17 



Both the Cabbage Whites, Brassica and Rapa have strong migratory pro- 

 pensities, and are most abundant in some years, and very scarce in others, 

 In 1868 particularly, they were very scarce all over Britian, although it was 

 a fine hot summer. 



In 1818, these species abounded so greatly near the Metropolis, as to 

 attract the notice of the public journalists, and Mr. Stephens had a brood of 

 Brassica, which were scarcely seven complete days in the chrysalis state, the 

 thermometer during the period varying from 70 to 80. 



In 1842, a vast flight of white butterflies came over from the Continent 

 to the Kentish coast ; and Mr. Thorncroft published in the " Entomologist," 

 the following interesting observations on the subject. " It was a still hot 

 day, with hardly a breath of air, and now and then the common Brassica and 

 Rapte would lazily fly in. The flood tide set in about 3 p.m. with a gentle 

 breeze, and then came a host of the above named butterflies with a few of 

 Napi. What surprised my friends and myself was their alighting or settling 

 on the sea with expanded wings, and the ease with which they rose again. 

 The shore was covered with a coarse sort of rye-grass, on which they were 

 resting when we returned home, and in walking through the tall grass, they 

 rose in myriads." " On Sunday, the 5th of July, 1 846, one of the largest 

 flights of butterflies ever seen in this country crossed the Channel from 

 France to England. 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 of the Continental steamboats, and the decks were strewed with the 

 insects in all directions. The flight reached Dover about 12 o'clock, and 

 dispersed themselves along the shore and inland, darkening the air as they 

 went. During the sea passage of the butterflies, the weather was calm and 

 sunny with scarcely a puff of wind stirring ; but an hour or so it came on to 

 blow great guns from the South- West, the direction from which they came." 

 Extracted from the " Canterbury Journal." 



Rapce is a very thirsty butterfly, and fond of alighting on the wet mud at 

 the edges of ponds. In London, it may be observed following the water- 

 carts, and pitching on the recently sprinkled roads. More than once, in 

 going by the steamer from Weymouth to Lulworth, in hot and calm summer 

 weather, I have noticed a swarm of Pieris rapce, two hundred or more in 

 numbers, leave the land and fly out to sea. Sometimes the swarm would 

 remain apparently stationary for a while, and the individuals would disport 

 themselves somewhat after the manner of mayflies, evidently enjoying the 

 vapour arising from the briny ocean. 



