision in the pine-tree lizard is apparently not very acute, although the eyes are exceedingly bright, and, when coupled with certain movements of the head, suggest considerable intelligence. It was found very difficult to test their visual powers, although, once captured, these lizards became extremely tame, patient, and obedient, and I could only infer that the sense of sight was none of the best from the fact that when held to a mosquito-frame in a window, upon which house-flies were walking, they missed fully one half of those at which they snapped; and other lizards in confinement, but where every possible freedom of movement was practicable, often made many attempts to capture flies before success crowned their efforts. If, therefore, when at large, they depended principally upon winged insects for subsistence, their lives would indeed be laborious ones; but insects of sluggish movements, ants, and small spiders, are all freely partaken of. My friend Mr. George Pine, of Trenton, N. J., a very careful observer, assures me that of the two insects, house-flies and Croton-bugs, his lizards certainly preferred the latter, but were not particularly expert in capturing them. And now, assuming that the eye-sight of these little reptiles is not highly developed, what of the curious "pineal eye" which they possess? Prof. Macloskie has recently announced in "Science" that it "is so well developed ... that it may probably seem to warn its owner of the advent of daylight. It is a lenticular, glassy area of the skin of the vertex (about a millimetre in sagittal diameter), surrounded by a yellow border, and having a dark spot in its center. The dark spot is opaque, caused by a mass of pigment internal to the dermis, set on the extremity of a pineal outgrowth from the brain. The clear area around it is caused by the dermis, which is transparent and free from the pigment which covers it internally in other parts. The eye is covered by an escutcheon-shaped epidermal shield, more transparent in the center and larger (three by three millimetres) than the normal epidermal scales. The only sign of degeneracy is the central cloudy mass of pigment, like a big cataract."
I was naturally desirous of determining for myself how far it was sensitive to light, but found the investigation beset with difficulties. Chloroformed lizards that were deprived of their eyes, although the amputation was dexterously performed, did not revive sufficiently to make their subsequent movements suggestive; or did sympathetic ophthalmia set in and affect the pineal eye?
I subsequently hit upon a plan, using very thin India-rubber cloth, by which the eyes proper were effectually closed, and the "eye" of the vertex left free. The lizards thus provided with a blinding head-gear were separated from their fellows and placed in a roomy inclosure, made up of several almost dark and very light alternate sections, the temperature being even throughout the lizards' range. The arrangement was, perhaps, too artificial for a satisfactory series of observations, but it became evident at once that the lizards recognized the difference between the dark and light areas, and their prompt return to the latter when removed from them, and again their actions when they returned, all showed the appreciation of a difference, which I know was not one of temperature, but beyond this I could determine nothing; but I recalled, at this juncture, the significant fact that in the woods about May's Landing I noticed many lizards buried in the fine sand and leaf-mold, their eyes closed and covered, but the top of the head and a portion of the back, for its whole length, exposed. The same was subsequently noted as a position frequently assumed by the lizards in my Wardian cases. If, therefore, the "pineal eye" is sensitive to light, it is still of some use to the creature, as it would certainly respond to a passing shadow, and so warn the animal of the approach of a possible enemy. It certainly would be greatly to the lizard's advantage if it had a perfect eye in the top of its head, especially when it rests upon the trunks of trees, and is exposed to the attacks of predatory birds; but the "pineal eye" is at most but a remote approach to this. On the other hand, it was found that whenever I converged the rays of light with a burning-glass, always so suddenly that no thermal effect was produced, there was caused a movement of uneasiness, a flinching, on the part of the lizard that was extremely suggestive.
The most superficial examination of the external ear of the pine-tree lizard will at once lead one to infer that the animal's hearing is acute; and this is true. When watching the lizards on the trestle over Babcock's Creek, at May's Landing, I was forcibly struck with this fact. Such of them as were basking on the timbers of the bridge were not disturbed when I approached them with moderate care, stepping only on the cross-ties, or between them; but if I struck the rails with my cane they instantly took notice of it and assumed a listening attitude. I subsequently experimented upon this point, and found that when my companion struck the rails a smart blow, even at a distance of fifty yards, the lizards were aware of the peculiar sound, and acted accordingly, even darting out of sight with that swiftness that characterizes their first few steps. I have recently learned from Rev. John E. Peters, Sc. D., of May's Landing, that his observations lead him to conclude that the sense of hearing is not very acute, and that they depend principally upon that of sight for safety and the finding of their food; but his experiments were not so extended as my own, and limited too largely to specimens in confinement.
It is a most interesting fact, although so very wild when first met with, that, once captured, they instantly become tame. Indeed, I have had them lie quietly upon my hand, while walking in the woods, and make no effort to escape. There is a bare possibility that the efforts on their part to escape, and fear, when finally captured, may produce a hypnotic condition, or something like it, but this would pass by and leave them wild. This, I think, never occurs. Once in my hand, I have never known a pine-tree lizard to be otherwise than perfectly tame. But, in a large series in confinement, I found that the sense of hearing was constantly brought into play, as shown by their ludicrous actions when flies, shut in a thin paper box, were placed near them. They not only heard but recognized the noise—a very important matter, bearing as it does upon their intelligence. Indeed, in the woods about May's Landing I found that the lizards were perfectly familiar with many sudden sounds and paid no attention whatever to them. Some of these were the sonorous croak of the bull-frog, the quick scream of the blue-jay, the rattle of the golden-winged woodpecker, and the coarse cry of the great-crested fly-catcher. These were all unheeded, while my own coughing, the whistling of a single note, or the loud utterance of a word, caused them either to assume a make-ready attitude or to dart away. On the other hand, have these lizards any voice? Their actions inter se are strongly suggestive of the affirmative, but, so far as I am able to determine, their utterances are confined to hissing, and this I only heard when I provoked the creatures by the sudden infliction of severe pain. Among a large number, in nine weeks I never heard a voluntary hiss. This, however, is wholly negative evidence, and I am disposed to believe that an animal possesses a voice, if its habits, in their entirety, suggest that it has one. This perhaps unscientific method of reasoning arises, on my part, from the fact of having long suspected that certain fishes and salamanders had voices, before they were detected—my suspicions being based upon the habits, as a whole, of these creatures. Certain snakes, too, that are now thought only to hiss, will, I believe, be found to have a limited range of scarcely audible utterances: so with the pine-tree lizards. I certainly have no reason to believe they talk, but possibly they may whisper in each other's ears.
Upon several occasions I sat, unseen by them, for a long time, very near my pen of lizards, and listened attentively, hoping to catch some sound that was clearly a voluntary utterance of a lizard. I only determined that one's ears, under such circumstances, become highly supersensitive, and a great deal is heard at a time when, in fact, positive silence prevails. Generally, the lizards were perfectly quiet, but at times one would move, and then a general scuffling ensued; but how far the noises were attributable to their activity I can not say; probably entirely so. The faint, snake-like hiss, that has fairly to be squeezed out of them, is the range of their vocal utterances, so far as I yet know.
Concerning the breeding habits of this creature, I had no positive knowledge prior to my visit to the pine-barren regions of southern New Jersey. I had heard the statement made that the eggs were small, quite numerous, and deposited on the under side of prostrate logs, and even in loose wood-piles that were constantly disturbed, and that the eggs were not concealed or protected in any way. All this I knew to be false; but where were the eggs of the pine-tree lizard placed? Questioning observing residents of localities where the species abounded, I was invariably informed that the eggs were laid in sand, in pits dug by the lizards and carefully covered up. They were only discovered by accident, no trace of their presence being noticeable. Further, that after heavy showers the eggs were sometimes exposed, and in this way a check was put upon the increase of the animal's numbers. Of course, solar heat alone was relied upon to mature the eggs. Recently, Rev. Dr. Peters has informed me that the eggs "are said to be laid in bunches," but just what is meant by being "bunched" I am at a loss to understand. They certainly are not attached to each other by any agglutinating substance. At least, the female lizards in my pens laid only dry, free eggs, which they deposited in conical pits, one egg, the lowermost, being in the bottom, then three above it, and four in the third tier. Such was the position in two sets of eggs, while the others were scattered over the sand in bewildering confusion. None of these hatched, the failure to do so, inasmuch as they were fertile, being due, I believe, to the surroundings being too dry. Probably a certain amount of decaying vegetable matter is mingled with the sand when the eggs are laid, and thus a moist heat is produced, which is as necessary as it is in the case of the eggs of the alligators and crocodiles.
The ova laid by my penned lizards were long, narrow, covered with a tough skin, free from calcareous matter, and varied in weight from twenty to twenty-four grains. At May's Landing, I am told, the eggs are usually laid about June 1st, and hatch about July 10th.
While the abandonment of their eggs in this apparently heartless manner leads to the supposition that they are indifferent to their offsprings' welfare, which is true, it is somewhat interesting to notice how very tolerant they are of the petty annoyances to which their own or another's young subject them. My observations on this point were made from a number of young and old confined in a roomy Wardian case, but probably what I there saw holds good among the lizards in their native haunts. I am sure it did among the many living on the old trestle at May's Landing. Often a little lizard, and sometimes two, would perch upon the head and back of an adult, and there be allowed to sit for fully an hour. The sharp claws of these youngsters seemed at times dangerously near the eyes and ears of the patient old one, but it offered no resistance, and, when I forced such burdened lizards to move, it was always with a deliberateness that suggested that they were really averse to disturbing those resting upon them. Again, adults would often rest upon each other, in what appeared to be a most uncomfortable manner for the one beneath, often pressing the head of the latter into the sand and completely blinding it for the time; yet I never saw the slightest evidence of ill-humor, not even when they were being fed. Often it happened that some sleepy fellow would quietly snap up the fly toward which another lizard was cautiously crawling, yet no fight ensued. Anything more trying than this to humanity can not be imagined, yet the lizards took every such occurrence as a matter of course.
In running, as well as when walking about deliberately, which they less often do, the lizard brings all four limbs equally into play, and their gait is much like that of a cat. When progress is suddenly arrested, they usually squat upon their hind-limbs only, holding their head well up and elevating the body, as does a cat or dog, by keeping the fore-limbs straight. Every attitude is suggestive of intelligence, and I refer particularly to the matter, because the differences in these respects between this lizard and the blue-tailed skink, the only other saurian found in New Jersey, is very marked; the latter, as we shall see, although having less suggestive manners, has, I believe, a greater degree of intelligence.
I have spoken of the rapid and complete submission of the pine-tree lizard when captured. While rowing from point to point along the rocky shores of Lake Hopatcong, Morris County, N. J., early in May, 1887, I chanced to see a beautiful "blue-tailed" skink, an old male that was now of a uniform rich brown color, and with a brilliantly red head. My one thought was to capture it—but how? I was in a profoundly cranky boat, and the water at this point was very deep. I tried a cold douche, and the bewildered skink, leaping into the lake, was caught as it clumsily swam toward shore. I placed it in a Wardian case. May 20th, and immediately it burrowed in the thick mat of sphagnum at the bottom, and for a week seldom if ever made its appearance. I could only determine that it was alive by searching for it, and invariably was bitten. It then showed a disposition to come from its inter-sphagnian retreat, but remained wholly suspicious of every sound or object that approached. Concealing myself, I watched it carefully, and found that the shutting of a door, the crowing of a cock near the window, and loud conversation in an adjoining room, always frightened it; while the singing of a canary, and of robins in a tree near by, were not noticed. A quickly passing shadow was particularly feared. Did it associate this with the birds of prey that are the skink's most dangerous enemies? Having disappeared, it never returned by the same burrow, but, cautiously peeping from a hole in an opposite corner of the case, studied the outlook for a long time before reappearing. It showed no disposition to be sociable until June 10th, when it seemed suddenly to gain confidence, but only to a slight degree. June 19th it ate for the first time, and then became somewhat tamer, but still was essentially wild, and seemed perhaps the more so because of the contrast with the pair of lizards that were all the while its companions. July 29th it was transferred to a roomy fernery belonging to a friend, where it found a close resemblance to its lake-side home in all essential features, and immediately it became more active; and now, nearly four months after capture, has become comparatively tame.
The skink, as we have seen, is exceedingly shy, irritable, and resents the slightest interference by biting savagely, but of course is entirely harmless. Nearly every prominent feature of the lizard is represented by an opposite trait in the skink. What appeared to be evidence of more sluggish wits than the lizard possesses, is the fact that it did not learn to associate my presence with a supply of food, as was true of the others, but the truth is it was its greater fear of man that held it back, and not really a want of cunning.
In many respects the skink recalls the snakes, and its manner of crawling, often without making any use of the posterior limbs, and generally keeping the body greatly bent, adds to the resemblance; and so, despite its shyness and courage when captured, evidences of intellectual strength, the skink seems lower in the scale of intelligence than the pine-tree lizard, but they are probably their superiors; and both are telling examples of the law of evolution.