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.
_Chapter III_