In January the Pine Caterpillar sheds his skin for the second time. He is not nearly so pretty afterwards, but he has gained some new organs which are very useful. The hairs on the middle of his back are now of a dull reddish color, made paler still by many long white hairs mixed in with them. This faded costume has an odd feature. On the back may be seen eight gashes, like mouths, which open and close at the Caterpillar’s will. When the mouths are open there appears in each of them a little swelling, which seems extremely sensitive, for at the slightest irritation it goes in again.
What is the use of these queer mouths and tumors, as we call the little swellings? Certainly not to breathe with, for no one, not even a Caterpillar, breathes from the middle of his back. Let us consider the habits of the Pine Caterpillar, and perhaps we shall find out.
The Pine Caterpillar is most active during the winter, and at night. But if the north wind blow too violently, if the cold be too piercing, if it snow, or rain, or if the mist thicken into an icy drizzle, the Caterpillars prudently stay at home, sheltering under their waterproof tent.
It would be convenient to foresee these disagreeable weather conditions. The Caterpillar dreads them. A drop of rain sets him in a flutter; a snowflake exasperates him. To start for the grazing-grounds at dark of night, in uncertain weather, would be dangerous, for the procession goes some distance and travels slowly. The flock would have a bad time of it before regaining shelter, if they were caught in a sudden storm, such as are frequent in the bad season of the year. Can the Pine Caterpillar possibly be able to foretell the weather? Let me tell how I came to suspect this.
One night some friends came to see my Caterpillars in the greenhouse start on their nightly pilgrimage. We waited till nine o’clock, then went in. But, but ... what is this? Not a Caterpillar outside the nests! Last night and on the nights before they came out in countless numbers; to-night not one is to be seen. We waited till ten o’clock, till eleven, till midnight. Then, very much mortified, I had to send my friends away.
Next day I found that it had rained in the night and again in the morning, and that there was snow on the mountains. Had the Caterpillars, more sensitive than any of us to atmospheric changes, refused to venture out because they had known what was going to happen? After all, why not? I thought I would keep on observing them.
I found that whenever the weather chart in the newspaper announced a coming depression of the atmosphere, such as is made by storms, my greenhouse Caterpillars stayed at home, though neither rain, snow, nor cold could affect them in their indoor shelter. Sometimes they foretold the storm two days ahead. Their gift for scenting bad weather very soon won the confidence of the household. When we had to go into town to buy provisions, we used to consult our Caterpillars the night before; and according to what they did, we went or stayed at home.
The second dress of the Pine Caterpillar, therefore, seems to bring with it the power to foretell the weather. And this power is probably given by the wide mouths, which yawn open to sample the air from time to time and to give a warning of the sudden storm.