70 



flakes, and to have continued for fully an hour against a fairly 

 fresh breeze, the insects constantly passing inland on their 

 arrival {Entom. vii. i6i). A similar flight had previously 

 been noted. 



Swarms of Pieris brassicce have been encountered in the 

 North Sea, during an excursion on board a fishing boat from 

 Bremer-haven. So long as the boat was in the river, or at 

 its mouth, only an occasional specimen 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 {E.M.M. ix. 246), 



An account is also given of a swarm of white butterflies 

 being overtaken in the English Channel by a vessel on its 

 homeward journey from Havre, and is thus described : " We 

 seemed to suddenly 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" {E.M.M. vii. 18). 



Then again, we have an instance of observed immigration 

 on the Sussex coast, and witnessed from Shoreham pier. 

 The day is described as hot and still, with an occasional P. 

 brassicce flying in, when, on the setting in of the afternoon 

 flood-tide, there came a host of them direct from the sea 

 from a south-westerly direction, and settled on the coarse 

 grass along the shore, whence they afterwards rose in 

 myriads upon being disturbed. It was noticed that some of 

 these butterflies, before arrival, settled for a time on the sea, 

 and rose again after resting, a habit which appears to be not 

 infrequent with this species {Entom. ii. 289). 



Let us, however, leave this species, and glance at another 

 that stands in a somewhat difierent category : — 



Colias edusa^ Fb., although by no means generally common 

 in Britain, has occurred at intervals in considerable abundance 

 throughout the country. This has given rise to an enormous 

 mass of recorded evidence with regard to it, and an equally 

 large amount of speculation as to the causes of its irregular 

 appearance. It was, at one time, suggested that some 

 mysterious agency produced it in abundance every seven 

 years ; but an examination of the dates of the appearances 

 during the present century showed that to be a mere ima- 

 gination in the minds of its propounders, and the possibility 

 of the ova being introduced into this country with French 

 clover seed may be regarded as equally unreliable. It will 

 be seen, on looking at the dates when it has been common, 

 that they are very irregular. It was abundant in 1804, 8, 11, 



