MIGRATION AND DISPERSAL OF INSECTS. LEPIDOPTERA. 255 
without treading on them.” Crompton records (Ant. Mo. May., vil., 
p. 18) that at the end of August, 1849, he was crossing from Havre by 
steamboat, and that ‘‘about ‘midday the vessel seemed to plunge into a 
swarm or snow-shower of common White butterflies, and so continued 
for nearly an hour. They literally covered us, circling round and 
playing up and down the vessel, and | was struck with the fact that 
they seemed to keep up with the vessel’s speed—about eight knots an 
hour—as well as to flutter up and down. Either they flew at our 
pace easily, or were assisted by the air carried along with us in the 
calm. Gradually they thinned off, and a breeze arising, disappeared. 
At the same time an exhausted pigeon fell on board, and, a thunder- 
storm on the English coast coming in sight, our pleasant Sunday 
trip closed with a beauty of a different kind. I noticed in the papers 
a few days afterwards a paragraph about a large flight of white butter- 
flies having crossed the Channel and landed on the Hampshire coast, 
and thought I had seen them on their passage.’ Another observer 
who was on an excursion in a fishing-boat in the North Sea, near the 
mouth of the Weser, in July, 1872, writes: “So long as the boat was in 
the river, or at its mouth only an occasional Cabbage White was to be 
seen crossing the river, and soon disappearing, but, when once out at 
sea the boat was enveloped in a swarm of these butterflies, so thick as 
to resemble a snowstorm. ‘The weather was hot, and the surface of 
the sea undisturbed by any wind. Many of the insects were to be 
seen poising themselves with erect wings on the surface, others were 
lying flat on it, as if dead, but flew away rapidly if disturbed. They 
were accompanied by dragonflies (dischna) which evidently preyed 
upon them, and also by small flies and ichneumons.”’* It is further 
recorded by Dis Sonala that, in a dead calm off Nordeney, in the 
Baltic Sea, he steamed for three hours and for a distance of thirty 
miles, through a continuous flock of Pieris rapae; he was at the time 
some thirty miles from the mainland, and only five miles less than 
that from the nearest island. ‘The shore was afterwards found to be 
strewn with their dead bodies. In July, 1864, on a still, hot day, 
- with hardly a breath of air, Thorncroft records (Hntom., il., pp. 289- 
290) a large immigration of P. brassicae and P. rapac, at Shoreham. 
He was ‘‘ on the pier about 8 p.m., when the flood-tide set in with a 
gentle breeze, and then came a host of the above named butterflies, 
with a few of P. napi. There must have been hundreds arrive within 
a very short space of time.’’ He expresses his surprise at ‘“ their 
alichting and settling on the sea, with expanded wings, and the ease 
with which they rose again, the same butterfly settling and rising 
as many as four or five times within a distance of a hundred yards, 
and with apparently as much ease as on land ; they all came direct in 
from the sea from a south-westerly direction, and seemed to aim for 
the entrance of the harbour between the piers, though there were 
plenty of them came on shore on each side of the piers. The shore 
was covered with a coarse sort of Italian rye-grass, on which they were 
resting when we returned home, and, in walking through the tall 
grass, they rose in myriads.” Robson gives (Youny Naturalist, 1., p. 
29) an interesting account of an immigration of Pieris brassicae that 
* One wonders much what ichneumons were doing amongst a swarm of the 
imagines of the Picris. 
