254 THE entomologist's recobd. 



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 (Ent. 

 Mo. Mag., x., p. 20) Avhere 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 via Scandinavia, other entomologists suggested that they 

 came rid Holland, but no direct evidence Avas 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. bmssicae, of which many 

 flocks have 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, like huge white snow- 

 flakes, they follow on continuously and Avithout 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 Avithin 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 

 feAV remained in the immediate neighbourhood of the original landing- 

 place. There are many interesting records of the observations made on 

 Pieris rapae and P. hrasucae when they have been actually crossing 

 the sea. On July 5th, 1846, a large flight crossed the English 

 Channel to Dover, and it is stated (Zooln<jist, iv., p. 1448) that such 

 was the density and extent of the cloud formed by the living mass, 

 that it completely obscured the sun from the people on board the 

 continental steamers, and the decks were streAvn 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 terra firma it came on to blow 

 great guns from the direction Avhence 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 Avith them, and 

 the pier Avas so thickly streAA'n Avitli butterflies that you could not Avalk 



