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MIGRATION OF PIERIS BRASSICAE OBSERVED
AT HARWICH.
By F. KERRY.
THERE has been, this summer, an immense immigration of
Pieris brassicae from the Continent to this portion of the
east coast. On Thursday, the 11th of August, and for several
days after, large numbers of this butterfly were to be seen coming
over the sea, and many were drowned in the water. The lobster
catchers, who fish about five or six miles from the shore, told me you
could not look anywhere over the sea without seeing white butterflies
making for the shore, all coming from the S.E. and flying N.W. At
Harwich thousands of the Pieris could be observed in the gardens
busily depositing their eggs, with dire consequences to the vegetables.
The resulting larva must have been present in millions. Nearly all the
broccoli, cabbage, savoys, and brussel sprouts were eaten up, nothing
remaining of the plants but the main ribs.
No one in this neighbourhood remembers a similar visitation
before. Ichneumons (probably Apanteles glomeratus, L.) have
destroyed the greater part of the larvae in some gardens. At the
"Phoenix Hotel," Dovercourt, quite four-fifths of the caterpillars
were so destroyed; while at the Trinity Houses, about two hundred
yards off, the pupae are in considerable excess of the yellow patches
of Ichneumon cocoons; I took 250 pupae there in about ten
minutes, thus demonstrating the prodigious numbers of the insects.
[We have pleasure in giving prominence to Mr. Kerry's note,
inasmuch as such observations have an important bearing upon all
theories of the distribution and erratic appearance of various species of
insects in Britain. There can be little doubt that many of our
insects, such as the Colias, Parameus cardui, Plusia gamma, and others
which appear occasionally in great numbers, and may then disappear
or become very rare for years together, are migratory; and that the
specimens which occasionally delight our eyes in numbers are
either immigrants or the immediate offspring of immigrants from the
Continent. More than twenty years ago the immense swarms of
''Lady-bird" beetles (Cocinella) which made their appearance on
parts of the English coast attracted much popular attention, and led
to alarming outbursts of "newspaper science." Several direct
observations of immigration of insects into England are on record.
A very remarkable instance was given in The Essex Naturalist for
1888 (vol. ii., p. 158), the insect being a Dragon-fly (Libellula
quadrimaculata) observed off the Essex coast near Shoebury-
ness.—Ed.]