954 THE ENTOMOLOGIST S RECORD. 
Forres in Morayshire, and it occurred as late as November 4th at Wey- 
bridge, a few hybernators reappearing in the following spring, although 
they evidently failed to perpetuate their race here. In the same year 
(1872) the species occurred in extraordinary numbers in Holland (Hint. 
Mo, Mag., x., p. 20) where the insect is usually scarce, and there is no 
doubt that the simultaneous abundance in Holland and Britain was due 
to the same cause. Stainton considered that the species migrated from 
the Continent vid Scandinavia, other entomologists suggested that they 
came vid Holland, but no direct evidence was forthcoming as to the 
course taken by the migrants. We know the species was common in 
Holland, was it also common in Scandinavia ? One would suspect that 
the Dutch and British immigrants belonged to the same flight, whether 
that flight came from the north, or south, or east. The species was 
rather common again in 1880, a few in 1889 and 1900, but in other 
years only single examples have been recorded. 
Apart from the butterflies which are regularly exterminated here by 
conditions, of which, at present, we have no real knowledge, there are 
others, which, regular inhabitants of our islands, have at irregular 
periods, their numbers greatly increased by immigration. Such are 
the two common species, Pieris rapae and P. brassicae, of which many 
flocks haye been observed when on their migration journeys. We 
have ourselves seen Pieris brassicae (1887) come inland over the 
Straits of Dover in vast swarms, extending along the coast from Deal 
to the South Foreland. Other observers have witnessed similar 
occurrences on the Sussex, Lincoln and Norfolk coasts. The arrival 
of one of these migrating bodies is very characteristic of most. One 
sees at first a few butterflies coming towards, although at some distance 
from, the land, rising and falling, and occasionally even resting, upon 
the water. Soon the advance guard reaches the shore, whilst others 
rapidly come in. There seems never to be a crowd, or a very great 
number gathered together in a small space, but, ike huge white snow- 
flakes, they follow on continuously and without a break, and they are 
spread over a very considerable area. Many are in almost perfect 
condition, others considerably worn and often ragged. As soon as 
they arrive they appear to gather on almost every flower within a few 
hundred yards of the shore. ‘The immigration we witnessed, however, 
soon dispersed inland, and, in the course of a few hours or so, very 
few remained in the immediate neighbourhood of the original landing- 
place. There are many interesting records of the observations made on 
Pieris rapae and P. brassicae w hen they have been actually crossing 
the sea. On July 5th, 1846, a large flight crossed the English 
Channel to Dover, and it is stated (Zoologist, iv., p. 1448) that such 
was the density and extent of the cloud formed by the lying mass, 
that it completely obscured the sun from the people on board the 
continental steamers, and the decks were strewn in all directions with 
the insects. The flight reached England at noon, and dispersed itself 
inland and along the shore. During the sea-passage of the butterflies, 
the weather was calm and sunny with scarcely a puff of wind stirring, 
but in an hour or so after they reached tera firma it came on to blow 
ereat guns from the direction whence the insects came.’’ Another 
account of the same flight adds that ‘‘ every vessel that came into the 
harbour had the rigging and deck completely covered with them, and 
the pier was so thickly strewn with butterflies that you could not walk 
