IN THE FACE OF THE COLD
When the full moon hangs high overhead, the snow creaks underfoot, the north wind roars with furious blast, and the trees of the forests crack in the frost with a report like that of cannon, then, hanging in its little nest on the bare branches of the wind-tossed trees, the tiny caterpillar of the Viceroy keeps the spark of life where men freeze and die. Nothing in the realm of nature is more wonderful than the manner in which some of the most minute animal forms resist cold. The genera Erebia and Œneis, and many species of the genus Brenthis, are, as we have already learned, inhabitants of the arctic regions or of lofty Alpine summits, the climate of which is arctic. Their caterpillars often hibernate in a temperature of from forty to fifty, and even seventy, degrees below zero, Fahrenheit.
It has been alleged that caterpillars freeze in the winter and thaw out in the spring, at that time regaining their vitality. Thus far the writer is unable to ascertain that any experiments or observations have positively decided for or against this view. A number of recorded cases in which caterpillars are positively stated to have been frozen and to have afterward been found to be full of vitality when thawed are open to question.
The most circumstantial account is that by Commander James Ross, R.N., F.R.S., quoted by Curtis in the Entomological Appendix to the "Narrative" of Sir John Ross's second voyage to the arctic regions. The specimens upon which the observations were made were the caterpillars of Laria rossi, a moth which is found abundantly in the arctic regions of North America. I quote from the account: "About thirty of the caterpillars were put into a box in the middle of September, and after being exposed to the severe winter temperature of the next three months, they were brought into a warm cabin, where, in less than two hours, every one of them returned to life, and continued for a whole day walking about; they were again exposed to the air at a temperature of about forty degrees below zero, and became immediately hard-frozen; in this state they remained a week, and on being brought again into the cabin, only twenty-three came to life; these were, at the end of four hours, put out once more into the air and again hard-frozen; after another week they were again brought in, when only eleven were restored to life; a fourth time they were exposed to the winter temperature, and only two returned to life on being again brought into the cabin; these two survived the winter, and in May an imperfect Laria was produced from one, and six flies from the other."
The foregoing account seems to verify more thoroughly the stories that have been told than anything else I have been able to discover within the limits of entomological literature, but does not conclude argument. It would be interesting in these days, when methods of artificial freezing have been so highly perfected, to undertake a series of experiments to prove or disprove, as the case may be, the view which has been held since the time of the ancients. There is here a field for nice investigation on the part of some reader of this book. In making the experiment it probably would be well to select the larvæ of species which are known to hibernate during the winter and to be capable of withstanding a great degree of cold.
The effect of cold suddenly applied to the chrysalids of butterflies at the moment of pupation is often to produce remarkable changes in the markings. The spots upon the wings of butterflies emerging from chrysalids thus treated are frequently rendered more or less indistinct and blurred. The dark markings are intensified in color and enlarged; the pale markings are also in some cases ascertained to experience enlargement. Many of the strange and really beautiful aberrations known to collectors have no doubt been produced by the action of frost which has occurred at the season when the larva was pupating. The species believed by the writer to be most prolific in aberrations are species which pupate early in the spring from caterpillars which have hibernated or which pupate late in the autumn. Some are species found at considerable altitudes above sea-level, where late frosts and early frosts are apt to occur. A number of very beautiful experiments upon the effect of cold upon the color of butterflies have been made in recent years, and some very curious phenomena have been observed. The writer has in his collection a considerable number of strikingly aberrant specimens which emerged from chrysalids treated to a sudden artificial lowering of the temperature at the critical period of pupation.
SUBFAMILY LIBYTHEINÆ (THE SNOUT-BUTTERFLIES)
"What more felicitie can fall to creature Than to enjoy delight with libertie, And to be Lord of all the workes of Nature, To raigne in th' aire from th' earth to highest skie, To feed on flowres and weeds of glorious feature, To take whatever thing doth please the eie?"