IV
The last two weeks in October see the peak of the autumnal visitations. In November and December the stream from the inland shrinks, but the coast-wise stream, continuing to flow, brings us down a rare and curious world. Of this I shall write at greater length, for I found it of enormous interest.
Here, approaching the end of my notes on birds and autumn, I chance to remember that one of the strangest and most beautiful of the migrations over the dunes was not a movement of birds at all but of butterflies. There came a morning early in October which ripened, as the sun rose higher, into a rather mild and September-like day; the wind was autumnal, I recall, and from the north by west, but the current was both mildly warm and light. As it was a day to be spent out-of-doors, soon after ten o’clock I went out round the back of the Fo’castle into the sunlight and began to work there on a bin I was putting together out of driftage. I looked about, as I always do, but nothing in the landscape chanced to take my eye. Sawing and hammering, I worked for about three quarters of an hour, and then downed tools to take a moment’s rest.
During the hour, a flight of twenty or more large orange-and-black butterflies had arrived in the region of the dunes. It was a flight, yet were the individuals far apart. There was at least an eighth of a mile between any two; some were on the dunes, some were on the salt meadows, three were on the beach. Their movements were casual as the wind, yet there was an unmistakable southerly pull drawing them on. I tried to catch one of the travellers on the beach, and though I count myself a fair runner, it was no easy work keeping up with his turns and erratic doublings. I wished him no ill; I simply wanted to have a better look at him, but he escaped me by rising and disappearing over the top of a dune. When I reached the same top after a scramble up a steep of sand, the fugitive was already a good eighth of a mile away. I went back to my carpentry with an increased respect for butterflies as fliers.
An entomologist with whom I have been in correspondence tells me that my visitors were undoubtedly specimens of the monarch or milkweed butterfly, Anosia plexippus. In early autumn adults gather in great swarms and move in a generally southward direction, and it is believed (but not proved) that New England specimens go as far as Florida. The following spring individuals (not swarms) appear in the North apparently coming from the South. We do not know—I am quoting this paragraph almost verbatim—whether these are returning migrants or whether they are individuals that had not previously been in the North. We do know that none of the fall migrants had previously been in the South.
The butterflies of Eastham remained upon the dunes the rest of the morning. I imagine that they were in search of food. Between half-past twelve and half-past one they melted away as mysteriously as they had come, and with them went the last echo of summer and the high sun from the dunes. And that day I finished my bin and filled it and began to build a wall of seaweed round the foundation of my house. A cricket sang as I worked in the mild afternoon, alive and hardy in his cave under my driftwood mountain, and beyond this little familiar sound of earth I heard the roar of ocean filling the hollow space of day with its inexorable warning.